Analytical coagulation assays are essential for the diagnosis, classification, and management of Hemophilia A and B. Initial screening often begins with aPTT, which is typically prolonged due to the disruption of the intrinsic coagulation pathway. Confirmatory testing relies on FVIII or FIX activity assays, which quantify the specific factor levels and determine disease severity. In complex cases or when patients are receiving non-factor therapies, chromogenic assays offer more accurate, interference-resistant measurement. Global assays such as Thrombin Generation Assays (TGA) and Thromboelastography (TEG) provide functional insight into thrombin production and clot quality, helping assess bleeding risk or treatment efficacy. Additional assays like PT, fibrinogen, and D-dimer support differential diagnosis or monitor complications, while dTT may assist in identifying coexisting anticoagulant effects. Together, these tools offer a comprehensive analytical framework for optimizing care in patients with Hemophilia A and B.

Analytical PK Assays

What They Measure: These assays quantify the plasma levels of recombinant Factor VIII (for Hemophilia A) or Factor IX (for Hemophilia B) over time.

Related to Hemophilia A/B: y determining parameters such as peak concentration, half-life, and clearance, clinicians can tailor dosing schedules to maintain optimal factor levels and minimize bleeding episodes.

Immunogenicity Assays

What it measures: These assays detect the presence of inhibitors—anti-factor antibodies—that may develop in response to replacement therapy.

Related to Hemophilia A/B: Early detection of inhibitors is critical, as these antibodies can neutralize the therapeutic protein, reducing efficacy and necessitating alternative treatment strategies.

Activated Partial Thromboplastin Time (aPTT)

What it measures: The time it takes for plasma to clot via the intrinsic and common coagulation pathways, assessing factors XII, XI, IX, VIII, X, V, II, and fibrinogen.

Related to Hemophilia A/B: aPTT is typically prolonged in both Hemophilia A (FVIII deficiency) and Hemophilia B (FIX deficiency), making it a key screening tool. However, it is not specific, so factor activity assays are needed for confirmation.

Thrombin Generation Assay (TGA)

What it measures: The rate and amount of thrombin formed over time in plasma after triggering coagulation. Provides a global assessment of coagulation potential.

Related to Hemophilia A/B: TGA is sensitive to reductions in thrombin generation seen in FVIII or FIX deficiencies. It’s useful for assessing overall functional impact, bleeding risk, and therapeutic response—especially when standard assays show borderline results.

Thromboelastography (TEG®)

What it measures: The viscoelastic properties of whole blood during clot initiation, formation, strength, and lysis.

Related to Hemophilia A/B: TEG may show delayed clotting and reduced clot strength in moderate to severe FVIII or FIX deficiencies. It offers a global picture of clot dynamics and is valuable in guiding treatment decisions during surgery or acute bleeds.

D-dimer Assay

What it measures: The viscoelastic properties of whole blood clot formation over time, iWhat it measures: Fibrin degradation products, indicating ongoing fibrinolysis and clot breakdown.

Related to Hemophilia A/B: D-dimer is not typically elevated in untreated hemophilia but may rise during bleeding episodes or in the context of complications like thrombosis or inflammation. It’s more relevant for excluding thrombotic disorders in hemophilia patients receiving certain therapies.

Fibrinogen Assay

What it measures: The concentration of functional fibrinogen, the final substrate converted to fibrin during clot formation.

Related to Hemophilia A/B: Fibrinogen levels are usually normal in Hemophilia A and B. However, fibrinogen may be monitored in bleeding episodes or during replacement therapy to assess overall clot-forming capacity.

Prothrombin Time (PT)

What it measures: The time required for plasma to clot via the extrinsic and common pathways, primarily reflecting Factor VII and the common pathway (X, V, II, fibrinogen).

Related to Hemophilia A/B: PT is typically normal in both Hemophilia A and B since these disorders affect the intrinsic pathway. It helps distinguish hemophilia from vitamin K deficiencies or liver disease when used alongside aPTT.

Dilute Thrombin Time (dTT)

What it measures: The conversion of fibrinogen to fibrin in the presence of low concentrations of thrombin. Often used to detect direct thrombin inhibitors.

Related to Hemophilia A/B: Not commonly used for diagnosis, but may be relevant in differential diagnosis when other anticoagulants or inhibitors are suspected. Can help rule out non-factor-related causes of abnormal clotting results.

FVIII Activity Assay

What it measures: The functional activity of Factor VIII in plasma, using either one-stage clot-based or chromogenic methods.

Related to Hemophilia A: This is the definitive test for diagnosing Hemophilia A and determining its severity. It’s also essential for monitoring replacement therapy and detecting inhibitors.

FIX Activity Assay

What it measures: The functional activity of Factor IX in plasma, performed using one-stage clot-based or chromogenic assays.

Related to Hemophilia B: The confirmatory diagnostic test for Hemophilia B. Used to classify severity, guide treatment, and monitor response to FIX replacement or gene therapy.