Hematology — ASCP Exam Prep Thrombotic Disorders Part 1

Master inherited thrombophilias — Factor V Leiden, Protein C/S deficiency — and their lab workup for ASCP BOC.

ASCPprep.com | Hematology & Hemostasis

Chapter 25 — THROMBOTIC DISORDERS AND LABORATORY ASSESSMENT

ASCP Board Exam · Lab-Focused Study Guide

Thrombophilia · Venous vs Arterial Thrombosis · Acquired & Congenital Risk Factors · Antiphospholipid Antibodies & Lupus Anticoagulant Algorithm · APC Resistance / Factor V Leiden · Prothrombin G20210A · Antithrombin · Protein C & S · Arterial Predictors (HSCRP, Homocysteine, Fibrinogen, Lp(a)) · DIC · TAT & F1+2 · Heparin-Induced Thrombocytopenia (4Ts) · Practice Questions

1 · Priority Table & Quick Foundation

Topic	Priority	Why It’s Tested
Factor V Leiden (R506Q) — APC resistance ratio <1.8, molecular confirmation	HIGH	Most common inherited thrombophilia (Rodak Q5, Q11)
Lupus anticoagulant: mixing, screen (DRVVT, LA-sensitive PTT), confirm with high phospholipid	HIGH	ISTH steps (Rodak Q6, Q10)
Antiphospholipid antibodies: ACL, anti-β₂-GPI; repeat after 12 weeks	HIGH	Persistence defines significance
AT, protein C, protein S assays; timing (14 days off anticoagulant), acquired causes	HIGH	Case study; interpretation pitfalls
Protein S deficiency types I, II, III (Table 39-6)	HIGH	Rodak Q7
DIC: causes, pathophysiology, profile (platelets, PT, PTT, D-dimer, fibrinogen)	HIGH	Table 39-14, 39-15
HIT: IgG anti-heparin–PF4, 4Ts, timing, lab tests (SRA), treatment (argatroban)	HIGH	Emergency recognition
Prothrombin G20210A — molecular only	MEDIUM	No phenotypic assay
Coumadin-induced skin necrosis and protein C	MEDIUM	Classic complication
Arterial predictors: HSCRP, homocysteine, fibrinogen, Lp(a), lipids	MEDIUM	Rodak Q8, Q9
Acquired risk factors (Tables 39-1, 39-2) and double hit	MEDIUM	Rodak Q3, Q4
TAT and prothrombin fragment 1+2	LOW	Localized thrombosis markers

🎯 KEY POINT — Where to spend your time

Focus: FVL/APC resistance test, LA algorithm (DRVVT screen → high-PL confirm, ratio 1.2), APL persistence at 12 weeks, when AT/PC/PS can be tested, protein S types, DIC profile, HIT 4Ts and treatment. Skim: relative risk tables for HSCRP/cholesterol, Lp(a) race ranges, prevalence statistics.

Quick Foundation — from zero

Thrombosis = inappropriate clot (platelet or fibrin) blocking a vessel → ischemia and necrosis.
Venous clots (DVT → pulmonary embolism) are fibrin-rich “red clots” driven by stasis and coagulation imbalance. Arterial clots (heart attack, stroke) are platelet-rich “white clots” on ruptured atherosclerotic plaque.
Thrombophilia (hypercoagulability) = predisposition to thrombosis from a congenital or acquired disorder: too much activation, too little control, or suppressed fibrinolysis.
Most people clot because of a “double hit” — e.g., factor V Leiden plus oral contraceptives, pregnancy or immobilization.
The lab looks for inherited defects (FVL, prothrombin G20210A, AT/PC/PS deficiency), acquired antibodies (lupus anticoagulant) and consumption states (DIC, HIT).

💡 Analogy

Clotting is a car with an accelerator and brakes. Thrombophilia happens when the accelerator sticks (prothrombin G20210A — too much fuel), the brakes fail (AT, protein C or S deficiency), or the brakes can’t grip (factor V Leiden — APC can’t cut factor Va). Lupus anticoagulant is a faulty dashboard gauge: in the test tube it reads ‘slow’ (prolonged PTT), yet on the road the car speeds (thrombosis). DIC is running out of both gas and brake fluid at once — clotting everywhere, then bleeding everywhere.

🏥 Why this matters clinically

Thrombosis causes one in three U.S. deaths. Finding FVL in a young woman changes contraceptive choices (30× risk with OCPs). Testing protein C/S/AT during acute thrombosis or on warfarin gives false ‘deficiencies’ — the lab must time tests correctly. Missing HIT and continuing heparin can cause limb gangrene, stroke or death (20% mortality).

Concept	Plain-English Explanation
Thrombophilia	Predisposition to thrombosis from a congenital or acquired disorder
VTE	Venous thromboembolism — DVT and pulmonary embolism
APC resistance	Factor Va resists cleavage by activated protein C
Lupus anticoagulant	Antiphospholipid antibody prolonging clot tests in vitro but causing thrombosis in vivo
Mixing study	Patient + normal plasma 1:1 — doesn’t correct → inhibitor
DIC	Systemic activation of coagulation consuming platelets and factors
HIT	Antibody to heparin–PF4 complexes activating platelets → thrombosis
Double hit	Combination of risk factors (genetic + acquired) that triggers clotting

2 · Core Content Tables

2.1 History of Thrombosis Risk Testing

Feature	Details
Before 1992	Only AT, protein C, protein S deficiencies — together ≤7% of recurrent VTE; no link to arterial disease
1993	Dahlbäck: APC resistance
1994	Bertina: factor V Leiden mutation as its cause
Current panel	AT, protein C, protein S, APC resistance, FVL, prothrombin G20210A, LA; D-dimer, F1+2, TAT

2.2 Etiology & Prevalence

Feature	Details
Thrombosis	Inappropriate platelet/fibrin clots from abnormal flow (stasis), coagulation, platelets, leukocyte activation or vessel wall
Thrombophilia causes	Inflammation releasing prothrombotic mediators; uncontrolled platelet activation; uncontrolled coagulation; suppressed fibrinolysis
Burden (2010)	1 in 3 U.S. deaths; 25% of initial events fatal; many undiagnosed until autopsy
VTE incidence	1 in 1000/year; more in African Americans and women of childbearing age
DVT	Iliac, popliteal, femoral, calf veins; pain, heat, redness, swelling (whole leg)
Pulmonary embolism	~95% from deep leg/calf veins; 250,000/year in U.S.; 10–15% die within 3 months; often misdiagnosed
Arterial	Cardiovascular disease 380,000 premature deaths; strokes 790,000; ~80% MIs and 85% strokes from thrombi; mechanism: unstable atherosclerotic plaque rupture → platelets + VWF → white thrombi

