Understand primary and secondary hemostasis, coagulation cascade, and clot formation for ASCP hematology.

ASCPprep.com | Hematology & Hemostasis

Chapter 23 โ€” NORMAL HEMOSTASIS AND COAGULATION

ASCP Board Exam ยท Lab-Focused Study Guide
Primary vs Secondary Hemostasis ยท Vascular Intima (Anticoagulant & Procoagulant) ยท Platelet Adhesion, Aggregation, Secretion ยท Coagulation Factors & Nomenclature ยท Vitamin K ยท Coagulation Complexes ยท Extrinsic/Intrinsic/Common Pathways ยท Cell-Based Model ยท Thrombin ยท Fibrin Formation ยท TFPI, Protein C/S, Antithrombin, ZPI ยท Fibrinolysis & D-Dimer ยท Practice Questions

1 ยท Priority Table & Quick Foundation

Topic Priority Why It’s Tested
Factor names, numbers, functions (serine protease vs cofactor vs transglutaminase) HIGH Table 37-5; constant exam material
Extrinsic, intrinsic and common pathways; PT vs PTT HIGH Test interpretation foundation
Coagulation complexes: extrinsic tenase, intrinsic tenase, prothrombinase HIGH Rodak Q6
Vitamin K: ฮณ-carboxylation of II, VII, IX, X, C, S, Z; warfarin; PIVKAs HIGH Rodak Q4
Platelet adhesion (VWFโ€“GP Ib/IX/V) and aggregation (fibrinogenโ€“GP IIb/IIIa) HIGH Rodak Q3; Bernard-Soulier vs Glanzmann
Thrombin’s roles; fibrinogen โ†’ fibrin โ†’ cross-linked fibrin (XIIIa) HIGH Rodak Q5
Regulators: TFPI, protein C/S (APC inactivates Va, VIIIa), antithrombin + heparin HIGH Rodak Q8; case study
Fibrinolysis: TPA, plasmin, PAI-1, ฮฑโ‚‚-antiplasmin, TAFI; FDPs vs D-dimer HIGH Rodak Q7
Vascular intima: prostacyclin, NO, thrombomodulin, VWF (Weibel-Palade), TF MEDIUM Rodak Q1, Q2
Factor half-lives (VII 6 h, VIII 12 h, II 60 h) and warfarin onset MEDIUM Therapy monitoring
Cell-based model: initiation vs propagation, COAT-platelets MEDIUM Modern concept
Aspirin/COX-1/thromboxane Aโ‚‚ pathway; granule contents MEDIUM Platelet pharmacology
Contact factors (XII, pre-K, HMWK) โ€” prolonged PTT without bleeding MEDIUM Classic trap
๐ŸŽฏ KEY POINT โ€” Where to spend your time

Focus: factor functions and pathways, PT/PTT mapping, the three complexes, vitamin K factors, platelet receptors, thrombin’s jobs, fibrin formation, protein C/S and antithrombin, fibrinolysis and D-dimer. Skim: exact molecular weights and plasma concentrations, vitamin K food list, ICAM/PECAM details.

Quick Foundation โ€” from zero

  • Hemostasis keeps blood fluid inside vessels, plugs holes when injured, and removes the plug as the wound heals. Too little โ†’ bleeding; too much โ†’ thrombosis.
  • Primary hemostasis (secondsโ€“minutes): vessel constriction + platelet plug (adhesion, aggregation, secretion).
  • Secondary hemostasis (delayed, lasting): a chain of plasma coagulation factors (mostly liver-made enzymes) ends with thrombin turning fibrinogen into a fibrin net that reinforces the plug.
  • Regulators (TFPI, protein C/S, antithrombin) keep clotting local; fibrinolysis (plasmin) dissolves the clot later.
  • Lab tests: PT checks the extrinsic + common pathway; PTT checks the intrinsic + common pathway.
๐Ÿ’ก Analogy

Think of a burst water pipe. Vasoconstriction = turning down the valve. Platelets = duct tape slapped on the hole (fast but weak). The coagulation cascade = a crew mixing concrete (fibrin) to seal it permanently โ€” each worker activates the next, amplifying the job. Regulators = the foreman stopping them from concreting the whole street. Fibrinolysis = the demolition crew that removes the patch once the pipe is repaired. D-dimer = the rubble proving concrete was poured and broken up.

๐Ÿฅ Why this matters clinically

Every coagulation test the lab runs โ€” PT/INR, PTT, fibrinogen, factor assays, D-dimer, anti-Xa โ€” maps to a step in this chapter. Missing a single procoagulant can mean lifelong bleeding (hemophilia); missing a single inhibitor can mean recurrent thrombosis (protein C/S or antithrombin deficiency, as in the case study).

Concept Plain-English Explanation
Zymogen Inactive enzyme precursor (e.g., factor X โ†’ Xa)
Serine protease Enzyme cutting peptide bonds with an active-site serine (IIa, VIIa, IXa, Xa, XIa, XIIa, kallikrein)
Cofactor Non-enzyme helper that speeds its enzyme (TF, V, VIII, HMWK)
Tenase / prothrombinase Membrane enzyme complexes activating X / prothrombin
ฮณ-Carboxylation Vitamin Kโ€“dependent step that lets factors bind Caยฒโบ and phospholipid
Serpin Serine protease inhibitor (antithrombin, ZPI, ฮฑโ‚‚-antiplasmin, PAI-1)
Fibrinolysis Plasmin-mediated digestion of fibrin
D-dimer Two cross-linked D domains โ€” proves fibrin was formed and lysed

2 ยท Core Content Tables

2.1 Primary vs Secondary Hemostasis (Rodak Table 37-1)

Primary Hemostasis Secondary Hemostasis
Activated by desquamation and small vessel injuries Activated by large injuries to vessels and surrounding tissues
Vascular intima and platelets Platelets and coagulation system
Rapid, short-lived response Delayed, long-term response
Procoagulants exposed/released by damaged or activated endothelial cells Activator (tissue factor) exposed on cell membranes
Defects: collagen disorders, thrombocytopenia, platelet disorders, VWD Defects: factor deficiencies (hemophilia)

