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Activated partial thromboplastin time (APTT)
Medical expert of the article
Last reviewed: 05.07.2025
Reference values for activated partial thromboplastin time (aPTT)
Activated partial thromboplastin time (APTT) is one of the most valuable general tests for obtaining an idea of the blood coagulation system. APTT is a test that exclusively reveals plasma defects of the intrinsic system of activation of factor X in phase I (prothrombinase formation) of blood coagulation.
Determination of activated partial thromboplastin time is a modification of the test for determining the recalcification time of stabilized blood (plasma). It has a higher sensitivity to the deficiency of plasma coagulation factors (except VII and XIII), however, when using this test it is not possible to detect the insufficiency of the coagulation activity of platelets.
Prolongation of activated partial thromboplastin time (APTT) reflects deficiency of plasma factors (except VII and XIII) and is observed with their significant (below 25-10%) decrease. Prolongation of activated partial thromboplastin time (APTT) indicates prevalence of hypocoagulation.
Reference values: 38-55 s. However, it should be noted that reference values in different laboratories may vary depending on the sensitivity and composition of the diagnostic kits.
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