2.3 Nondisease Risk Factors (Rodak Table 39-1)

Risk Factor	Contribution	Lab
Age	Risk doubles each decade after 50
Immobilization	Driving, air travel, bed/wheelchair, obesity — slowed flow
Diet	Low folate, B₆, B₁₂ → homocysteinemia 2–7× arterial/venous risk	Homocysteine, vitamins, lipids
Lipid imbalance	Arterial risk with ↑ LDL-C, Lp(a), ↓ HDL-C	Lipid profile, Lp(a)
Oral contraceptives	4–6×
Pregnancy	3–5×
Hormone replacement	2–4×
Femoral/tibial fracture	80% thrombosis if untreated
Hip, knee, gynecologic, prostate surgery	50% if untreated
Smoking, chronic inflammation	Arterial	HSCRP
Central venous catheter	33% of children develop VT

2.4 Diseases with Thrombotic Risk (Rodak Table 39-2)

Disease	Effect	Lab
Antiphospholipid syndrome	1.6–3.2× stroke, MI, recurrent abortion, VTE	PTT mixing, LA profile, ACL, anti-β₂-GPI
Myeloproliferative neoplasms (ET, PV, CML)	Viscosity, platelet activation	Platelet count, aggregometry
Hepatic disease	↓ control proteins, excess thrombin	PT, PC, PS, AT, factors
Adenocarcinoma — Trousseau syndrome	20× risk; low-grade chronic DIC; 10–20% of idiopathic VTE have cancer	DIC profile
Leukemia (APL M3, M4–M5)	Chronic DIC	DIC profile
PNH	DVT, PE, DIC (≥40% thrombose)	Flow CD55/CD59, DIC profile
Chronic inflammation (diabetes, cancer, obesity, smoking)	↑ fibrinogen, VIII; ↓ free PS	Fibrinogen, HSCRP
Others	Diabetes (6× CVD), heart failure, atrial fibrillation, nephrotic syndrome (AT loss)

2.5 Congenital Risk Factors (Rodak Tables 39-3, 39-4)

Factor	Mechanism	Risk	Prevalence (general / recurrent VTE)	Tests
AT deficiency	AT inhibits IIa, IXa, Xa, XIa (heparin enhanced)	Het 10–20×; homozygous 100% (rare)	1/2000–1/5000 / 1–1.8%	Clot/chromogenic activity, antigen
PC deficiency	APC digests Va, VIIIa (needs PS)	Het 2–5×; homozygous 100%, neonatal purpura fulminans	1/300 / 2.5–5%	Clot/chromogenic activity, antigen
Free PS deficiency	APC cofactor; 40% free, 60% on C4bBP	Het 1.6–11.5×; homozygous purpura fulminans	Unknown / 2.8–5%	Clot activity, free/total antigen
APC resistance (FVL)	R506Q gain of function — Va resists APC	Het 3×; homozygous 18×	3–8% Caucasians (rare Asians/Africans) / 20–25%	PTT-based APC resistance + molecular
Prothrombin G20210A	3′ UTR mutation → ↑ prothrombin (~130%)	Het 1.6–11.5× (2–3×)	2–3% Caucasians / 4–8%	Molecular only
Hyperfibrinogenemia	Arterial thrombosis	Under investigation	—	Clauss, immunoassay
Hyperhomocysteinemia (MTHFR)	—	—	11% / 13–27%	Homocysteine

2.6 When to Suspect Congenital Thrombophilia

Feature	Details
Clues	Thrombosis in young adults; unusual sites (mesenteric, renal, axillary veins); recurrent; family history
Most common inherited	FVL; second: prothrombin G20210A
Rarity	PC, PS, AT deficiencies together only 0.2–1% of world population
Double hit	FVL het + OCP → 30-fold risk; homocysteinemia 3×, FVL 2×, both 10× (Physicians’ Health Study)
Acquired APC resistance	Pregnancy, oral contraceptives (without FVL)

2.7 Thrombophilia Laboratory Profile (Rodak Table 39-5)

Assay	Reference	Comments
APC resistance	Ratio ≥1.8	Clot-based screen using PTT with factor V–depleted plasma
Factor V Leiden	Wild type	Molecular follow-up to ratio <1.8
Prothrombin G20210A	Wild type	Molecular; no phenotypic assay
LA profile*	Negative	≥2 clot-based assays (PTT and DRVVT; KCT or dilute PT secondary) with phospholipid neutralization
ACL antibody	IgG <12 GPL; IgM <10 MPL	Immunoassay; depends on β₂-GPI
Anti-β₂-GPI	<20 G units	Immunoassay
AT activity*	78–126%	If consistently low → AT antigen
PC activity*	70–140%	If low → PC antigen
PS activity*	65–140%	If low → total and free PS antigen, C4bBP
Fibrinogen	220–498 mg/dL	Elevation associated with arterial thrombosis

*Inaccurate during active thrombosis and anticoagulant therapy — perform 14 days after anticoagulation is discontinued. The presence of risk factors doesn’t change treatment of an ongoing thrombosis.

