Test Details


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Activated Partial Thromboplastin Time (APTT), Sodium Citrate Whole Blood

Number of parameters covered 2

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Synonyms/Also Known as

Activated Partial Thromboplastin Time, aPTT

Related tests

PT and INR, Fibrinogen, D-dimer, Thrombin Time, Lupus Anticoagulant Testing, ACT, Coagulation Factors, Platelet Count, Heparin Anti-Xa, Von Willebrand Factor, Antiphospholipid Antibodies

Why get tested?

To investigate a bleeding disorder or a blood clot. To monitor heparin anticoagulant therapy and as part of routine screening before surgery.

When to get tested?

When there is unexplained bleeding, inappropriate blood cloting, or miscarriages frequently, when a person is on heparin anticoagulant therapy and as part of routine screening before surgery.

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Test preparation needed

No special preparation required

About The Test

How is it used
The Activated Partial Thromboplastin Time (aPTT) test is used to investigate if a person has unexplained bleeding or blood clotting. It is usually done with a prothrombin time (PT) test to evaluate hemostasis. Coagulation factors are proteins which are synthesised in the liver and are involved in hemostasis (i.e helps to stop bleeding by forming blood clot, whenever there is injury). As soon as there is injury in the body and it bleeds, the coagulation factors get activated in an order and helps in forming a stable clot which stops the bleeding. This process occurs naturally in the body. If there is deficiency or insufficient quantity of any of the coagulation factor, the natural hemostasis is disturbed. If there is less or no coagulation factor it results in excess bleeding and if there is too much it leads to excess clotting. The Activated Partial Thromboplastin Time (aPTT) test is used to evaluate the coagulation factors of intrinsic and common pathways (factors XII, XI, IX, VIII, X, V, II (prothrombin), and I (fibrinogen), prekallikrein and high molecular weight kininogen). A prothrombin Test is used to evaluate the coagulation factors of extrinsic and common pathway (factors VII, X, V, II, and I (fibrinogen)). By interpreting the results of PT and aPTT tests together, the cause of a bleeding or clotting disorder may be obtained. The aPTT and PT are not diagnostic tests but they provide information on additional tests needed. The Activated Partial Thromboplastin Time (aPTT) test is used to identify coagulation factor deficiency, To detect nonspecific autoantibodies like lupus anticoagulant, to monitor heparin anticoagulant therapy. The other test include PT, thrombin time, platelet count, fibrinogen test, coagulation factor tests. The common causes of a prolonged APTT are as follows : Disseminated intravascular coagulation, Liver disease. Massive transfusion with plasma-depleted red blood cells. Administration of or contaminated with heparin or other anticoagulants. A nonspecific circulating anticoagulant (such as an LAC). The presence of a direct acting anticoagulant drug (e.g. anti-IIa or anti-Xa agents. Deficiency of a coagulation factor other than factor VII.


1. Is the aPTT always used to monitor heparin anticoagulant therapy?

It is used in most of the cases to monitor the heparin anticoagulant therapy but in few cases like open heart surgery where high doses of heparin are used, deep vein thrombosis (DVT) treatment and people with lupus anticoagulant, aPTT test is not reliable.

2. Is aPTT testing compulsory?

The aPTT test is not a routine screening test but is done when there is a family history of abnormal bleeding or clotting or when a person has symptoms, and prior to a surgery or procedure.

3. How can the aPTT value change?

The aPTT value ca ot be changed by lifestyle modifications. In temporary or acute conditions it may return to normal once the cause is resolved.