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The partial thromboplastin time (PTT), also known as the activated partial thromboplastin time (aPTT or APTT), is a blood test that characterizes coagulation of the blood. A historical name for this measure is the Kaolin-cephalin clotting time ( KCCT ), [ 1 ] reflecting kaolin and cephalin as materials historically used in the test.
The aPTT-based APC resistance test involves a modified aPTT test performed in the presence and absence of activated protein C (APC). [1] [5] The ratio of these aPTT values is calculated and is called the APC sensitivity ratio (APCsr) or simply APC ratio (APCr). [1] [5] This ratio is inversely related to the degree of APC resistance. [7]
The prothrombin time ratio is the ratio of a subject's measured prothrombin time (in seconds) to the normal laboratory reference PT. The PT ratio varies depending on the specific reagents used, and has been replaced by the INR. [3] Elevated INR may be useful as a rapid and inexpensive diagnostic of infection in people with COVID-19. [4]
Laboratories usually calculate their own ranges, based on the method used and the results obtained from healthy individuals from the local population. Variability arises from differences in thrombin concentration, dilution of plasma, presence and/or concentration of calcium ions, as well as the influence of analyser type. [ 5 ]
Fresh normal plasma has all the blood coagulation factors with normal levels. If the problem is a simple factor deficiency, mixing the patient plasma 1:1 with plasma that contains 100% of the normal factor level results in a level ≥50% in the mixture (say the patient has an activity of 0%; the average of 100% + 0% = 50%). [3]
Thromboelastography (TEG) is a method of testing the efficiency of blood coagulation.It is a test mainly used in surgery and anesthesiology, although increasingly used in resuscitations in emergency departments, intensive care units, and labor and delivery suites.
Diagnostic odds ratios less than one indicate that the test can be improved by simply inverting the outcome of the test – the test is in the wrong direction, while a diagnostic odds ratio of exactly one means that the test is equally likely to predict a positive outcome whatever the true condition – the test gives no information.
References range may vary with age, sex, race, pregnancy, [10] diet, use of prescribed or herbal drugs and stress. Reference ranges often depend on the analytical method used, for reasons such as inaccuracy , lack of standardisation , lack of certified reference material and differing antibody reactivity . [ 11 ]
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