2.8 Antiphospholipid (APL) Antibodies

Feature	Details
Family	Immunoglobulins binding protein–phospholipid complexes: LA (clot-based), ACL and anti-β₂-GPI (immunoassay)
Isotypes	IgM, IgG, IgA; ‘nonspecific inhibitors’
Main target	β₂-glycoprotein I; also annexin V, prothrombin
APS	Chronic autoimmune APL → TIAs, strokes, coronary and peripheral artery disease, VTE, recurrent pregnancy loss
Prevalence	1–2% unselected; 5–15% of recurrent thrombosis patients
Transient (alloimmune)	After infection or drugs (Box 39-1); disappear within 12 weeks; no clinical consequence
Drugs inducing APL (Box 39-1)	Antibiotics, phenothiazine, hydralazine, quinine/quinidine, calcium channel blockers, procainamide, phenytoin, cocaine, elevated estrogens
Autoimmune	50% of SLE patients; also RA, scleroderma, Sjögren; primary APS without disease; ~30% associated with thrombosis; chronic APL without disease 1.8–3.2× risk
Suspect when	Unexplained venous/arterial thrombosis, thrombocytopenia, recurrent fetal loss, or unexplained prolonged PTT not correcting on mixing

2.9 Lupus Anticoagulant Testing — Principles

Feature	Details
Why two systems	LA is heterogeneous; positive in either is conclusive → use two parallel systems
Primary systems	DRVVT (dilute Russell viper venom time; activates factor X; most specific) + silica-based low-phospholipid PTT (activates XII)
Older systems	Kaolin clotting time (KCT; XII) and dilute thromboplastin time (DTT/TTI; VII)
ISTH 2009 steps	(1) Prolonged phospholipid-dependent screen (low-PL PTT or DRVVT) · (2) no correction on mixing with normal platelet-poor plasma · (3) shortening/correction with excess phospholipid · (4) exclude other coagulopathies
Specimen	Platelet-poor plasma (<10,000/µL) — platelet phospholipid (and fragments from freezing) neutralizes LA → false negative

2.10 Mixing Study Algorithm (Figure 39-1)

Feature	Details
PTT long	Thrombin time (TT) to detect unfractionated heparin
TT long	Hepzyme (heparinase) → repeat PTT; normal → heparin present
TT normal (or PTT still long)	Mix 1:1 with NP → PTT
Uncorrected immediately	Assay for lupus anticoagulant
Corrects	Incubate new 1:1 mix 37 °C, 1–2 h → repeat PTT
Incubated corrects	Factor deficiency → factor assay
Incubated uncorrected	Specific factor inhibitor (e.g., anti-VIII)
‘Correction’ definitions	Rosner index; within 10% of NP; within 5 s of NP; within reference interval (lab decides)

2.11 LA Algorithm — DRVVT and PTT (Figure 39-3)

Feature	Details
DRVVT screen ratio	Patient seconds ÷ NP seconds; >1.2 → LA presumed
DRVVT confirm	Mix patient with high-phospholipid DRVVT reagent; screen ÷ confirm >1.2 → LA confirmed
If DRVVT screen ≤1.2 (or confirm ≤1.2)	Silica low-PL PTT screen → >1.2 → PTT confirm with high-PL reagent → >1.2 = LA
Variations	Absolute difference (e.g., 8 s); each lab sets thresholds
Normalized ratio	(Patient screen/screen MRI) ÷ (patient confirm/confirm MRI)

2.12 APL Immunoassays

Feature	Details
ACL	Microplate coated with bovine cardiolipin + bovine β₂-GPI; enzyme-labeled anti-IgG/IgM/IgA; units GPL, MPL, APL (1 unit = 1 µg/mL standard). Coexists with LA in 60%. Not affected by heparin, oral anticoagulants, thrombosis or factor deficiency
Anti-β₂-GPI	IgG and IgM; >20 units correlates with thrombosis more closely than ACL
Antiphosphatidylserine	When APS suspected but others negative; ≥16 IgG or 22 IgM units positive; reference labs
Persistence rule	Any positive APL assay → repeat on a new specimen after ≥12 weeks; positive again = chronic, clinically significant

2.13 APC Resistance & Factor V Leiden

Feature	Details
Mutation	Factor V gene: glutamine replaces arginine at position 506 (R506Q) — Arg506 is an APC cleavage site → Va resists hydrolysis → more thrombin
Name	City of Leiden, Netherlands
Prevalence	3–8% of northern European Caucasians; also Arabs, Hispanics; nearly absent in Africans and East Asians
Risk	Heterozygous 3×; homozygous 18×
Clot-based assay	Patient plasma mixed 1:4 with factor V–depleted plasma + PTT reagent; aliquot 1 + CaCl₂; aliquot 2 + CaCl₂ + APC. Ratio (with APC ÷ without) normally ≥1.8; <1.8 = APC resistance
Why V-depleted plasma	Compensates for factor deficiencies and oral anticoagulant therapy
Interferences	Use platelet-poor plasma (PF4 release); reagents neutralize UFH (polybrene/heparinase); LA interferes → go straight to molecular test
Confirmation	Molecular FVL assay — determines zygosity

2.14 Prothrombin G20210A

Feature	Details
Mutation	Guanine → adenine at base 20210, 3′ untranslated region of prothrombin gene
Effect	Mildly elevated prothrombin (~130%)
Prevalence	0.3–2.4% worldwide; 5–18% of familial thrombosis
Risk	Heterozygotes 2–3×
Test	Molecular only — prothrombin activity overlaps with normal

2.15 Antithrombin

Feature	Details
Function	Serpin neutralizing IIa, IXa, Xa, XIa, XIIa (all serine proteases except VIIa); enhanced by UFH, LMWH, fondaparinux; first control protein assayed routinely
Acquired deficiency	Liver disease, nephrotic syndrome, prolonged heparin therapy, asparaginase, oral contraceptives, DIC
Congenital	1/2000–1/5000; 1–1.8% of recurrent VTE. Type I (~90%): quantitative · type II: nonfunctional (protease or heparin binding site)
Reference	Activity 78–126%; antigen 22–39 mg/dL (68–128%); half-life 72 h; adult levels by 3 months; ↓ with age and pregnancy
Chromogenic activity assay	Patient plasma + heparin + measured Xa; AT binds Xa; residual Xa cleaves chromogenic substrate → yellow pNA — color inversely proportional to AT. Detects quantitative + protease-site defects but misses heparin-binding site defects (clot-based detects both)
Antigen	Turbidimetric latex immunoassay; ↓ in type I only
Pitfalls	Coumadin may raise AT (masks mild deficiency); stays low 10–14 days after surgery/thrombosis
Heparin resistance	Heparin gives no anticoagulant effect and no PTT response → assay AT; treat with AT concentrate (Thrombate III)