2.2 Vascular Intima Structure (Box 37-1)

Feature Details
Innermost lining Endothelial cells (ECs) โ€” metabolically active monolayer
Support Internal elastic lamina (elastin + collagen)
Subendothelial connective tissue Collagen and fibroblasts (veins); + smooth muscle cells (arteries/arterioles โ€” contract in primary hemostasis)

2.3 Intact vs Damaged Endothelium (Box 37-2, Table 37-2)

Intact Endothelium โ€” Anticoagulant Damaged Intima โ€” Procoagulant
Smooth, contiguous rhomboid cells Vasoconstriction (smooth muscle in arteries/arterioles)
Prostacyclin (PGIโ‚‚) โ€” platelet inhibitor and vasodilator Exposed subendothelial collagen binds VWF and platelets
Nitric oxide โ€” smooth muscle relaxation, inhibits platelets ECs secrete VWF from Weibel-Palade bodies
Heparan sulfate โ€” enhances antithrombin ECs express P-selectin, ICAMs, PECAMs
TFPI โ€” controls extrinsic (TF) pathway Exposed smooth muscle cells/fibroblasts: tissue factor
Thrombomodulin and EPCR โ€” protein C activation Inflammation induces TF on ECs/monocytes
Secretes TPA โ†’ fibrinolysis PAI-1 and TAFI slow fibrinolysis; ADAMTS-13 trims VWF

2.4 Platelet Function (Rodak Table 37-3)

Function Characteristics Key Molecules
Adhesion โ€” bind non-platelet surfaces Reversible; seals endothelial gaps; VWF necessary in arterioles (high shear) VWF โ†” GP Ib/IX/V; collagen directly in veins/capillaries. Absent GP Ib/IX/V = Bernard-Soulier; missing VWF = VWD
Aggregation โ€” platelets bind each other Irreversible; plug forms; requires fibrinogen and Caยฒโบ Fibrinogen โ†” GP IIb/IIIa (also VWF, fibronectin). Absent GP IIb/IIIa = Glanzmann thrombasthenia; afibrinogenemia
Secretion โ€” discharge granules Irreversible; mostly late in activation; essential to coagulation ฮฑ-granules and dense bodies

In vitro aggregation agonists: thrombin (TRAP), arachidonic acid, ADP, collagen, epinephrine.

2.5 Platelet Granule Contents (Rodak Table 37-4)

ฮฑ-Granules (large molecules) Dense Granules (small molecules)
ฮฒ-Thromboglobulin ADP (activates neighboring platelets)
Factor V ATP
Factor XI Calcium
Protein S Serotonin (vasoconstrictor)
Fibrinogen
VWF
Platelet factor 4 (heparin inhibitor)
Platelet-derived growth factor

2.6 Arachidonic Acid Pathway & Aspirin

Feature Details
Pathway ADP and Caยฒโบ activate phospholipase Aโ‚‚ โ†’ membrane phospholipid โ†’ arachidonic acid โ†’ cyclooxygenase-1 โ†’ PGGโ‚‚/PGHโ‚‚ โ†’ thromboxane synthase โ†’ thromboxane Aโ‚‚
TXAโ‚‚ effects Caยฒโบ release, platelet aggregation, vasoconstriction
Aspirin Acetylates COX-1 permanently โ†’ no TXAโ‚‚ for the platelet’s life (aspirin effect)
Measurable product Thromboxane Bโ‚‚ โ€” stable plasma product, reduced on aspirin
Platelet surface role Supplies Caยฒโบ, phosphatidylserine, procoagulant factors and receptors for complex assembly
Other cells RBCs add bulk (bleeding tendency in anemia); monocytes/lymphocytes express TF in inflammation

2.7 Plasma Procoagulants (Rodak Table 37-5)

Factor Name Function Half-Life (h) Plasma Conc.
I Fibrinogen Thrombin substrate; polymerizes to fibrin 100โ€“150 200โ€“400 mg/dL
II Prothrombin Serine protease 60 10 mg/dL
III Tissue factor Cofactor Insoluble None
IV Ionic calcium Mineral NA 8โ€“10 mg/dL
V Labile factor Cofactor 24 1 mg/dL
VII Stable factor Serine protease 6 (shortest) 0.05 mg/dL
VIII Antihemophilic factor Cofactor 12 0.01 mg/dL
VWF von Willebrand factor VIII carrier, platelet adhesion 24 1 mg/dL
IX Christmas factor Serine protease 24 0.3 mg/dL
X Stuart-Prower factor Serine protease 48โ€“52 1 mg/dL
XI Plasma thromboplastin antecedent (PTA) Serine protease 48โ€“84 0.5 mg/dL
XII Hageman factor Serine protease 48โ€“70 3 mg/dL
Prekallikrein Fletcher factor Serine protease 35 35โ€“50 ยตg/mL
HMWK Fitzgerald factor Cofactor 156 5 mg/dL
XIII Fibrin-stabilizing factor Transglutaminase (transamidase) 150 2 mg/dL
Platelet factor 3 Phospholipids (phosphatidylserine) Assembly molecule Released by platelets โ€”

2.8 Nomenclature Rules

Feature Details
Naming ICSN 1958: Roman numerals in order of discovery; activated form adds ‘a’ (VIIa)
By name Factor I fibrinogen, II prothrombin, III tissue factor, IV calcium โ€” usually called by name
Factor VI Assigned to activated V โ€” withdrawn, never reassigned
No numerals Prekallikrein (Fletcher) and HMWK (Fitzgerald) โ€” belong to kallikrein/kinin systems
Liver Nearly all factors made in the liver (some by monocytes, ECs, megakaryocytes)

2.9 Serine Proteases & Cofactors (Tables 37-6, 37-9)

Zymogen โ†’ Active Cofactor Substrate
Prothrombin (II) โ†’ thrombin (IIa) โ€” Fibrinogen, V, VIII, XI, XIII
VII โ†’ VIIa Tissue factor IX, X
IX โ†’ IXa VIIIa X
X โ†’ Xa Va Prothrombin
XI โ†’ XIa โ€” IX
XII โ†’ XIIa HMWK XI
Prekallikrein โ†’ kallikrein HMWK XI*

Other procoagulants (Box 37-3): fibrinogen, factor XIII, phospholipids, calcium, VWF. Control cofactors: thrombomodulin (binds thrombin; protein C + TAFI), protein S (protein C, TFPI), protein Z (ZPI). *Table 37-6 lists XI; kallikrein classically activates XII (reciprocal activation) โ€” general knowledge.

