APTT-based activated protein C resistance test

APTT-based activated protein C resistance test is a diagnostic examination used to assess the resistance of blood plasma to activated protein C (APC), which is a critical factor in the regulation of blood coagulation. This test is primarily used to detect the presence of Factor V Leiden mutation, a genetic alteration associated with an increased risk of venous thrombosis. The APTT-based activated protein C resistance test is an important tool in the field of hematology and thrombosis research and management.

Overview

Activated protein C resistance (APCR) is a condition wherein the anticoagulant response to activated protein C is reduced. This resistance can lead to an increased risk of developing venous thromboembolism (VTE), including conditions such as deep vein thrombosis (DVT) and pulmonary embolism (PE). The most common cause of APCR is the Factor V Leiden mutation, which results from a single point mutation (G1691A) in the gene for Factor V, making it resistant to inactivation by APC.

Test Procedure

The APTT-based activated protein C resistance test involves adding activated protein C to a patient's plasma and then measuring the Activated Partial Thromboplastin Time (APTT). The APTT is a screening test that evaluates the intrinsic and common pathways of the coagulation cascade. In individuals with normal response to APC, the addition of APC prolongs the APTT, indicating a proper anticoagulant response. However, in individuals with APC resistance, the prolongation of APTT is significantly less, indicating an abnormal response.

Interpretation of Results

The ratio of the APTT in the presence of APC to the APTT in the absence of APC is calculated to determine the level of resistance. A lower ratio indicates a higher degree of resistance to activated protein C and a higher risk of thrombosis. It is important to note that the interpretation of results may vary depending on the specific reagents and protocols used in the laboratory.

Clinical Significance

The APTT-based activated protein C resistance test is crucial for the diagnosis of APC resistance and the identification of individuals at increased risk for venous thromboembolism. It is particularly important for patients with a personal or family history of VTE, as it can guide the need for preventive measures or long-term anticoagulation therapy. Additionally, the test is used in the investigation of unexplained miscarriage, as APC resistance has been associated with adverse pregnancy outcomes.

Limitations

While the APTT-based test is useful for detecting APC resistance, it may not be sensitive enough to detect all cases of Factor V Leiden mutation. Therefore, genetic testing for the Factor V Leiden mutation is often recommended for a definitive diagnosis. Furthermore, the test's sensitivity can be affected by various factors, including the presence of other coagulation disorders, anticoagulant therapy, and the specific reagents used.