Normal activated partial thromboplastin time (aPTT) in a blood test

Each laboratory must establish its own normal range for activated partial thromboplastin time (aPTT) in a blood test. These ranges depend on the makeup of the local population, the technologies used and the accuracy of the measurement. There may be also slight differences in the normal levels according to age, gender, race or ethnic origin, geographic region, diet, type of sample and other relevant status.

Your doctor will study the results along with your medical record, screenings, physical condition, symptoms and any other relevant information about your situation.

There are some circumstances that may alter the normal ranges described above:

• There are different phospholipid reagents or coagulation factor activators that may be added to the blood sample to perform the activated partial thromboplastin time test. For this reason, the normal range may be differ from lab to lab.
• If a patient is taking anticoagulant medication, such as heparin, the aPTT therapeutic range values are 2–2.5 times above the normal range.
• Some types of antibodies present in the blood (lupus anticoagulant factor or antiphospholipid antibodies) may attack coagulation factors and increase the activated partial thromboplastin time (aPTT).

The activated partial thromboplastin time (aPTT) is the amount of time that a blood sample takes to clot when calcium, a phospholipid reagent (such as cephalin) and a coagulation factor activator (kaolin, silica, etc.) are added to the specimen. The aPTT is measured in seconds.

The aPTT is a measurement of the efficacy of the intrinsic coagulation pathway. The blood clotting process is a multistep activity known as coagulation which main objective is to stop a hemorrhage.

The coagulation process depends on the coagulation factors. Coagulation factors are proteins that work together to form a blood clot. There are 13 main proteins involved in the coagulation cascade. The activated partial thromboplastin time (aPTT) is useful to test the clotting factors VIII, IX, XI, and XII.

The activated partial thromboplastin time (aPTT) test is part of a coagulation panel workup. When aPTT is performed in conjunction with a test called prothrombin time (PT), a further clarification of coagulation defects is possible. The aPTT and PT will detect 95% of coagulation abnormalities.

The aPTT test may be ordered for different reasons:

• As part of a presurgical screen to know if there is any blood clotting disorder.
• When a patient has excessive bleeding or bruising.
• To monitor anticoagulant therapy, for example, the heparin therapy. Heparin is used to treat patients who are at high risk of thrombosis and to treat those who have already developed blood clots, especially in postsurgical settings.

A shortened activated partial thromboplastin time (aPTT) has no diagnostic meaning, but it may be due to extensive cancer, when the liver is not involved or after an acute hemorrhage.

The following values are considered to be normal values:

IMPORTANT: These levels are expressed in seconds. They are an example of a healthy man/woman of about 40 years old with no known disease and not taking any medication. The ranges can be different depending on the laboratory or on your personal circumstances.