2.10 Vitamin Kโ€“Dependent Proteins (Table 37-7)

Feature Details
Procoagulants Prothrombin (II), VII, IX, X โ€” the ‘prothrombin group’
Regulators Protein C, protein S, protein Z
Structure 10โ€“12 glutamic acids near the amino terminus; all except S and Z are serine proteases (S and Z = cofactors)
Sources Green leafy vegetables (kale, spinach, broccoliโ€ฆ); gut bacteria Bacteroides fragilis and E. coli
Mechanism Vitamin Kโ€“dependent carboxylase adds a second carboxyl to the ฮณ carbon: Glu โ†’ ฮณ-carboxyglutamic acid (Gla) โ†’ negative pocket binds Caยฒโบ โ†’ binds phospholipid (phosphatidylserine)
Recycling Vitamin K hydroquinone โ†’ epoxide (during carboxylation) โ†’ back via epoxide reductase
Warfarin Inhibits epoxide reductase โ†’ des-ฮณ-carboxyl proteins = PIVKAs โ†’ cannot bind Caยฒโบ/phospholipid โ†’ nonfunctional
Warfarin timing VII falls within ~6 h, but prothrombin takes 4โ€“5 days โ†’ full effect after ~5 days

2.11 Coagulation Complexes (Rodak Table 37-8)

Complex Components Activates Surface
Extrinsic tenase VIIa, tissue factor, phospholipid, Caยฒโบ IX and X TF-bearing cell
Intrinsic tenase IXa, VIIIa, phospholipid, Caยฒโบ X (50โ€“100ร— faster than extrinsic) Activated platelet
Prothrombinase Xa, Va, phospholipid, Caยฒโบ Prothrombin โ†’ thrombin + fragment 1.2 Activated platelet (>300,000ร— faster than Xa alone)

Prothrombin fragment 1.2 in plasma is a marker of thrombin generation. Complexes on membranes are protected from inhibitors.

2.12 Key Individual Factors

Feature Details
Tissue factor Transmembrane receptor for VIIa on fibroblasts, smooth muscle; not on normal ECs; high in brain, lung, placenta, heart, kidney, testes; induced on leukocytes in inflammation/sepsis
Factor V Plasma + platelet ฮฑ-granules; activated by thrombin, inactivated by APC (Va โ†’ Vi)
Factor VIII 260,000 Da; hepatocytes + microvascular ECs; circulates bound to VWF; thrombin releases and activates it; inactivated by APC; deteriorates fastest in stored plasma (~50% after 5 days); replacement every 12 h
X-linked factors VIII (hemophilia A) and IX (hemophilia B)
VWF Subunits 240,000 Da โ†’ multimers 0.6โ€“20 million Da; made by ECs and megakaryocytes; stored in platelet ฮฑ-granules and Weibel-Palade bodies; 7โ€“10 ยตg/mL; ADAMTS-13 cleaves ultralarge multimers (deficient in TTP)
VWF binding sites GP Ib/IX/V (adhesion), GP IIb/IIIa via RGD (aggregation), collagen, factor VIII
VWF levels VWD in 1โ€“2% of population; group O lower VWF; acute phase reactant (pregnancy, inflammation, stress)
Contact factors XII, prekallikrein (Fletcher), HMWK (Fitzgerald) โ€” activated by negative surfaces (glass, kaolin, ellagic acid in PTT; stents, valves in vivo). XIIa: pre-K โ†’ kallikrein โ†’ HMWK โ†’ bradykinin. Deficiency prolongs PTT but causes no bleeding
Factor XI Activated by contact complex and by thrombin; XIa activates IX; deficiency (Rosenthal syndrome) โ†’ mild, variable bleeding
Therapeutic level Most factors hemostatic at 25โ€“30%

2.13 Thrombin โ€” The Key Protein

Feature Details
1. Fibrin formation Cleaves fibrinopeptides A and B from fibrinogen
2. Amplification Activates cofactors V, VIII and factor XI (positive feedback)
3. Stabilization Activates XIII โ†’ cross-linked fibrin
4. Platelet activation Cleaves PAR-1 and PAR-4
5. Anticoagulation Bound to thrombomodulin โ†’ activates protein C
6. Antifibrinolysis Thrombin-thrombomodulin activates TAFI

2.14 Fibrinogen & Fibrin Formation

Feature Details
Fibrinogen 340,000 Da liver glycoprotein; 200โ€“400 mg/dL โ€” most concentrated procoagulant; acute phase reactant; also links platelets via GP IIb/IIIa
Structure Mirror-image trinodular dimer; each half Aฮฑ, Bฮฒ, ฮณ (disulfide-linked); N-termini โ†’ central E domain; C-termini โ†’ two D domains
Step 1 Thrombin cleaves fibrinopeptides A and B (from ฮฑ and ฮฒ chains in the E domain) โ†’ fibrin monomer (MW โ†“ 10,000)
Step 2 Exposed E domains bind D domains of neighbors โ†’ spontaneous fibrin polymer
Step 3 XIIIa (transglutaminase; ฮฑ subunit from megakaryocytes/monocytes, ฮฒ from liver) covalently cross-links ฮณ chains of adjacent D domains (ฮต-amino lysine + ฮณ-amide glutamine) โ†’ insoluble stabilized fibrin; incorporates fibronectin, ฮฑโ‚‚-antiplasmin, plasminogen, TPA
Clot assay endpoint Fibrinopeptide cleavage at end of initiation (10โ€“30 nmol/L thrombin, ~3% of total)

