Causes of Abnormal PT and/or aPTT
Prolonged Prothrombin Time (PT)
1. Acquired deficiency of FVII
a. Early warfarin therapy
b. Early vitamin K deficiency
c. Early liver disease
2. Drugs
a. Direct Xa inhibitors - Rivaroxaban, apixaban, edoxaban (typically prolong aPTT)
3. Congenital deficiency of FVII
4. Specific inhibitors to FVII (exceptionally rare)
Prolonged Activated Partial Thromboplastin Time (aPTT)
1. Therapeutic unfractionated heparin - Other anticoagulants may prolong the aPTT alone but typically prolong PT too
2. Nonspecific inhibitors e.g. antiphospholipid antibodies
3. Congenital intrinsic coagulation factors deficiencies: Contact pathway factors (prekallikrein, kallikrein, HMWK), FXII, FXI, FIX, FVIII
4. Specific inhibitors to one factor e.g. FVIII antibody
Prolonged PT and aPTT
1. Pre-analytical cause
e.g. heparin contamination, under filling of tube
2. Drugs
a. Direct or indirect inhibitory drugs e.g. direct thrombin inhibitors, heparin
b. Supratherapeutic warfarin effect - FII, FVII, FIX, FX < 30%
3. Inhibitors
a. Nonspecific inhibitor e.g. antiphospholipid antibodies
b. Specific inhibitors to the common pathways (rare)
4. Decreased factor synthesis
a. Congenital deficiency
b. Reduced liver synthesis - Impaired production Fll, FV, FVII, FIX, FX, FXI, FXII, FXIII, dysfibrinogenemia
c. Severe vitamin K deficiency ( decreased Fll, FVII, FIX, FX).
5. Factor consumption or binding
a. Massive hemorrhage
b. Disseminated intravascular coagulation (DIC)
c. Factor X deficiency associated with systemic amyloidosis
- Jorge Cortés @Jcortesizaguirr
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