What is aPTT coagulation tests?

Author: Succeeder    

Activated partial thromboplastin time (activeated partial thromboplasting time, APTT) is a screening test for detection of "intrinsic pathway" coagulation factor defects, and is currently used for coagulation factor therapy, heparin anticoagulant therapy monitoring, and detection of lupus anticoagulant The main means of anti-phospholipid autoantibodies, its clinical application frequency is second only to PT or equal to it.

Clinical significance
It basically has the same meaning as coagulation time, but with high sensitivity. Most of the APTT determination methods currently used can be abnormal when the plasma coagulation factor is lower than 15% to 30% of the normal level.
(1) APTT prolongation: the APTT result is 10 seconds longer than that of the normal control. APTT is the most reliable screening test for endogenous coagulation factor deficiency and is mainly used to discover mild hemophilia. Although factor Ⅷ: C levels can be detected below 25% of hemophilia A, the sensitivity to subclinical hemophilia (factor Ⅷ>25%) and hemophilia carriers is poor. Prolonged results are also seen in factor Ⅸ (hemophilia B), Ⅺ and Ⅶ deficiencies; when blood anticoagulant substances such as coagulation factor inhibitors or heparin levels increase, prothrombin, fibrinogen and factor V, X deficiency also It can be prolonged, but the sensitivity is slightly poor; APTT prolongation can also be seen in other patients with liver disease, DIC, and a large amount of banked blood.
(2) APTT shortening: seen in DIC, prethrombotic state and thrombotic disease.
(3) Monitoring of heparin treatment: APTT is very sensitive to the concentration of plasma heparin, so it is a widely used laboratory monitoring index at present. At this time, it should be noted that the APTT measurement result must have a linear relationship with the plasma concentration of heparin in the therapeutic range, otherwise it should not be used. Generally, during heparin treatment, it is advisable to maintain APTT at 1.5 to 3.0 times that of the normal control.
Result analysis
Clinically, APTT and PT are often used as screening tests for blood coagulation function. According to the measurement results, there are roughly the following four situations:
(1) Both APTT and PT are normal: Except for normal people, it is only seen in hereditary and secondary FXIII deficiency. Acquired ones are common in severe liver disease, liver tumor, malignant lymphoma, leukemia, anti-factor XIII antibody, autoimmune anemia and pernicious anemia.
(2) Prolonged APTT with normal PT: Most of the bleeding disorders are caused by defects in the intrinsic coagulation pathway. Such as hemophilia A, B, and factor Ⅺ deficiency; there are anti-factor Ⅷ, Ⅸ, Ⅺ antibodies in the blood circulation.
(3) Normal APTT with prolonged PT: most bleeding disorders caused by defects in the extrinsic coagulation pathway, such as genetic and acquired factor VII deficiency. Acquired ones are common in liver disease, DIC, anti-factor VII antibodies in blood circulation and oral anticoagulants.
(4) Both APTT and PT are prolonged: most bleeding disorders caused by defects in the common coagulation pathway, such as genetic and acquired factor X, V, II and I deficiency. Acquired ones are mainly seen in liver disease and DIC, and factors X and II may be reduced when oral anticoagulants are used. In addition, when there are anti-factor X, anti-factor V and anti-factor II antibodies in the blood circulation, they are also prolonged accordingly. When heparin is used clinically, both APTTT and PT are prolonged accordingly.