2.15 Plasma-Based (In Vitro) Pathways

Pathway Factors Screening Test Notes
Extrinsic (tissue factor pathway) TF, VII, then X, V, II, I PT Primary in vivo initiator (TF:VIIa)
Intrinsic XII, pre-K, HMWK, XI, IX, VIII, then X, V, II, I PTT (APTT) Contact factors not significant in vivo; IX:VIII crucial (hemophilia A/B)
Common X, V, II (prothrombin), I (fibrinogen) PT and PTT Converge at factor X

XIII is not detected by PT or PTT (clot forms normally)*. *General knowledge; Rodak doesn’t state it in this chapter.

2.16 Cell-Based (In Vivo) Coagulation

Feature Details
Concept Pathways are interdependent; need TF-bearing cells (extravascular) + platelets (intravascular)
Initiation On TF-bearing cells; 1โ€“2% of VII circulates as VIIa but is inert until bound to TF; TF:VIIa activates small amounts of IX and X; Xa:Va makes a little thrombin (3โ€“5% of total)
Initiation thrombin roles (1) Activates platelets (PAR-1, PAR-4) ยท (2) activates V ยท (3) activates VIII and frees it from VWF ยท (4) activates XI ยท (5) cleaves fibrinopeptides
Protection Membrane-bound complexes protected; free Xa quickly inhibited by TFPI, AT, ZPI
Propagation On activated platelets (COAT-platelets โ€” collagen + thrombin); IXa:VIIIa + Xa:Va โ†’ thrombin burst (โ‰ฅ95%); fibrin, XIII, protein C, TAFI
Localization Requires TF cells + activated platelets โ†’ clotting stays at the injury
Bleeding disorders Deficiency of VII, IX, VIII, X, V or prothrombin compromises thrombin generation

2.17 Coagulation Regulatory Proteins (Rodak Table 37-10)

Name Function Half-Life Plasma Concentration
TFPI With Xa, binds TF:VIIa Unknown 60โ€“80 ng/mL
Thrombomodulin EC surface receptor for thrombin Does not circulate None
Protein C Serine protease 7โ€“9 h 2โ€“6 ยตg/mL
Protein S Cofactor Unknown 20โ€“25 ยตg/mL
Antithrombin Serpin 68 h 24โ€“40 mg/dL
Heparin cofactor II Serpin (mainly thrombin) 60 h 30โ€“70 ยตg/dL
Z-dependent protease inhibitor Serpin Unknown 1.5 ยตg/mL
ฮฑโ‚-Protease inhibitor Serpin Unknown 250 mg/dL
ฮฑโ‚‚-Macroglobulin Serpin 60 h 150โ€“400 mg/dL

2.18 Tissue Factor Pathway Inhibitor (TFPI)

Feature Details
Type Kunitz-type serine protease inhibitor; main regulator of the TF pathway; made by ECs, also on platelets
Mechanism Kunitz-2 binds and inhibits Xa; TFPI:Xa then binds TF:VIIa (quaternary complex) โ€” or binds Xa within TF:VIIa:Xa
Feedback Only acts after X is activated โ†’ extrinsic tenase short-lived โ†’ propagation shifts to intrinsic (IXa:VIIIa, XIa)
Cofactor Protein S enhances TFPI inhibition of Xa tenfold

2.19 Protein C Regulatory System

Feature Details
Trigger Thrombin binds EC thrombomodulin โ†’ switches from procoagulant to anticoagulant
Activation Thrombin-thrombomodulin activates protein C; EPCR binds PC/APC and boosts activation โ‰ฅ5ร—
Action APC + free protein S hydrolyze and inactivate Va (โ†’ Vi) and VIIIa (โ†’ VIIIi)
Protein S forms ~40% free (active cofactor), ~60% bound to C4b-binding protein (inactive). C4bBP is an acute phase reactant โ†’ inflammation lowers free protein S โ†’ thrombosis risk
Deficiencies Protein C, protein S, or factor V mutations โ†’ recurrent venous thromboembolism
Homozygous protein C deficiency Neonatal purpura fulminans โ€” fatal without protein C replacement and anticoagulation

2.20 Antithrombin & Other Serpins

Feature Details
Antithrombin (AT) First regulator identified; serpin neutralizing thrombin (IIa), IXa, Xa, XIa, XIIa, prekallikrein, plasmin
Heparin Accelerates AT ~2000-fold; in vivo from mast cells and EC heparan sulfate
Unfractionated heparin >18 sugar units โ€” bridges AT and thrombin (pentasaccharide sequence) โ†’ inactivates thrombin and Xa
LMWH / pentasaccharide Too short to bridge โ†’ AT preferentially inactivates Xa
TAT complex AT covalently binds thrombin โ†’ thrombin-antithrombin complex measurable marker of coagulation activation
Heparin cofactor II Primarily inactivates thrombin; needs heparin
ZPI + protein Z Protein Z (vitamin Kโ€“dependent, nonproteolytic cofactor) increases ZPI inhibition of Xa 2000-fold (needs Caยฒโบ, phospholipid); ZPI also inhibits XIa (without protein Z)
Protein C inhibitor Nonspecific: APC, thrombin, Xa, XIa, urokinase โ€” anticoagulant, procoagulant or antifibrinolytic depending on target
ฮฑโ‚-antitrypsin, ฮฑโ‚‚-macroglobulin Reversible serine protease inhibitors

2.21 Proteins of the Fibrinolysis Pathway (Rodak Table 37-11)

Name Function Half-Life Plasma Concentration
Plasminogen Zymogen โ†’ plasmin digests fibrin/fibrinogen 24โ€“26 h 15โ€“21 mg/dL
TPA Secreted by activated endothelium; activates plasminogen Unknown 4โ€“7 ยตg/dL
Urokinase (UPA) Secreted by kidney (urinary epithelium, monocytes, macrophages); activates plasminogen Unknown 2โ€“4 ng/mL
PAI-1 Secreted by endothelium; inhibits TPA (and UPA) 1 h 14โ€“28 mg/dL*
ฮฑโ‚‚-Antiplasmin Inhibits free plasmin Unknown 7 mg/dL
TAFI Removes fibrin C-terminal lysines โ†’ blocks plasminogen/TPA binding 8โ€“10 min 5 ยตg/mL

*Value as printed in Rodak Table 37-11; PAI-1 is usually quoted in ng/mL in other references.