2.16 Protein C & Protein S

Feature	Details
Pathway	Thrombin + thrombomodulin → protein C → APC; APC + free PS (40%) hydrolyze Va and VIIIa
Protein S forms	40% free (active), 60% bound to C4bBP (acute phase reactant — inflammation lowers free PS)
Risk	Heterozygous 1.6–11.5× recurrent DVT/PE; PS deficiency also TIAs/strokes in young
Reference	PC and PS activity and antigen 65–140%; heterozygotes 30–65%
Coumadin skin necrosis	PC half-life ~6 h (like VII) → in heterozygous PC deficiency PC drops below 65% before factors reach therapeutic <30% → dermal vessel thrombosis, painful necrosis after pruritus. Prevent: overlap LMWH or fondaparinux with Coumadin until stable INR
Timing	PC and PS stay low 10–14 days after Coumadin, surgery or thrombosis; low in pregnancy, liver/renal disease, vitamin K deficiency, DIC, OCPs
Homozygous	Neonatal purpura fulminans — rapidly fatal; factor concentrates + lifelong Coumadin
PC chromogenic assay	Protac (Agkistrodon contortrix, southern copperhead venom) activates PC → APC cleaves chromogenic substrate (S-2366) → pNA; misses phospholipid/PS binding-site defects
PC clot-based	PC-depleted plasma + PTT + Protac → APC prolongs PTT ∝ PC. Overestimated by heparin >1 IU/mL, APC resistance, LA, direct thrombin inhibitors (argatroban, dabigatran)
PC antigen	EIA; detects quantitative only — use after low activity
PS assay	No chromogenic assay; clot-based: PS-depleted plasma + APC + Russell viper venom → prolongation ∝ PS. Same interferences; VII cold activation (4–10 °C) underestimates PS. Follow with total and free PS antigen

2.17 Protein S Deficiency Types (Rodak Table 39-6)

Type	PS Activity	PS Free Antigen	PS Total Antigen	C4bBP
I — Quantitative	<65%	<65%	<65%	Normal
II — Qualitative	<65%	>65%	>65%	Normal
III — Inflammation	<65%	<65%	>65%	Elevated

2.18 Markers of Arterial Thrombosis Risk (Rodak Table 39-7)

Marker	Reference	Comments
HSCRP	0.3–1.7 mg/L	Inflammation marker; stable, reproducible; chronic ≥1.5 mg/L → atherosclerosis risk
Fibrinogen	220–498 mg/dL	Chronic >300 mg/dL ↑ risk; poor reproducibility across platforms
Homocysteine	4.6–12.1 µmol/L	Lowered by B₆, B₁₂, folate
Total cholesterol	<200 mg/dL	Reproducible
TC:HDL-C	<10	Reproducible
LDL-C	<130 mg/dL	Lowered by statins
Lipoprotein (a)	2.2–49.4 mg/dL	Varies with race and age; lowered by statins

2.19 Arterial Predictors — Details

Feature	Details
Lipids	1/3 of events occur with normal lipids; half of people with lipid risk never have an event
CRP	Calcium-dependent pentameric pentraxin from liver; <0.55 mg/L normally; rises 1000-fold 6–8 h after inflammation; HSCRP (late 1990s) detects slight chronic elevation; independent predictor (Table 39-8: women top quartile 5.5×); combined with cholesterol/TC:HDL raises predictive value; monitors statin anti-inflammatory effect
Homocysteine	Sulfur amino acid from methionine; regulated by cystathionine β-synthase (B₆), MTHFR, methionine synthase (B₁₂). Relative risk: coronary 1.7, cerebrovascular 2.5, peripheral 6.8. MTHFR C677T homozygosity is not an independent risk. Mechanism: endothelial damage. No trials show lowering prevents events
Homocysteine reference (Table 39-11)	Females ≤60 4.6–12.1; >60 6.6–14.1 · males ≤60 5.0–15.6; >60 7.0–17.6 µmol/L
Fibrinogen	Risk triples from lowest to highest quintile (Table 39-12: 1.0 → 2.89); synergy with cholesterol; binds GP IIb/IIIa; no specific therapy; methods not normalized
Lipoprotein (a)	LDL-like; competes with plasminogen for binding on fibrin → antifibrinolytic; higher in African Americans but stronger predictor in Caucasians; statins lower it
Fibrinolytic predictor	Elevated PAI-1 associated with arterial risk (Rodak Q8)*

*PAI-1 link to arterial risk is stated in Rodak Ch. 37 (↑ PAI-1 in metabolic syndrome, atherosclerosis, stroke).

2.20 Disseminated Intravascular Coagulation (DIC)

Feature	Details
Names	Defibrination syndrome, consumption coagulopathy
Definition	Generalized activation of hemostasis secondary to systemic disease — involves intima, platelets, leukocytes, coagulation, control pathways and fibrinolysis
Forms	Acute, uncompensated (multiple deficiencies; often fatal) vs chronic, compensated (factor/platelet production keeps up)
Presentation	Thrombotic process, but systemic hemorrhage is often the first sign
Chronic DIC causes	Vascular tumors, necrosis, liver/renal disease, chronic inflammation, prosthetic devices, adenocarcinoma (pancreas, prostate, ovary, lung), myeloma, MPNs
Acute DIC causes	Obstetric emergencies, intravascular hemolysis, septicemia, viremia, burns, acute inflammation, crush injury, dissecting aneurysm, cardiac disorders

2.21 Conditions Associated with DIC by Mechanism (Rodak Table 39-14)

Mechanism	Examples
Tissue factor release	Crush/brain injury, surgery, rhabdomyolysis, MI, burns/cold, adenocarcinoma
Subendothelial TF exposure	Hypovolemic/hemorrhagic shock, malignant hypertension, hypoxia, heat stroke, vasculitis
Endotoxins/cytokines	Bacterial, protozoal, fungal, viral septicemia; toxic shock
Immune complexes	HIT with thrombosis, drugs, acute hemolytic transfusion reactions, anaphylaxis, graft rejection
Particulate matter	Eclampsia, preeclampsia, HELLP, retained dead fetus, amniotic fluid embolism, abruptio placentae, uterine rupture, tubal pregnancy, fat embolism
Infusion of activated factors	Activated PCC therapy
Proteolytic enzymes	APL, myelomonocytic leukemia, infections, pancreatitis
Toxins	Snake/spider envenomation, pancreatitis
Thrombotic conditions	TTP, HUS, pregnancy, estrogen, DVT/PE, control-protein deficiencies, purpura fulminans
Hypoxia/acidosis	ACOTS, chronic inflammation, diabetes
Platelet activation	Vascular surgery/bypass, thrombocythemia, polycythemia, vascular tumors, prostheses, aortic aneurysm

