Which laboratory test is crucial for confirming a diagnosis of hemophilia?

The Factor VIII/IX assay is essential for confirming a diagnosis of hemophilia because hemophilia is a disorder characterized by deficiencies in specific clotting factors—either Factor VIII, which leads to hemophilia A, or Factor IX, which is associated with hemophilia B. Measuring the levels of these factors directly assesses the specific deficiency responsible for the bleeding disorder.

In contrast, a platelet count assesses the number of platelets in the blood, which is not directly related to hemophilia, as hemophilia is primarily a problem with clotting factors rather than the quantity of platelets. The Basic Metabolic Panel measures various chemical components in the blood, including glucose, calcium, and electrolytes, but does not evaluate coagulation factors. The Erythrocyte Sedimentation Rate tests for inflammation in the body and is unrelated to hemostatic function and the diagnosis of bleeding disorders. Therefore, the Factor VIII/IX assay is the critical test in this context, providing the precise information needed to diagnose hemophilia.