2.22 Fibrinolysis โ€” Mechanism & Control

Feature Details
Timing Begins a few hours after fibrin polymerization and cross-linking
Localization Plasminogen, TPA, UPA and PAI-1 bind fibrin lysine via kringle loops โ†’ concentrated in the clot
Plasminogen 92,000 Da liver zymogen; 5 kringles; cleaved Arg561โ€“Val562 โ†’ two-chain plasmin
Plasmin Digests fibrin (arginine/lysine bonds); exposed C-terminal lysines recruit more plasminogen/TPA. Free plasmin digests fibrinogen, V, VIII, fibronectin โ†’ potentially fatal primary fibrinolysis โ€” normally neutralized by ฮฑโ‚‚-antiplasmin
TPA ECs; two kringles; lysine bonds to fibrin; recombinant TPA dissolves pathologic clots
UPA One kringle, binds fibrin weakly; minor physiologic role; therapeutic use
PAI-1 Principal inhibitor of plasminogen activation (TPA and UPA); from ECs, megakaryocytes, smooth muscle, fibroblasts, hepatocytes etc.; platelets store >half; fibrin-bound TPA is protected. Deficiency โ†’ mild bleeding; โ†‘ (acute phase, metabolic syndrome, obesity, sepsis) โ†’ thrombosis
ฮฑโ‚‚-Antiplasmin Liver serpin; primary inhibitor of free plasmin; N-terminus cross-linked to fibrin by XIIIa; C-terminal lysine competes for plasmin kringles
Lysine analogues Tranexamic acid and ฮต-aminocaproic acid โ†’ antifibrinolytic
TAFI Liver procarboxypeptidase activated by thrombin-thrombomodulin; hemophilia โ†’ less TAFI โ†’ more lysis/bleeding; thrombosis โ†’ more TAFI

2.23 Fibrin Degradation Products & D-Dimer

Feature Details
From fibrinogen or fibrin Plasmin produces X (D-E-D), Y (D-E), then D and E fragments; some inhibit platelets and fibrin polymerization โ†’ bleeding
D-dimer Two D domains from separate fibrin molecules cross-linked by XIIIa โ€” only from cross-linked fibrin
Meaning Marker of thrombosis and fibrinolysis (thrombin, XIIIa and plasmin all activated)
Testing Monoclonal antibody immunoassays (quantitative, point-of-care whole blood)
Uses Identify acute/chronic DIC; rule out venous thromboembolism (DVT/PE)

3 ยท Visual Memory Hooks

๐Ÿง  Primary vs secondary
โ€œPrimary = Platelet plug (Plug fast); Secondary = Solid fibrin (Slow)โ€.
๐Ÿง  Intact endothelium
โ€œPNHTTTโ€ โ€” Prostacyclin, Nitric oxide, Heparan sulfate, TFPI, Thrombomodulin, TPA*.
๐Ÿง  VWF storage
โ€œWeibel-Palade = Where VWF Parksโ€ (ECs); ฮฑ-granules in platelets.
๐Ÿง  Adhesion vs aggregation
โ€œIb = I bind the wall (VWF); IIb/IIIa = Two platelets hold hands (fibrinogen)โ€.
๐Ÿง  Receptor diseases
โ€œBernard-Soulier = no Ib; Glanzmann = no IIb/IIIa (Grab)โ€.
๐Ÿง  Dense granules
โ€œADP, ATP, Calcium, Serotonin โ€” small stuff in Denseโ€.
๐Ÿง  Aspirin
โ€œAspirin Acetylates COX forever โ€” life of the plateletโ€.
๐Ÿง  Factor nicknames
โ€œV Labile, VII Stable, VIII Antihemophilic, IX Christmas, X Stuart-Prower, XI PTA, XII Hagemanโ€.
๐Ÿง  Vitamin K factors
โ€œ1972โ€ โ€” II, VII, IX, X (+ C, S, Z).
๐Ÿง  Half-lives
โ€œVII is Short-lived (6 h) โ€” first to fall on warfarinโ€; II slowest (60 h) โ†’ 5 days.
๐Ÿง  Warfarin
โ€œWarfarin Wrecks the Epoxide reductaseโ€ โ†’ PIVKAs.
๐Ÿง  PT vs PTT
โ€œPeT the EXTRA (extrinsic) dog; PiTT is IN (intrinsic)โ€*.
๐Ÿง  Common pathway
โ€œ1, 2, 5, 10 โ€” common to bothโ€ (I, II, V, X).
๐Ÿง  Complexes
โ€œ7 + TF โ†’ 9 & 10; 9 + 8 โ†’ 10; 10 + 5 โ†’ 2โ€.
๐Ÿง  Contact factors
โ€œXII, Fletcher, Fitzgerald: long PTT, no bleedingโ€.
๐Ÿง  Thrombin’s jobs
โ€œFibrin, Five, Eight, Eleven, Thirteen, Platelets, Protein C, TAFIโ€.
๐Ÿง  Protein C
โ€œC and S Cut Five and Eightโ€.
๐Ÿง  Protein S
โ€œOnly the Free 40% is usefulโ€ โ€” 60% on C4bBP.
๐Ÿง  Heparin
โ€œLong heparin hugs thrombin; short heparin hits Xaโ€.
๐Ÿง  Fibrinolysis
โ€œTPA turns Plasminogen to Plasmin; PAI-1 Puts it off; ฮฑโ‚‚-antiplasmin Arrests free plasmin; TAFI Takes away lysinesโ€.
๐Ÿง  D-dimer
โ€œD-dimer = Done clotting AND Dissolving (cross-linked)โ€.

