View source for Coagulation Studies

==Background==
*Coagulation studies assess the function of the coagulation cascade and guide management of bleeding, anticoagulation, and coagulopathy in the ED<ref name="statpearls">Rountree KM, Lopez PP. Partial Thromboplastin Time. In: ''StatPearls''. Treasure Island (FL): StatPearls Publishing; 2025. PMID 30252830.</ref>
*Standard panel includes: '''PT''' (prothrombin time), '''INR''' (international normalized ratio), and '''PTT/aPTT''' (activated partial thromboplastin time)
*Additional coagulation-related tests include: '''fibrinogen''', '''D-dimer''', '''thrombin time (TT)''', '''mixing studies''', and '''anti-factor Xa levels'''
*Collected in a '''citrate (blue top) tube''' — tube must be filled to the line; underfilling causes falsely prolonged results due to excess citrate
*Evidence suggests coagulation panels are frequently over-ordered in the ED with limited impact on management in many clinical scenarios<ref name="long">Long B, Liang SY, Koyfman A. Emergency medicine misconceptions: utility of routine coagulation panels in the emergency department setting. ''Am J Emerg Med''. 2021;41:149-153. PMID 32067862.</ref>

==Components==
===PT / INR===
*Assesses: Extrinsic and common pathways (Factors VII, X, V, II, fibrinogen)
*Normal PT: ~11–13.5 seconds (lab-dependent)
*Normal INR: 0.8–1.2
*Primary uses:
**Monitor [[Warfarin|warfarin]] therapy (target INR 2.0–3.0 for most indications; 2.5–3.5 for mechanical valves)
**Assess liver synthetic function (component of MELD score)
**Screen for [[Disseminated Intravascular Coagulation|DIC]], vitamin K deficiency
**Pre-thrombolytic assessment
*Causes of prolonged PT/INR:
**Warfarin use
**Vitamin K deficiency (malnutrition, prolonged antibiotics, cholestasis)
**Liver disease/hepatic failure
**[[DIC]]
**Factor VII deficiency (isolated PT prolongation with normal PTT)
**Supratherapeutic anticoagulation

===PTT / aPTT===
*Assesses: Intrinsic and common pathways (Factors XII, XI, IX, VIII, X, V, II, fibrinogen)
*Normal aPTT: ~25–35 seconds (lab-dependent)
*Primary uses:
**Monitor unfractionated heparin (UFH) therapy
**Screen for hemophilia (Factor VIII or IX deficiency)
**Evaluate unexplained bleeding
**Detect lupus anticoagulant (paradoxically causes thrombosis, not bleeding)
*Causes of prolonged PTT:
**Heparin use (most common in ED)
**Hemophilia A (Factor VIII deficiency) or B (Factor IX deficiency)
**[[Von Willebrand Disease]]
**DIC
**Direct thrombin inhibitors (dabigatran, argatroban, bivalirudin)
**Lupus anticoagulant
**Severe liver disease

===Fibrinogen===
*Normal: 200–400 mg/dL
*Critical value: < 100 mg/dL (high bleeding risk)
*Acute phase reactant — may be falsely normal or elevated in early DIC or inflammatory states
*Decreased in: DIC (consumptive), massive transfusion (dilutional), severe liver disease, dysfibrinogenemia, thrombolytic therapy
*Key component of DIC screening panel
*Target > 150–200 mg/dL in active hemorrhage and obstetric emergencies<ref name="adelborg">Adelborg K, Larsen JB, Hvas AM. Disseminated intravascular coagulation: epidemiology, biomarkers, and management. ''Br J Haematol''. 2021;192(5):803-818. PMID 33555612.</ref>

===D-Dimer===
*Fibrin degradation product; marker of fibrinolysis
*Normal: < 500 ng/mL (age-adjusted cutoff: age × 10 ng/mL for patients > 50 years)
*Primary ED uses:
**Rule out [[Pulmonary Embolism|PE]] and [[Deep Vein Thrombosis|DVT]] (high sensitivity, low specificity; useful only with low-to-moderate pretest probability)
**Component of DIC diagnostic scoring (ISTH criteria)
*Elevated in: VTE, DIC, sepsis, trauma, surgery, pregnancy, malignancy, inflammation, post-thrombolysis — very nonspecific

===Thrombin Time (TT)===
*Measures conversion of fibrinogen to fibrin (final common step)
*Normal: ~14–19 seconds
*Prolonged by: heparin, direct thrombin inhibitors (dabigatran), hypofibrinogenemia (< 100 mg/dL), dysfibrinogenemia, elevated fibrin degradation products
*Useful for detecting heparin contamination of specimens and confirming dabigatran effect

===Anti-Factor Xa Level===
*Uses:
**Monitor LMWH (enoxaparin) — therapeutic range 0.5–1.0 IU/mL (treatment dose); 0.2–0.5 IU/mL (prophylactic)
**Monitor UFH (increasingly used as alternative to aPTT)
**Some assays can estimate DOAC (rivaroxaban, apixaban) drug levels, but availability is limited
*Draw 4 hours post-dose for LMWH (peak level)