2.22 DIC Pathophysiology & Symptoms

Feature	Details
Thrombin	Primary culprit: activates platelets, factors (feedback), fibrin formation → consumes control proteins
Soluble fibrin monomers	Some monomers fail to polymerize → coat platelets/factors → anticoagulant effect
Circulating plasmin	Activated by soluble monomers, polymer and cross-linked fibrin → digests all forms → X, Y, D, E, D-dimer >20,000 ng/mL; digests V, VIII, IX, XI, complement (hemolysis), kinins (hypotension, shock)
Net effect	Thrombin activation + plasmin + loss of PC, PS, AT + thrombocytopenia → hemorrhage
Primary (systemic) fibrinolysis	Plasminogen activated independently (fibrinolytic therapy, amyloidosis, liver disease) → ↓ fibrinogen, FDPs incl. D-dimer, prolonged PT/PTT with normal platelets
Symptoms	Organ failure from microthrombi (renal, ARDS, CNS); skin/bone necrosis; purpura fulminans (meningococcemia, chickenpox, spirochetes)

2.23 DIC Primary Laboratory Profile (Rodak Table 39-15)

Test	Reference	Value in DIC
Platelet count	150,000–450,000/µL	<150,000/µL
PT	11–14 s	>14 s
PTT	25–35 s	>35 s
D-dimer	0–240 ng/mL	>240, often 10,000–20,000 ng/mL (85%)
Fibrinogen	220–498 mg/dL	<220, often higher (acute phase reactant)

2.24 DIC Diagnosis Notes

Feature	Details
Platelets	Film confirms thrombocytopenia in nearly all; schistocytes in ~50%
D-dimer	Essential; also ↑ in inflammation, localized thrombosis, renal disease, sickle crisis, pregnancy — combine with other tests
Normal D-dimer	Rules out DIC and localized VTE (DVT/PE D-dimer >500 ng/mL but not DIC levels)
Fibrinogen	Can be normal/high (acute phase) — unreliable alone
Chronic compensated	Only D-dimer may be elevated

2.25 Specialized DIC Assays (Rodak Table 39-16)

Assay	Value in DIC	Comments
Serum FDP	>10 µg/mL	Obsolete — replaced by D-dimer
Soluble fibrin monomer	Positive	Hemagglutination; avoid protamine sulfate/ethanol gelation
Thrombus precursor protein	>3.5 µg/mL	No interference from fibrinogen/FDPs
Protein C, S, AT activity	<50%	Monitor plasma, AT concentrate, thrombomodulin therapy
Plasminogen, TPA	Decreased	Systemic fibrinolysis
Blood film	Anemia + schistocytes	50% of DIC; leukocytosis common
F1+2, TAT	Elevated	Localized thrombosis; monitor therapy
Factors II, V, VIII, X	<30%	V and VIII rise in inflammation — misleading
Thrombin time, reptilase	Prolonged	Fibrinogen <80, FDPs, soluble monomer

2.26 DIC Treatment

Feature	Details
First	Diagnose and treat the underlying disorder (surgery, antibiotics, obstetric procedures)
Supportive	Fluids, electrolytes
Slow clotting	UFH with care; monitor by chromogenic anti-Xa (PTT ineffective in DIC)
Replace	Thawed plasma; PCC (Kcentra), fibrinogen concentrate, factor VIII concentrate (if TACO concern); platelets if severe; RBCs
Monitor	Fibrinogen, PT, PTT, platelet counts
Antifibrinolytics	Contraindicated except proven systemic fibrinolysis

2.27 Localized Thrombosis Monitors

Feature	Details
F1+2	Released from prothrombin by prothrombinase; half-life 90 min; 0.3–1.5 nmol/L; ↑ VTE; ↓ with heparin/oral anticoagulants
TAT	AT–thrombin covalent complex (heparin enhanced); half-life 3 min; 0.5–5 ng/mL
Specimen	3.2% citrate; centrifuge and separate within minutes; freeze (avoid in vitro activation)
Use	DIC, septicemia, eclampsia, pancreatitis, leukemia, liver disease, trauma; clinical trials

2.28 Heparin-Induced Thrombocytopenia (HIT)

Feature	Details
Cause	1–5% of patients on UFH >5 days develop IgG against heparin–platelet factor 4 complexes; in 30–50%, immune complexes bind platelet Fc receptors → activation, thrombocytopenia, microvascular thrombi
Clinical	Prophylactic or therapeutic doses (more with therapeutic); venous thrombosis 5:1; arterial causes most disturbing events: PE, limb gangrene, stroke, MI; mortality 20%
LMWH	Also causes HIT (mostly cross-reaction after recent UFH; primary ~1% of UFH rate)
Protamine sulfate	May generate similar antibodies
Monitoring	Platelet counts every other day on heparin
Benign (HIT type I)	30% of patients; immediate, limited drop within 1–3 days; small decrease
Thrombotic (HIT type II)	After 5 days (or 1–3 days with recent heparin exposure); drop may exceed 40%; platelets may stay in reference range

2.29 The “4Ts” Scoring System (Rodak Table 39-17)

Indicator	2 points	1 point	0 points
Thrombocytopenia	>50% fall to nadir ≥20,000/µL	30–50% fall (or >50% from surgery), or nadir 10–19,000	<30% fall, or nadir <10,000
Timing	Onset days 5–10, or day 1 with heparin in past 5–30 days	Days 5–10 but unclear; after day 10; or day 1 with exposure 31–100 days	≤4 days without recent heparin
Thrombosis	Proven new thrombosis, skin necrosis, acute systemic reaction	Progressive/recurrent/suspected thrombosis; erythematous skin lesions	None
Other causes	None evident	Possible other cause	Probable other cause

Score: 6–8 high, 4–5 intermediate, 0–3 low probability (max 8). Cardiac-surgery UFH is most immunogenic.

