Blood Work to Diagnose Clotting Factor Deficiency

Initial Screening Tests

The American Society of Hematology recommends starting with prothrombin time (PT) and activated partial thromboplastin time (APTT) as initial screening tests, followed by specific coagulation factor assays to identify which factor is deficient when either test is prolonged 1, 2
PT and APTT are the essential first-line tests that screen for clotting factor deficiencies, as recommended by the International Society on Thrombosis and Haemostasis 1, 2, 3, 4
A complete blood count (CBC) should be obtained simultaneously to assess platelet count and rule out thrombocytopenia as a cause of bleeding, according to the American Journal of Hematology 5
Fibrinogen level (Clauss method) is performed by 90% of specialists in first-line testing and helps identify consumptive coagulopathies, as reported by the Journal of Thrombosis and Haemostasis 4

Prolonged PT and/or APTT that corrects with a 50:50 mix with normal plasma indicates a factor deficiency rather than an inhibitor and necessitates specific factor assays, as stated by Blood Reviews 1, 2, 6
Both PT and APTT prolonged suggests common pathway deficiency (Factors II, V, X, fibrinogen) or combined deficiencies, according to Blood Reviews 1

Quantitative measurement of specific clotting factors through serial dilutions with factor-deficient plasma confirms the diagnosis, as recommended by Blood Reviews 1, 2, 6
If PT prolonged, measure Factors II, V, VII, and X, as suggested by the Journal of Thrombosis and Haemostasis 4
If APTT prolonged, measure Factors VIII, IX, XI, and XII, according to the Journal of Thrombosis and Haemostasis 4
If both prolonged, prioritize common pathway factors (II, V, X) and fibrinogen, as recommended by Blood Reviews 1

Factor activity levels below 20% reliably correlate with bleeding risk and are considered clinically significant, as reported by Blood Reviews 2, 7
Severe deficiency is typically defined as factor activity <10 IU/dL, moderate as 10-30 IU/dL, and mild as 30-50 IU/dL, according to Blood Reviews 2, 7
One-stage PT- or APTT-based clotting assays are sufficient for diagnosis of Factor X deficiency, as stated by Blood Reviews 1, 2
Measurement of factor X activity alone suffices to assess disease severity, according to Blood Reviews 1, 2

Von Willebrand factor testing (VWF antigen, VWF activity, Factor VIII) should be included if mucocutaneous bleeding is prominent, as recommended by the American Journal of Hematology 5, 8

Order PT, APTT, CBC, and fibrinogen as initial panel, as suggested by the Journal of Thrombosis and Haemostasis and the American Journal of Hematology 4, 5
If PT or APTT prolonged, perform 50:50 mixing study to differentiate deficiency from inhibitor, as recommended by Blood Reviews 1, 2
If mixing study corrects, order specific factor assays based on which screening test is abnormal, according to Blood Reviews and the Journal of Thrombosis and Haemostasis 1, 4
Confirm diagnosis with repeat testing showing factor activity consistently <50% (mild) or <10% (severe), as reported by Blood Reviews 2, 7