==Interpretation Patterns==
{| class="wikitable"
|-
! PT/INR !! PTT !! Fibrinogen !! D-Dimer !! Likely Diagnosis
|-
| ↑ || Normal || Normal || Normal || Warfarin, vitamin K deficiency, early liver disease, Factor VII deficiency
|-
| Normal || ↑ || Normal || Normal || Heparin, hemophilia A/B, vWD, lupus anticoagulant, Factor XI/XII deficiency
|-
| ↑ || ↑ || Normal || Normal || Common pathway defect (Factor X, V, II), liver disease, supratherapeutic anticoagulation, direct thrombin inhibitor
|-
| ↑ || ↑ || ↓ || ↑↑ || '''[[DIC]]''' (consumptive coagulopathy)
|-
| ↑ || ↑ || ↓ || Normal/↑ || Severe liver failure, massive transfusion (dilutional coagulopathy)
|-
| Normal || Normal || Normal || ↑ || VTE, inflammation, infection, malignancy, post-surgical (D-dimer alone is nonspecific)
|}

==Evaluation==
===Appropriate ED Indications===
*Active hemorrhage or hemodynamic instability from suspected bleeding
*Patients on anticoagulants (warfarin, heparin, DOACs) presenting with bleeding, trauma, or requiring urgent procedures
*Suspected [[DIC]] (order PT, PTT, fibrinogen, D-dimer, platelets)
*Severe [[Sepsis|sepsis]]/septic shock
*Liver failure or suspected hepatic coagulopathy
*Pre-thrombolytic assessment ([[Stroke|stroke]], [[STEMI]], massive PE)
*Unexplained petechiae, purpura, or mucosal bleeding
*Massive transfusion protocol activation

===Low-Yield Indications (Consider NOT Ordering)===<ref name="long"/>
*Routine preoperative screening in patients without bleeding history
*Chest pain / ACS workup without planned anticoagulation or thrombolysis
*Simple laceration repair
*Before initiating anticoagulation in patients with no clinical bleeding
*Routine admission screening in well-appearing patients

==Management==
===Warfarin Reversal (Elevated INR)===
*INR 4.5–10, no bleeding: Hold warfarin; consider oral vitamin K 1–2.5 mg
*INR > 10, no bleeding: Hold warfarin; oral vitamin K 2.5–5 mg
*'''Serious/life-threatening bleeding (any INR):''' IV vitamin K 10 mg PLUS 4-factor PCC (Kcentra; dose based on INR and weight) — do not wait for vitamin K effect; PCC works within minutes<ref name="tomaselli">Tomaselli GF, Mahaffey KW, Cuker A, et al. 2020 ACC expert consensus decision pathway on management of bleeding in patients on oral anticoagulants. ''J Am Coll Cardiol''. 2020;76(5):594-622. PMID 32680646.</ref>
*FFP (15–20 mL/kg) is second-line if PCC is unavailable — slower onset, larger volume

===Heparin Reversal===
*UFH: Protamine sulfate (1 mg per 100 units of heparin given in last 2–3 hours; max 50 mg)
*LMWH: Protamine partially reverses (~60%); 1 mg per 1 mg enoxaparin given in last 8 hours

===DOAC Reversal===
*Dabigatran: Idarucizumab (Praxbind) 5 g IV — specific reversal agent
*Rivaroxaban/Apixaban: Andexanet alfa (Andexxa) if available; otherwise 4-factor PCC (50 units/kg) as an off-label alternative<ref name="tomaselli"/>
*Activated charcoal if ingestion within 2 hours

===DIC Management===
*Treat underlying cause (sepsis, malignancy, obstetric emergency)
*Transfuse as indicated: platelets (if < 10,000 or < 50,000 with bleeding), cryoprecipitate (if fibrinogen < 100–150 mg/dL), FFP (if PT/PTT significantly prolonged with bleeding)
*Do NOT give heparin empirically — consider only in DIC with predominant thrombotic phenotype in consultation with hematology

==Disposition==
*Coagulopathy with active bleeding requires admission, often to ICU
*Supratherapeutic INR without bleeding may be managed with dose adjustment and close follow-up if patient is reliable
*New unexplained coagulopathy warrants admission for workup
*Patients on anticoagulants after trauma (especially head trauma) may require prolonged observation and repeat imaging regardless of initial coagulation results

==See Also==
*[[CBC]]
*[[DIC]]
*[[Warfarin]]
*[[Heparin]]
*[[Pulmonary Embolism]]
*[[DVT]]
*[[Hemophilia]]
*[[Von Willebrand disease]]
*[[Massive Transfusion]]
*[[Peripheral blood smear]]
*[[Liver failure]]

==External Links==
*[https://www.ncbi.nlm.nih.gov/books/NBK604215/ Interpretation of Blood Clotting Studies and Values - StatPearls]
*[https://emcrit.org/ibcc/coag/ Coagulation Tests - EMCrit IBCC]
*[https://pubmed.ncbi.nlm.nih.gov/32067862/ Emergency medicine misconceptions: utility of routine coagulation panels - Am J Emerg Med 2021]
*[https://pubmed.ncbi.nlm.nih.gov/32680646/ 2020 ACC Expert Consensus on Management of Bleeding on Oral Anticoagulants - JACC 2020]

==References==
<references/>

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