2.30 HIT Laboratory Tests & Treatment

Feature	Details
Immunoassay	Heparin-induced antibody (anti-heparin–PF4) — sensitive; may be positive before clinical signs; false negatives (protamine–PF4), false positives (immune complexes, Ig aggregates); lipemia, hemolysis, contamination interfere
Functional	Aggregometry (only ~50% sensitive); washed platelet lumiaggregometry (more sensitive)
Reference method	¹⁴C-serotonin release assay (SRA) with washed platelets
Treatment	Stop all UFH and LMWH immediately; choose an alternative anticoagulant (stopping all is risky)
Avoid	LMWH (cross-reacts); Coumadin (skin necrosis, too slow)
Use	Argatroban (synthetic DTI) or bivalirudin (leech-based DTI) continuous infusion; fondaparinux in small series
DTI monitoring	PTT, ACT, ecarin clotting time (Echis carinatus venom), plasma-diluted thrombin time (HEMOCLOT)

3 · Visual Memory Hooks

🧠 Venous vs arterial
“Veins get Red fibrin clots (stasis); Arteries get White platelet clots (plaque)”.

🧠 Thrombophilia causes
“Too much Gas, Bad Brakes, or Brakes that can’t Grip” — G20210A, AT/PC/PS, FVL.

🧠 FVL
“Leiden: Arg→Gln at 506 — APC can’t Cut”; ratio <1.8.

🧠 FVL risk
“3× het, 18× homo, 30× with the Pill”.

🧠 Prothrombin mutation
“20210 = Only DNA tells” — no phenotype test.

🧠 Test timing
“AT, PC, PS, LA — wait 14 days off the blood thinner”.

🧠 LA paradox
“LA: Long in the tube, Lethal clots in the body”.

🧠 LA steps
“Screen long → Mix stays long → Phospholipid fixes it → Nothing else explains it”.

🧠 DRVVT
“Dilute Russell’s viper bites factor X”.

🧠 Ratio
“1.2 = the LA line”.

🧠 APL persistence
“Twelve weeks tells chronic from transient”.

🧠 Specimen
“Platelet-poor or LA hides” (<10,000/µL).

🧠 PS types
“Type I all low · Type II only activity low · Type III free low, C4bBP high”.

🧠 Coumadin necrosis
“Protein C drops as fast as VII — skin clots first”.

🧠 Chromogenic AT
“More yellow = Less AT” (inverse).

🧠 Homocysteine
“B₆, B₁₂, Folate keep homocysteine low”; MTHFR alone not a risk.

🧠 Lp(a)
“Lp(a) Pretends to be Plasminogen”.

🧠 DIC
“Clots use up everything, then it Bleeds” — ↓ plts, ↑ PT/PTT, ↑↑ D-dimer, ↓ fibrinogen.

🧠 Primary fibrinolysis
“Fibrinolysis alone spares the Platelets”.

🧠 HIT
“Day 5–10, drop >50%, Clots not bleeds”.

🧠 HIT treatment
“Stop Heparin, Start Argatroban/Bivalirudin — No warfarin, No LMWH”.

🧠 4Ts
“Thrombocytopenia, Timing, Thrombosis, oTher causes”.

Pattern Triggers

If you see…	Think…	Because…
42-year-old woman with PE on IV heparin, workup requested	Test molecular FVL/G20210A and APL immunoassays now; AT/PC/PS/LA ≥14 days off anticoagulants	Rodak case study*
Young woman on OCPs with DVT, sister had PE	Factor V Leiden (double hit)
APC resistance ratio 1.5	Confirm FVL molecularly
Prolonged PTT, no correction on mixing, recurrent miscarriages	Lupus anticoagulant / APS
DRVVT screen ratio 1.6, screen/confirm 1.4	LA confirmed
Positive ACL once after a viral infection, negative at 12 weeks	Transient APL, not significant
Painful necrotic skin lesions days after starting Coumadin	Protein C deficiency — skin necrosis
Heparin given, PTT doesn’t rise	Heparin resistance → AT assay
Newborn with purpura fulminans	Homozygous PC or PS deficiency
Low PS activity, normal total and free antigen	Type II PS deficiency
Low PS activity and free antigen, normal total, high C4bBP	Type III (inflammation)
Migratory thrombophlebitis in older man	Trousseau syndrome — occult adenocarcinoma
Sepsis, oozing IV sites, plts 40, PT/PTT ↑, D-dimer 15,000, fibrinogen 90	Acute DIC
APL patient with bleeding and DIC during chemo	APL-induced DIC
Platelets 250 → 90 on day 7 of heparin, new DVT	HIT (4Ts high)
Platelets 220 → 180 on day 2 of heparin, no thrombosis	Benign (type I) thrombocytopenia
Normal D-dimer in outpatient with low suspicion	Rules out DVT/PE
High HSCRP with high cholesterol	Highest MI risk

*Case answer is my interpretation — the answer key isn’t in the upload.

Commonly Confused Pairs

Feature	A	B
Venous vs arterial thrombosis	Stasis, fibrin, DVT/PE; FVL, AT/PC/PS	Plaque, platelets, MI/stroke; HSCRP, lipids, homocysteine
APC resistance vs FVL	Clot-based phenotype (ratio)	Molecular genotype
LA vs factor inhibitor	Immediate non-correction; corrected by excess phospholipid; thrombosis	Time-dependent (incubation); bleeding
LA vs ACL/anti-β₂-GPI	Clot-based; affected by anticoagulants	Immunoassays; unaffected by heparin/warfarin
Transient vs chronic APL	Infection/drugs; gone by 12 weeks	Persists ≥12 weeks; APS
AT type I vs II	Low activity and antigen	Low activity, normal antigen
Chromogenic vs clot AT	Misses heparin-binding defects	Detects both sites
PS type II vs III	Normal free/total antigen	Low free, normal total, ↑ C4bBP
DIC vs primary fibrinolysis	Low platelets	Normal platelets
DIC vs TTP	Prolonged PT/PTT, ↓ fibrinogen	Normal PT/PTT (Ch. 14)
HIT I vs HIT II	Days 1–3, small drop, benign	Day 5+, >40% drop, thrombosis
F1+2 vs TAT	Prothrombin cleavage; t½ 90 min	AT–thrombin complex; t½ 3 min

