Coagulation

Factors II, V, VIII, HMWK -> cofactors

Factors II, VII, 9-12, Prekallikrein -> serine proteases

Vitamin K Dependent Factors

• Serine Proteases
  • Factors II, VII, IX, X
  • Regulatory control proteins C, S, Z

Factor	Other Names	Pathway(s)	Role	Location of Synthesis
I	Fibrinogen	Common
II	Prothrombin	Common
III	Tissue Factor (TF)
IV	Ca2+
V	Labile factor	Common
VII	Stable factor	Extrinsic
VIII	Anti-hemophilic factor	Intrinsic
IX	Christmas Factor	Intrinsic
X	Stuart-Prower Factor	Common
XI	PTA (Plasma Thromboplastin Antecedent)	Intrinsic
XII	Hageman Factor	Intrinsic
XIII	Fibrin Stabilizing Factor (FSF)		Crosslinks adjacent fibrin strand D-domains to make an insoluble polymer
VWF
HMWK	High Molecular Weight

Stages of Hemostasis

1. Primary hemostasis
2. Secondary hemostasis
3. Fibrin clot formation
4. Coagulation inhibition

Protein Z

• Z-dependent protease inhibitor (ZPI)
• Protein Z enhances ZPI activity
  • inhibits factor X and XI

Restoring Blood Flow

• Fibrinolytic proteins
  • Plasminogen
    • Converted into plasmin by TPA and UPA
    • Plasmin helps restore blood flow
  • TPA
  • UPA

1.85*10^-3 x (100-HCT) x v

300ul citrate

Coagulation Testing

All coagulation testing uses sodium citrate (light blue top) tubes to yield plasma. Centrifuge to separate plasma from platelets, yielding platelet poor plasma (to prevent activation of coagulation).

• RT: 4 hours
• Frozen: 2 weeks (-20C) to 6 months (-80C)

What? (Test)	Why?	How? (Methodology)	Associated Conditions	RI
PT/INR (Prothrombin Time)	Assess deficiencies or inhibitors of extrinsic or common pathways	Calcium thromboplastin added to sample (calcium and tissue factor source) Activates coagulation cascade Measured optically or mechanically Optical: light scattered as fibrin strands form Mechanical: magnetic balls oscillates, movement impeded by clot		11.5 - 13.5 s INR: 0.9 - 1.2
APTT	Assess deficiencies or inhibitors of intrinsic or common pathways	APTT reagent added to sample (contains contact activator and phospholipids) Activation of factor XII and XI Calcium then added to activate factor IX and VIII Factor X activated, causing cascade to activate Factor II and I, forming fibrin clot		23 - 35 s
Fibrinogen (Clauss Assay)	Assess fibrinogen activity	Clauss assay uses reference plasma samples with known concentrations of fibrinogen Run thrombin time (high thrombin concentration) and plot results of concentration vs. time Patient samples can then be run and compared to the curve to determine fibrinogen concentration Clot time inversely proportional to fibrinogen activity	Loss or consumption of fibrinogen Bleeding Hyperfibrinolysis DIC Decreased production Liver disease Congenital hypofibrinogenemia Dysfibrinogenemia	1.5 - 4 g/L
Thrombin Time	Assess deficiencies of fibrinogen or the presence of thrombin inhibitors	Low concentration of thrombin added to cleave fibrinogen → fibrin Measure time to form fibrin clot	Drugs Heparin Direct thrombin inhibitors (dabigatran, apixaban, etc.) Conditions Congenital fibrinogen deficiencies Acquired fibrinogen deficiencies Increased clot breakdown (e.g., DIC)	12 - 16 s
D-Dimer	Assess presence of fibrinolysis activation	Various methods (ELISA, latex immunoassay, etc.) Latex immunoassays: latex beads bind to D-Dimers and decrease measured absorbance	Negative results highly sensitive and specific for ruling out venous thromboembolism (VTE) in certain populations Positive results non-specific DIC Various diseases and infections Inflammation Recent surgery/trauma Cancer Elderly people Pregnancy (especially later trimesters)	< 600 ug/L FEU*
Unfractionated Heparin/Anti-Xa Assay	Assess anticoagulant activity	Known value of Factor Xa is added in excess to patient sample Complex formed between drug and coagulation factor Unbound FXa hydrolyzed and abosrbance measured Result converted to a drug concentration	Drugs Unfractionated heparin Low molecular weight heparin Fondaparinux Direct FXa inhibitors Rivaroxaban Apixaban Edoxaban	Varies by drug
Factor Assays

'* FEU or DEU may be used for measurement

Anticoagulant Drugs

Drug	Mechanism of Action	Monitoring	Reversal
Unfractionated Heparin (UFH)	INDIRECT Various length chains of glycosaminoglycans Combines with antithrombin (as pentasaccharide) Inhibits IIa, Xa, IXa, XIa, and XIIa	APTT Anti-Xa assay	Elective Discontinue IV for 4 hoursEmergency Protamine sulfate
Low Molecular Weight Heparin (LMWH) Dalteparin, enoxaparin, nadroparin, tinzaparin, etc.	INDIRECT Smaller chains of heparin (fractionated out) Combine with antithrombin (pentasaccharide) Inhibits Xa and IIa only Relative inhibition of factors (Xa:IIa ratio) various by formulation	Not usually required Anti-Xa assay only	Elective 12-24 hours discontinuation Emergency Andexanet alpha pending approval Protamine may reverse effects on IIa only for intravascular LMWH
Warfarin (Coumadin)	Vitamin K antagonist Prevents activation of vitamin K-dependent factors II, VII, IX, X, anticoagulant proteins	PT/INR	Elective 5 days discontinuation (bridging may be done for some patients) Vitamin K if non-urgent Emergency Vitamin K - activates factors already present Prothrombin complex concentrates (PCCs - Octaplex) Contain Vitamin K-dependent factors and some heparin Contraindicated in HIT
Fondaparinux	INDIRECT Synthetic pentasaccharide Combines with antithrombin Inhibits FXa only	Not usually required Anti-Xa assay only	Elective 1-2 days discontinuation Emergency Andexanet alpha (pending approval) may be helpful Otherwise, none
Direct Thrombin Inhibitors (DTIs) Dabigatran (VTE, stroke prevention) Argatroban, Bivalirudin, Lepirudin (HIT treatment)	DIRECT Synthetic Directly inhibit thrombin, do not require antithrombin (direct-acting)	Not usually required	Elective varies Emergency (dabigatran) Idarucizumab Activated charcoal (within 2 hours) Hydration
Direct Xa Inhibitors Rivaroxaban Apixaban Edoxaban	Synthetic Directly inhibit FXa (don't require antithrombin) Used for prevention of VTE and stroke	Not usually required Anti-Xa assay only	Elective varies Emergency Andexanet alpha (pending approval) Prothrombin complex concentrates (PCCs - Octaplex)