View source for 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

{| class="wikitable"
|+ Key Differentials by Lab Pattern
|-
! 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
|}


== When to Order What ==
* PT/INR: On all bleeding patients, before procedures, warfarin monitoring
* aPTT: If patient is on heparin or has unexplained bleeding
* D-dimer: Rule out [[Venous thromboembolism|VTE]] in low-pretest probability
* Fibrinogen/D-dimer: Suspect [[Disseminated intravascular coagulation|DIC]], trauma, [[Sepsis (main)|sepsis]]

==References==
<references/>

[[Category:Heme/Onc]]
[[Category:Labs]]