Timeline Table

Event	Timing	Key Point	Best Exam Use
AT/PC/PS/LA testing	≥14 days after anticoagulation stops	Avoid false results	Case study
AT, PC, PS low after surgery/thrombosis	10–14 days	Transient decrease	Pitfall
APL repeat	≥12 weeks	Chronic vs transient	APS
LA mixing incubation	37 °C 1–2 h (PTT-based)	Distinguish factor inhibitor	Algorithm
Adult AT levels	By 3 months of age	Pediatric ranges	Reference
CRP rise	6–8 h after inflammation (1000×)	Acute phase	Marker
HIT benign drop	Days 1–3	Type I	HIT
HIT thrombotic	Days 5–10 (day 1 if recent exposure)	Type II	4Ts
Platelet counts on heparin	Every other day	Surveillance	HIT
PE mortality	10–15% within 3 months	Serious	Epidemiology

4 · Diagnostic Flowcharts

Flowchart 1 — Rodak case: hypercoagulability workup during hospitalization

42-year-old woman with PE, on IV heparin	→	Treat — risk factor results don’t change acute therapy
Can test now	→	FVL and prothrombin G20210A (molecular), ACL and anti-β₂-GPI immunoassays
Defer ≥14 days off anticoagulation	→	AT, protein C, protein S activity and LA clot-based assays
Exclude acquired factors	→	OCPs, pregnancy, HRT, immobilization/travel, surgery, fracture, smoking, obesity, cancer, APS, nephrotic syndrome, MPN, PNH, catheter
Congenital factor found	→	Longer anticoagulation, avoid estrogen, prophylaxis in high-risk situations, family testing/counseling
⚠️ Common mistake: running AT/PC/PS during acute thrombosis on heparin — results are falsely low.

Flowchart 2 — Prolonged PTT mixing study (Figure 39-1)

PTT prolonged	→	Thrombin time
TT prolonged	→	Hepzyme → repeat PTT: normal = heparin
Immediate 1:1 mix uncorrected	→	Lupus anticoagulant workup
Immediate corrects → incubated 37 °C 1–2 h	→	Corrects = factor deficiency; uncorrected = specific inhibitor
⚠️ Common mistake: calling every uncorrected mix a factor VIII inhibitor — LA is far more common and causes thrombosis.

Flowchart 3 — LA confirmation (Figure 39-3)

DRVVT screen ratio (patient/NP)	→	>1.2 → DRVVT confirm (high PL)
Screen/confirm ratio >1.2	→	LA confirmed
DRVVT ≤1.2 either step	→	Silica low-PL PTT screen → >1.2 → PTT confirm
PTT screen/confirm >1.2	→	LA; otherwise negative
Positive	→	Repeat after 12 weeks + ACL/anti-β₂-GPI
⚠️ Common mistake: using platelet-rich plasma — platelet phospholipid neutralizes LA (false negative).

Flowchart 4 — APL immunoassays (Figure 39-4)

ACL and anti-β₂-GPI	→	Positive → repeat after 12 weeks
Both negative	→	Antiphosphatidylserine (APTS) assay
APTS negative	→	No APL
Repeat positive at 12 weeks	→	Chronic, clinically significant APL
Repeat negative	→	Transient, not significant
⚠️ Common mistake: diagnosing APS from a single positive result.

Flowchart 5 — Suspected DIC

Underlying trigger (sepsis, obstetric, trauma, cancer, APL)	→	Platelets, film, PT, PTT, fibrinogen, D-dimer
↓ Platelets, ↑ PT/PTT, ↑↑ D-dimer, ↓ fibrinogen	→	Acute DIC
Only D-dimer ↑	→	Chronic compensated DIC
↓ Fibrinogen, ↑ FDP/D-dimer, ↑ PT/PTT, normal platelets	→	Primary fibrinolysis
Treat	→	Underlying cause; plasma, cryo/fibrinogen, platelets; UFH (anti-Xa); no antifibrinolytics
⚠️ Common mistake: excluding DIC because fibrinogen is normal — it’s an acute phase reactant.

Flowchart 6 — Suspected HIT

Platelet fall on heparin	→	Calculate 4Ts
Low (0–3)	→	HIT unlikely — look for other causes
Intermediate/high (4–8)	→	Stop UFH/LMWH; start argatroban or bivalirudin
Lab	→	Anti-heparin–PF4 immunoassay → SRA (reference) if needed
Avoid	→	LMWH, Coumadin (until platelets recover), platelet transfusions
⚠️ Common mistake: just stopping heparin without an alternative anticoagulant — thrombosis continues.

*’Until platelets recover’ and platelet-transfusion caution are general clinical knowledge.

5 · 25 High-Yield Facts

#	Fact
1	Thrombophilia is a predisposition to thrombosis secondary to a congenital or acquired disorder.
2	The annual incidence of venous thromboembolism in the United States is about 1 in 1000.
3	Nearly 95% of pulmonary emboli arise from deep leg and calf vein thrombi.
4	Arterial thrombosis mostly results from rupture of unstable atherosclerotic plaque (white thrombi).
5	Oral contraceptives increase thrombosis risk 4–6 times; pregnancy 3–5 times.
6	Trousseau syndrome is low-grade chronic DIC associated with adenocarcinoma.
7	Factor V Leiden (R506Q) is the most common inherited thrombophilia (3–8% of Caucasians).
8	An APC resistance ratio <1.8 indicates APC resistance; it is confirmed by molecular FVL testing.
9	Factor V Leiden heterozygotes on oral contraceptives have about a 30-fold increase in thrombosis risk.
10	Prothrombin G20210A is a 3′ UTR mutation detectable only by molecular assay.
11	AT, protein C, protein S and LA assays should be done at least 14 days after anticoagulation stops.
12	Lupus anticoagulant is detected by a phospholipid-dependent screen, lack of correction on mixing, and correction with excess phospholipid.
13	The DRVVT is the primary LA screening test because it has the fewest interferences.
14	LA testing requires platelet-poor plasma (<10,000/µL).
15	Positive APL antibody results must be repeated after 12 weeks to establish persistence.
16	Anti-β₂-GPI >20 units correlates with thrombosis better than ACL.
17	Chromogenic AT color intensity is inversely proportional to AT activity.
18	Heparin resistance can be caused by antithrombin deficiency.
19	Coumadin-induced skin necrosis occurs in protein C deficiency because PC falls as fast as factor VII.
20	Type I PS deficiency has low activity, free and total antigen with normal C4bBP.
21	Lipoprotein (a) promotes thrombosis by competing with plasminogen on fibrin.
22	DIC shows thrombocytopenia, prolonged PT/PTT, markedly increased D-dimer and often decreased fibrinogen.
23	A normal D-dimer rules out DIC and venous thromboembolism.
24	HIT is caused by IgG against heparin–PF4 complexes and usually begins 5–10 days after heparin starts.
25	HIT is treated by stopping all heparin and using a direct thrombin inhibitor such as argatroban.

