What tests are used to diagnose Hemophilia (coagulation disorder)?

From the Guidelines

Testing for hemophilia should involve a combination of a complete blood count (CBC), coagulation studies like activated partial thromboplastin time (aPTT) and prothrombin time (PT), and specific factor assays to measure levels of clotting factors VIII and IX, as recommended by the most recent guidelines 1. The primary tests for diagnosing hemophilia include:

• A complete blood count (CBC) to assess platelet number, fibrinogen, PT, PTT, and international normalized ratio, as suggested in the diagnostic work-up for acquired hemophilia A 2
• Coagulation studies like activated partial thromboplastin time (aPTT) and prothrombin time (PT) to evaluate the intrinsic and extrinsic coagulation pathways
• Specific factor assays to measure levels of clotting factors VIII and IX, which can be performed using either the one-stage clotting assay (OSCA) or the chromogenic assay (CHR) 3 For suspected hemophilia A, factor VIII activity is measured, while factor IX activity is assessed for hemophilia B. These tests typically require a blood sample drawn from a vein. Genetic testing may also be performed to identify specific mutations and can be useful for family planning or confirming diagnosis in unclear cases. Testing is recommended for individuals with unexplained bleeding episodes, family history of hemophilia, or abnormal bleeding after surgery or injury. In newborns with a family history, cord blood can be tested at birth. The severity of hemophilia is determined by the percentage of normal clotting factor activity: severe (<1%), moderate (1-5%), or mild (5-40%) 1. Early diagnosis is crucial for proper management and prevention of complications like joint damage from internal bleeding. It is essential to ensure that the necessary laboratory tests are readily available for clinicians to order, and that laboratories develop a nomenclature to define which factor assay is actually performed, as suggested in the practical solutions for laboratory assay measurement of modified clotting factor concentrates 4.

From the Research

Diagnosis of Haemophilia

• Haemophilia A and B are hereditary coagulation disorders caused by functional and quantitative abnormalities of coagulation factor VIII (FVIII) in haemophilia A and coagulation factor IX (FIX) in haemophilia B 5.
• A definitive diagnosis is made through the measurement of FVIII or FIX activity and ruling out other pathological conditions or diseases with decreased FVIII or FIX activity 5.
• The most frequently used assays are based on activated partial thromboplastin time, using a one-stage or two-stage process 6.

Laboratory Testing for Haemophilia

• Definitive diagnosis of haemophilia and treatment monitoring is reliant on demonstrating factor VIII (FVIII; hemophilia A) or factor IX (FIX; hemophilia B) deficiency using a functional coagulation assay 6.
• The one-stage activated partial thromboplastin time (aPTT)-based clotting assay is the most commonly used method worldwide for testing FVIII or FIX activities 7.
• Variation between one-stage FVIII or FIX activities has been reported in the measurement of some standard and extended half-life factor replacement therapies and gene therapy for hemophilia B using different aPTT reagents 7.

Challenges in Laboratory Testing

• Increasing use of extended half-life (EHL) recombinant clotting factors and innovative non-factor replacement therapeutics poses challenges to clinicians and coagulation laboratories due to the lack of standardized assays for monitoring of hemostatic parameters 6.
• The choice of reagent or methodology can strongly influence the resulting activity, and discrepancy between one-stage and chromogenic reagents has been demonstrated in some patients with mild hemophilia A or B 7.

Treatment and Management

• The treatment for hemophilia is mainly replacement therapy using clotting factor concentrates (standard or extended half-life), such as prophylaxis or on-demand therapy for bleeding 5.
• Recent advances in haemophilia therapy have worked to eliminate challenges associated with traditional treatments, including half-life extension of factor concentrates and subcutaneous administration of therapeutics 8.