Further coagulation tests

(JAMA 2016;316:2146)

Mixing study

Mixing study

• useful if ↑ PT or PTT;
• mix Pt’s plasma 1:1 w/ normal plasma and retest
• PT/PTT normalizes → factor deficiency; then ✅ Coagulation factor levels
• PT/PTT remains elevated → factor inhibitor

Coagulation factor levels

• useful if mixing study suggests factor deficiency
• DIC → all factors consumed; ∴ ↓ factors V and VIII 🎱
• Liver disease → ↓ all factors except VIII; ∴ ↓ factor V, normal factor VIII
• Vitamin K deficiency → ↓ factors II, VII, IX, X (and protein C, S); ∴ normal V and VIII

DIC screen

• ↓ fibrinogen (consumed)
• fibrin degradation products (FDPs, ⊕ from intense fibrinolysis),
• ↑ D-dimer (more specific FDP test that detects degradation of X-linked fibrin)