⭐ EXAM TIP — The single most testable pattern

APC resistance ratio <1.8 → FVL molecular. LA: prolonged screen + no mix correction + corrected by high phospholipid (DRVVT first, ratio 1.2); repeat APL at 12 weeks. Test AT/PC/PS/LA ≥14 days off anticoagulants. DIC: ↓ plts, ↑ PT/PTT, ↑↑ D-dimer. HIT: day 5–10 drop >50% + clots → stop heparin, give argatroban.

Quick Interpretation Table

Lab Finding	Clinical Interpretation
42-year-old woman, PE, on IV heparin, workup requested	Now: FVL, G20210A, ACL, anti-β₂-GPI; later (≥14 days off): AT, PC, PS, LA; exclude OCP/pregnancy/immobility/cancer; congenital result → counseling, anticoagulation duration, family testing (Rodak case study)*
PS activity, antigen and free antigen <65%, C4bBP normal	Type I PS deficiency (Rodak Q7)
APC resistance ratio 1.4, FVL heterozygous	Factor V Leiden — 3× risk
DRVVT screen 1.5, confirm corrects	Lupus anticoagulant — repeat in 12 weeks
AT activity 45%, AT antigen 90%	Type II AT deficiency (if repeated off anticoagulants)
Plts 45, PT 19, PTT 52, fibrinogen 95, D-dimer 18,000	Acute DIC
Fibrinogen 80, D-dimer ↑, PT/PTT ↑, platelets normal, after thrombolytic therapy	Primary fibrinolysis
4Ts score 7, positive anti-PF4 immunoassay	HIT — stop heparin, start argatroban

*Case answers are my interpretation — answer key not in the upload.

🎴 Flashcards — Active Recall Practice

How it works: tap the card to flip it. Then mark it ✓ Knew It or ✗ Review Again (buttons unlock after flipping). Use 🔀 Shuffle to randomize and 🏁 Finish anytime — your summary appears at the end, and you can drill only the cards you missed.

📝 Practice Quiz — Test Your Knowledge

How it works: tap an answer for each case. You’ll get instant feedback with the full explanation and the examiner’s trap. Your final score appears once all 10 are answered.

🪤 Trap Questions — Beat the Examiner

Harder on purpose. Each question targets a real misconception. After answering you’ll see the correct reasoning, the trap explained, why the examiner wrote it, and the wrong answer most students choose.

8 · Rapid Revision Sheet

📖 READ THIS 2 HOURS BEFORE YOUR EXAM

Basics

Thrombophilia = congenital or acquired predisposition
VTE 1/1000/yr; 95% PE from legs
Arterial: plaque, platelets (white)
OCP 4–6× · pregnancy 3–5× · HRT 2–4×
Double hit: FVL + OCP 30×

Congenital

FVL R506Q: 3–8% Caucasians; 3× / 18×
G20210A: 3′ UTR; molecular only
AT def 10–20× · PC 2–5× · PS 1.6–11.5×
Homozygous PC/PS → purpura fulminans
Suspect: young, unusual site, recurrent, family

APC Resistance

Patient 1:4 V-depleted plasma + PTT
± APC + CaCl₂ → ratio
Normal ≥1.8; APCR <1.8
LA interferes → go molecular
Platelet-poor plasma

Lupus Anticoagulant

Screen → no mix correction → high PL corrects
DRVVT (X) primary + low-PL PTT (XII)
Ratio >1.2
Platelet-poor <10,000/µL
Transient vs chronic: repeat 12 wk

APL Immunoassays

ACL: GPL/MPL; 60% with LA
Anti-β₂-GPI >20 U best correlates
APTS if others negative
Not affected by heparin/warfarin
Drugs: procainamide, hydralazine, phenytoin…

AT, PC, PS

Test ≥14 days off anticoagulants
AT 78–126%; chromogenic inverse color
AT type I 90%; heparin resistance
PC chromogenic Protac; skin necrosis
PS types I/II/III (C4bBP)

Arterial Predictors

HSCRP 0.3–1.7 mg/L; ≥1.5 risk
Homocysteine: B₆, B₁₂, folate; MTHFR not independent
Fibrinogen quintiles 1 → 2.9×
Lp(a) competes with plasminogen
↑ PAI-1 arterial risk

DIC

Consumption: ↓ plts, ↑ PT/PTT, ↑↑ D-dimer
Fibrinogen may be normal (acute phase)
Schistocytes ~50%
Chronic: D-dimer only
Primary fibrinolysis: platelets normal

DIC Causes & Rx

Sepsis, obstetric, trauma, burns, APL, cancer
Activated PCC, snake venom, transfusion reaction
Treat cause; plasma, cryo, platelets
UFH via anti-Xa
No antifibrinolytics

HIT

IgG vs heparin–PF4; 1–5% UFH >5 d
Days 5–10; >50% drop; VTE 5:1; 20% mortality
4Ts: 6–8 high
Immunoassay → SRA reference
Stop heparin; argatroban/bivalirudin; no LMWH/Coumadin

9 · Final Memory Map

🧊 THROMBOTIC DISORDERS
- Thrombosis Basics
  - Venous vs arterial · thrombophilia definition
  - Epidemiology
- Acquired Risk
  - Lifestyle: age, immobility, OCP, pregnancy, surgery
  - Disease: APS, MPN, cancer (Trousseau), PNH, liver, nephrotic
- Congenital Risk
  - FVL · G20210A · AT · PC · PS
  - Double hit
- Lab Evaluation
  - APC resistance/FVL · G20210A molecular
  - LA algorithm · ACL · anti-β₂-GPI · APTS
  - AT, PC, PS assays and timing
- Arterial Predictors
  - HSCRP · homocysteine · fibrinogen · Lp(a) · lipids
- Consumption & Drug-Induced
  - DIC: causes, profile, treatment
  - TAT and F1+2
  - HIT: 4Ts, lab, argatroban