*Mnemonics are memory devices, not from Rodak.

Pattern Triggers

If you seeโ€ฆ Thinkโ€ฆ Becauseโ€ฆ
Pregnant woman with DVT; mother and brother with thrombosis Inherited deficiency of a coagulation inhibitor Rodak case study
Prolonged PT only Factor VII deficiency / early warfarin Extrinsic only
Prolonged PTT only, bleeding male Hemophilia A (VIII) or B (IX) X-linked intrinsic factors
Prolonged PTT, no bleeding XII, prekallikrein or HMWK deficiency Contact factors
PT and PTT both prolonged Common pathway (X, V, II, fibrinogen) or vitamin K/liver disease
Platelets don’t aggregate; GP IIb/IIIa normal Check fibrinogen (afibrinogenemia) Rodak Q3
No aggregation to any agonist except ristocetin* Glanzmann thrombasthenia GP IIb/IIIa absent
Aspirin intake, โ†“ thromboxane Bโ‚‚ COX-1 acetylated
Newborn with purpura fulminans Homozygous protein C deficiency
Normal PT/PTT, delayed bleeding, poor wound healing* Factor XIII deficiency Not detected by PT/PTT
High D-dimer Fibrin formed and lysed: DIC, DVT/PE
Normal D-dimer in low-risk patient Rules out VTE
Inflammation with thrombosis and low free protein S โ†‘ C4bBP binding Acute phase
Elevated TAT complex or F1.2 Active thrombin generation Markers

*Ristocetin response and XIII clinical signs are general knowledge; covered in platelet/coagulation disorder chapters.

Commonly Confused Pairs

Feature A B
Adhesion vs aggregation Reversible; VWFโ€“GP Ib/IX/V Irreversible; fibrinogenโ€“GP IIb/IIIa
ฮฑ-granules vs dense granules Large proteins (fibrinogen, VWF, V, PF4) Small molecules (ADP, ATP, Ca, serotonin)
Serine protease vs cofactor II, VII, IX, X, XI, XII, pre-K TF, V, VIII, HMWK
Factor V vs VII Labile, cofactor Stable, serine protease
Extrinsic vs intrinsic tenase TF:VIIa on TF cells; activates IX and X IXa:VIIIa on platelets; 50โ€“100ร— faster
PT vs PTT VII, X, V, II, I XII, pre-K, HMWK, XI, IX, VIII, X, V, II, I
Protein C vs protein S Serine protease (APC) Cofactor; 40% free
UFH vs LMWH Inactivates thrombin and Xa Mainly Xa
TPA vs PAI-1 Activates plasminogen Inhibits TPA
PAI-1 vs ฮฑโ‚‚-antiplasmin Blocks activation Blocks free plasmin
FDPs vs D-dimer From fibrinogen or fibrin Only cross-linked fibrin
Fibrin monomer vs polymer vs stabilized Fibrinopeptides removed Spontaneous Dโ€“E binding โ†’ XIIIa cross-links

Timeline Table

Event Timing Key Point Best Exam Use
Primary hemostasis Secondsโ€“minutes Short-lived Plug
Initiation phase Early 3โ€“5% of thrombin Cell-based model
Propagation After initiation โ‰ฅ95% thrombin Platelet surface
Fibrinolysis Hours after cross-linking Plasmin Clot removal
Factor VII after warfarin ~6 hours Shortest half-life Early INR rise
Full warfarin effect ~5 days Prothrombin half-life 60 h Overlap therapy*
Factor VIII in thawed plasma ~50% after 5 days Labile Blood bank
VIII replacement Every 12 hours Half-life 12 h Hemophilia
TAFI half-life 8โ€“10 minutes Short โ€”

*Heparin-warfarin overlap is general clinical knowledge.

4 ยท Diagnostic Flowcharts

Flowchart 1 โ€” Interpreting PT and PTT

PT prolonged, PTT normal โ†’ Factor VII (extrinsic) โ€” early warfarin, VII deficiency
PT normal, PTT prolonged โ†’ VIII, IX, XI (bleeding) or XII, pre-K, HMWK (no bleeding) โ€” or heparin*
Both prolonged โ†’ Common pathway: X, V, II, fibrinogen โ€” or vitamin K deficiency, liver disease, DIC*
Both normal with bleeding โ†’ Platelet/vascular disorder, VWD (mild), or factor XIII*
โš ๏ธ Common mistake: calling every prolonged PTT a bleeding risk โ€” contact factor deficiencies don’t bleed.

*Heparin, DIC, VWD and XIII interpretation beyond Rodak Ch. 37; detailed in coagulation-testing chapters.

Flowchart 2 โ€” The coagulation sequence (plasma-based)

Extrinsic start โ†’ TF + VIIa (+ Caยฒโบ, PL) โ†’ activates IX and X
Intrinsic start โ†’ XII + pre-K + HMWK โ†’ XIa โ†’ IXa; IXa + VIIIa โ†’ X
Common โ†’ Xa + Va โ†’ prothrombin โ†’ thrombin
Clot โ†’ Thrombin: fibrinogen โ†’ fibrin; XIII โ†’ XIIIa โ†’ cross-linked fibrin
โš ๏ธ Common mistake: forgetting that TF:VIIa also activates IX โ€” the pathways interlock.

