From the Guidelines
aPPT, or activated Partial Thromboplastin Time, is a blood test that measures how long it takes for blood to clot, specifically evaluating the intrinsic and common pathways of the coagulation cascade. This test is commonly used to monitor heparin therapy, screen for certain bleeding disorders, and assess the function of coagulation factors. The normal range for aPTT is typically 25-35 seconds, though this may vary slightly between laboratories [ 1 ]. When a patient is on heparin therapy, the target aPTT is usually 1.5-2.5 times the normal control value. Prolonged aPTT results may indicate conditions such as hemophilia, liver disease, vitamin K deficiency, or the presence of lupus anticoagulant [ 1 ]. The test works by adding an activator (such as kaolin) and phospholipids to plasma, then measuring the time until clot formation occurs. Understanding aPTT results is crucial for diagnosing bleeding disorders and ensuring appropriate anticoagulation therapy management. Some key points to consider when interpreting aPTT results include:
- The test is sensitive to the effects of heparin and other anticoagulants [ 1 ]
- Prolonged aPTT results may require further evaluation to determine the underlying cause [ 1 ]
- The test is an important tool for monitoring patients on heparin therapy and adjusting their treatment as needed [ 1 ]
From the Research
Definition of aPPT
- Activated partial thromboplastin time (aPPT or APTT) is a coagulation assay that measures the time it takes for blood to clot 2.
- The aPPT test is based on the principle that in citrated plasma, the addition of a platelet substitute, factor XII activator, and CaCl2 allows for the formation of a stable clot 2.
Clinical Use of aPPT
- The aPPT is commonly used to monitor anticoagulant therapy, particularly in patients with heparin-induced thrombocytopenia (HIT) or disseminated intravascular coagulation (DIC) 3, 4, 5.
- The test is also used to evaluate the effectiveness of direct thrombin inhibitors (DTIs) such as argatroban and bivalirudin 4.
- However, the use of aPPT to monitor DTI therapy has been questioned due to concerns about its accuracy and reliability 4.
Limitations of aPPT
- The aPPT can be confounded by various factors, including the presence of antibodies against platelet factor 4 (PF4)/heparin complexes 3, 5.
- The test can also be affected by consumptive coagulopathy, which can lead to inaccurate results 3, 5.
- Studies have shown that the aPPT may not be a reliable indicator of anticoagulation in patients with pulmonary embolism 6.