Medicines that increase the risk of bleeding should obviously not be given to those with hemophilia. These include anticoagulants, aspirin, and nonsteroidal anti-inflammatory drugs (NSAIDs). The laboratory should not routinely encounter interference from these types of drugs since patients are advised not to take them. However, there is a medication used to treat hemophilia A called emicizumab (Hemlibra) that is worth noting. This therapy uses a monoclonal antibody that binds to factors IXa and X. By binding them, it brings them into proximity to each other. This 'scaffold' allows factor IXa to activate factor X. This activation is the role that factor VIII normally plays.
Emicizumab was approved by the Food and Drug Administration (FDA) for patients with hemophilia A in 2018. Emicizumab is not effective for acute bleeding episodes but is used as a prophylactic measure in a chronic dosing fashion. Importantly, the laboratory should be aware that the usual aPTT test and factor VIII activity assays will be affected by emicizumab. Thus, these assays can't be used to monitor the patient. If a patient on emicizumab prophylaxis requires a factor VIII infusion, the factor VIII activity must be measured using a chromogenic assay for factor VIII rather than an assay that measures factor VIII activity.