Flowchart 3 โ€” Cell-based model

Injury exposes TF-bearing cells โ†’ TF:VIIa โ†’ small Xa, IXa
Xa:Va on TF cell โ†’ Trace thrombin
Trace thrombin โ†’ Activates platelets, V, VIII (from VWF), XI; starts fibrin
Activated platelet surface โ†’ IXa:VIIIa โ†’ Xa; Xa:Va โ†’ thrombin burst (โ‰ฅ95%)
Control โ†’ TFPI stops TF:VIIa; AT, APC/S, ZPI limit spread
โš ๏ธ Common mistake: thinking the extrinsic pathway makes most of the thrombin โ€” it only initiates.

Flowchart 4 โ€” Vitamin K cycle and warfarin

Glutamic acid on II, VII, IX, X, C, S, Z โ†’ ฮณ-carboxylase + vitamin K hydroquinone + Oโ‚‚/COโ‚‚
Product โ†’ Gla residues โ†’ bind Caยฒโบ โ†’ bind phosphatidylserine
Vitamin K epoxide โ†’ Recycled by epoxide reductase
Warfarin blocks epoxide reductase โ†’ PIVKAs (des-ฮณ-carboxyl) โ†’ no Caยฒโบ binding โ†’ inactive
Timing โ†’ VII drops in hours; prothrombin in 4โ€“5 days
โš ๏ธ Common mistake: saying vitamin K ‘activates’ factors โ€” it carboxylates them so they can bind calcium.

Flowchart 5 โ€” Natural anticoagulants

TF:VIIa + Xa formed โ†’ TFPI binds Xa, then TF:VIIa (protein S cofactor)
Thrombin binds thrombomodulin โ†’ Protein C โ†’ APC (EPCR helps)
APC + free protein S โ†’ Inactivate Va and VIIIa
Antithrombin (+ heparin) โ†’ Neutralizes thrombin, Xa, IXa, XIa, XIIa โ†’ TAT
ZPI + protein Z โ†’ Inhibits Xa (and XIa)
โš ๏ธ Common mistake: forgetting that only free protein S (40%) works as the APC cofactor.

Flowchart 6 โ€” Fibrinolysis and its brakes

Clot forms; plasminogen and TPA bind fibrin lysines โ†’ TPA โ†’ plasmin on fibrin
Plasmin digests fibrin โ†’ X, Y, D, E fragments; D-dimer from cross-linked fibrin
Brakes โ†’ PAI-1 (blocks TPA/UPA) ยท ฮฑโ‚‚-antiplasmin (free plasmin) ยท TAFI (removes lysines)
Drugs โ†’ Recombinant TPA (lysis) ยท tranexamic acid (anti-lysis)
โš ๏ธ Common mistake: calling D-dimer a marker of fibrinogenolysis โ€” it needs cross-linked fibrin.

5 ยท 25 High-Yield Facts

# Fact
1 Primary hemostasis is vasoconstriction plus the platelet plug; secondary hemostasis is fibrin formation by coagulation factors.
2 Intact endothelium secretes prostacyclin, nitric oxide, heparan sulfate, TFPI, thrombomodulin and TPA.
3 Endothelial cells synthesize and store VWF in Weibel-Palade bodies.
4 Tissue factor on subendothelial cells triggers coagulation by activating factor VII; it is not on normal ECs.
5 Platelet adhesion uses VWF binding GP Ib/IX/V; aggregation uses fibrinogen binding GP IIb/IIIa.
6 Fibrinogen is essential for platelet aggregation (afibrinogenemia and Glanzmann thrombasthenia impair it).
7 Dense granules contain ADP, ATP, calcium and serotonin; ฮฑ-granules contain fibrinogen, VWF, V, XI, protein S and PF4.
8 Aspirin permanently acetylates COX-1, blocking thromboxane Aโ‚‚ production.
9 Most coagulation factors are synthesized in the liver.
10 Factor XIII is a transglutaminase; the other enzymatic factors are serine proteases.
11 Tissue factor, V, VIII and HMWK are procoagulant cofactors.
12 Vitamin Kโ€“dependent proteins are II, VII, IX, X, protein C, protein S and protein Z.
13 Vitamin K ฮณ-carboxylates glutamic acid so factors can bind calcium and phospholipid.
14 Warfarin inhibits vitamin K epoxide reductase, producing nonfunctional PIVKAs.
15 Factor VII has the shortest half-life (6 h); full warfarin effect takes about 5 days.
16 Extrinsic tenase is TF:VIIa; intrinsic tenase is IXa:VIIIa; prothrombinase is Xa:Va.
17 The PT screens VII, X, V, II and fibrinogen; the PTT screens XII, pre-K, HMWK, XI, IX, VIII, X, V, II and fibrinogen.
18 Deficiencies of XII, prekallikrein and HMWK prolong the PTT but do not cause bleeding.
19 Factor VIII circulates bound to VWF; hemophilia A (VIII) and B (IX) are X-linked.
20 Thrombin cleaves fibrinopeptides A and B from fibrinogen to form fibrin monomer.
21 Factor XIIIa cross-links ฮณ chains of adjacent D domains to stabilize fibrin.
22 APC with protein S inactivates factors Va and VIIIa.
23 Antithrombin activity is accelerated about 2000-fold by heparin.
24 TPA secreted by endothelial cells converts plasminogen to plasmin; PAI-1 inhibits TPA.
25 D-dimer comes only from plasmin digestion of cross-linked fibrin and is used to rule out VTE.
โญ EXAM TIP โ€” The single most testable pattern

PT = VII + common (X, V, II, I); PTT = XII, pre-K, HMWK, XI, IX, VIII + common. Vitamin K: II, VII, IX, X, C, S, Z. Complexes: TF:VIIa โ†’ IX/X; IXa:VIIIa โ†’ X; Xa:Va โ†’ II. Regulators: APC + S cut Va/VIIIa; AT + heparin stop IIa/Xa; TFPI stops TF:VIIa. D-dimer = cross-linked fibrin lysis.

