Coagulation studies
Core Labs
PT (Prothrombin Time)
- Measures extrinsic & common pathways (factors I, II, V, VII, X)
- Normal: 11–13.5 sec
- Prolonged in: warfarin use, liver disease, vitamin K deficiency, DIC
INR (International Normalized Ratio)
- Standardized PT
- Normal: 0.8–1.2
- Target therapeutic: 2–3 (DVT/PE/AF); 2.5–3.5 (mechanical valves)
- >1.5 with bleeding or planned procedure may warrant reversal
aPTT (Activated Partial Thromboplastin Time)
- Measures intrinsic & common pathways (factors I, II, V, VIII, IX, X, XI, XII)
- Normal: 25–35 sec
- Prolonged in: heparin, hemophilia A/B, lupus anticoagulant, DIC
Fibrinogen
- Acute phase reactant; substrate for clot formation
- Normal: 200–400 mg/dL
- Low in: DIC, liver disease, fibrinolysis
D-Dimer
- Marker of fibrin degradation
- Normal: <500 ng/mL (varies by assay/age)
- Elevated in: VTE, trauma, infection, cancer, pregnancy, DIC
Red Flags in the ED
- Bleeding with elevated PT/INR only: Think warfarin, liver disease, vitamin K deficiency.
- Bleeding with elevated aPTT only: Think heparin, hemophilia, lupus anticoagulant.
- Both PT and aPTT elevated: Consider DIC, liver failure, anticoagulant overdose.
- Normal PT/aPTT with bleeding: Platelet dysfunction, von Willebrand disease, factor XIII deficiency.
- Elevated D-dimer: Not specific — never diagnostic, but sensitive for VTE when combined with low Wells score.
Urgent Reversals
Warfarin (INR ≥3 or bleeding)
- Vitamin K IV + PCC (e.g., Kcentra)
- FFP if PCC unavailable
Heparin
- Protamine sulfate (1 mg per 100 units heparin given in last 2–3 hrs)
DOACs (apixaban, rivaroxaban)
- Consider andexanet alfa (if available)
- Activated charcoal if <2 hrs from ingestion
- PCC off-label if bleeding and drug unknown
| PT | aPTT | Diagnosis |
|---|---|---|
| ↑ | Normal | Warfarin, early liver disease |
| Normal | ↑ | Heparin, hemophilia, lupus inhibitor |
| ↑ | ↑ | DIC, advanced liver disease, vitamin K deficiency |
| Normal | Normal | Platelet disorder, von Willebrand disease |