Quick Interpretation Table

Lab Finding Clinical Interpretation
Pregnant woman with DVT; mother with thrombophlebitis; brother with DVT after flight Inherited thrombophilia โ€” deficiency of an inhibitor (e.g., protein C, S, AT) (Rodak case study)*
Platelets fail to aggregate Assay fibrinogen (Rodak Q3)
PT 25 s, PTT normal, day 1 of warfarin Factor VII falling first
PTT 90 s, no bleeding history, before surgery Suspect factor XII/pre-K/HMWK deficiency
Stored plasma, low factor VIII activity VIII labile โ€” deteriorates in storage
Group O donor with low VWF Normal variant โ€” group O has lower VWF
Elevated D-dimer, low fibrinogen, low platelets Consistent with DIC
Elevated prothrombin fragment 1.2 and TAT Increased thrombin generation

*Case answers are my interpretation โ€” answer key not in the upload.

๐ŸŽด Flashcards โ€” Active Recall Practice

How it works: tap the card to flip it. Then mark it โœ“ Knew It or โœ— Review Again (buttons unlock after flipping). Use ๐Ÿ”€ Shuffle to randomize and ๐Ÿ Finish anytime โ€” your summary appears at the end, and you can drill only the cards you missed.

๐Ÿ“ Practice Quiz โ€” 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.

๐Ÿชค Trap Questions โ€” 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 ยท Rapid Revision Sheet

๐Ÿ“– READ THIS 2 HOURS BEFORE YOUR EXAM

Vascular Intima

  • Intact: PGIโ‚‚, NO, heparan sulfate, TFPI, TM, EPCR, TPA
  • Damaged: vasoconstriction, collagen, VWF, P-selectin, TF
  • VWF in Weibel-Palade bodies
  • TF not on normal ECs
  • PAI-1 and TAFI slow lysis

Platelets

  • Adhesion: VWFโ€“GP Ib/IX/V (Bernard-Soulier)
  • Aggregation: fibrinogenโ€“GP IIb/IIIa (Glanzmann)
  • Dense: ADP, ATP, Ca, serotonin
  • ฮฑ: fibrinogen, VWF, V, XI, PS, PF4, PDGF
  • Aspirin โ†’ COX-1 โ†’ no TXAโ‚‚ (TXBโ‚‚ โ†“)

Factor Names

  • I fibrinogen ยท II prothrombin ยท III TF ยท IV Ca
  • V labile ยท VII stable ยท VIII antihemophilic
  • IX Christmas ยท X Stuart-Prower ยท XI PTA
  • XII Hageman ยท pre-K Fletcher ยท HMWK Fitzgerald
  • XIII fibrin-stabilizing (transglutaminase)

Classes & Half-Lives

  • Serine proteases: II, VII, IX, X, XI, XII, pre-K
  • Cofactors: TF, V, VIII, HMWK
  • VII 6 h ยท VIII 12 h ยท II 60 h
  • Hemostatic level 25โ€“30%
  • Fibrinogen 200โ€“400 mg/dL

Vitamin K

  • II, VII, IX, X + C, S, Z
  • Glu โ†’ Gla (ฮณ-carboxylation) โ†’ Caยฒโบ binding
  • Warfarin โ†’ epoxide reductase โ†’ PIVKAs
  • Full effect ~5 days
  • Bacteroides fragilis, E. coli, greens

Complexes & Pathways

  • Extrinsic tenase TF:VIIa โ†’ IX, X
  • Intrinsic tenase IXa:VIIIa โ†’ X
  • Prothrombinase Xa:Va โ†’ II (+F1.2)
  • PT: VII, X, V, II, I
  • PTT: XII, pre-K, HMWK, XI, IX, VIII + common

Thrombin & Fibrin

  • Cleaves FPA/FPB โ†’ monomer โ†’ polymer
  • Activates V, VIII, XI, XIII, platelets
  • With TM: protein C and TAFI
  • XIIIa cross-links ฮณ chains (D domains)
  • Contact factors: long PTT, no bleeding

Cell-Based Model

  • Initiation on TF cells: 3โ€“5% thrombin
  • Trace thrombin activates platelets, V, VIII, XI
  • Propagation on COAT-platelets: โ‰ฅ95%
  • IXa:VIIIa 50โ€“100ร— faster
  • Clotting localized

Regulators

  • TFPI: Xa then TF:VIIa (protein S cofactor)
  • APC + free PS (40%) โ†’ Va, VIIIa
  • C4bBP binds 60% PS (acute phase)
  • AT + heparin (2000ร—) โ†’ IIa, Xa, IXa, XIa, XIIa
  • ZPI + protein Z โ†’ Xa

Fibrinolysis

  • TPA (ECs), UPA (kidney) โ†’ plasmin
  • Kringles bind fibrin lysine
  • PAI-1 ยท ฮฑโ‚‚-antiplasmin ยท TAFI
  • FDPs X, Y, D, E ยท D-dimer (cross-linked)
  • D-dimer: DIC, rule out VTE

9 ยท Final Memory Map

  • ๐Ÿฉธ NORMAL HEMOSTASIS
    • Primary Hemostasis
      • Vascular intima (anti- vs procoagulant)
      • Platelets: adhesion, aggregation, secretion, TXAโ‚‚
    • Coagulation Factors
      • Names, numbers, half-lives
      • Serine proteases ยท cofactors ยท transglutaminase
      • Vitamin K / warfarin
    • Pathways
      • Extrinsic ยท intrinsic ยท common (PT/PTT)
      • Complexes: tenases and prothrombinase
      • Cell-based: initiation โ†’ propagation
    • Thrombin & Fibrin
      • Six roles of thrombin
      • Fibrinogen โ†’ monomer โ†’ polymer โ†’ cross-linked
    • Regulation
      • TFPI ยท protein C/S ยท antithrombin/heparin ยท ZPI ยท serpins
    • Fibrinolysis
      • Plasminogen โ†’ plasmin (TPA, UPA)
      • PAI-1 ยท ฮฑโ‚‚-antiplasmin ยท TAFI
      • FDPs ยท D-dimer



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