Activated Partial Thromboplastin Time (APTT)

The measurement of activated partial thromboplastin time (APTT) in plasma is used to monitor heparin therapy (unfractionated heparin). It is also a complementary test to check for certain coagulation factor deficiencies and detect specific coagulation inhibitors, such as lupus anticoagulants.

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Hemostasis involves many steps, including properly functioning various clotting factors and other substances. The partial thromboplastin time (PTT) and activated partial thromboplastin time (APTT) are used to assess how well the blood clotting process works. This test helps detect blood clotting disorders caused by either a deficiency or defective function of the clotting factors that make up the intrinsic system. These factors include I, II, V, VIII, IX, X, XI, and XII. Typical APTT values ​​may reflect normal blood clotting function, but mild deficiencies of a single clotting factor may be present. The decrease in a single clotting factor is not reflected in the APTT value until the decline reaches 30-40% of its regular activity.

The PTT (partial thromboplastin time) is also used to monitor heparin therapy. Heparin inactivates prothrombin and prevents the formation of thromboplastin. Thus, in conditions in which preventing clot formation is necessary, heparin is usually given as a continuous intravenous infusion. The patient's response to this anticoagulant therapy must be appropriate and sufficient to prevent clot formation but not so great as to cause spontaneous bleeding. The PTT can be used to monitor this delicate balance.

The PTT involves measuring the time it takes for a clot to form in a plasma sample to which calcium and partial thromboplastin are added. If various chemicals are added to standardize and speed up the test, the result is the activated partial thromboplastin time, or APTT. If the APTT is more significant than 100 seconds, the patient is at high risk of spontaneous bleeding.

In the event of a heparin overdose with subsequent bleeding, the antidote is protamine sulfate.

Possible Interpretations of Pathological Values
 

• Increase: The leading causes are genetic or acquired deficiency of blood coagulation factors IX, X, XI, XII, and/or factor V or II. These deficiencies usually need to be below 30% - 40% of normal levels of coagulation factors to produce an increased APTT and bleeding tendencies, as in hemophilia A. Increased times are associated with deficiencies in high molecular weight (HMW) kininogen and Fletcher factor (prokallikrein). Longer times also occur during placental abruption, cardiac surgery, hypothermia, cirrhosis, disseminated intravascular coagulation, dysfibrinogenemia, fibrinolysis, Fitzgerald factor deficiency (severe), hemorrhagic disease of the newborn, hypofibrinogenemia, liver disease, hypoprothrombinemia, presence of anticoagulants, lupus anticoagulant, von Willebrand disease, patients on hemodialysis. Medications: Alcohol, anistreplase (thrombolytic agent), hydroxycoumarin (perissia), chlorpromazine, codeine, eptifibatide, heparin, methotrexate, phenothiazines, salicylates, warfarin, valproic acid
• Decrease: Shorter times occur in Fletcher factor abnormalities not associated with bleeding and in which thromboembolism may occur. A shorter APTT in patients with chest pain is associated with an increased risk of acute myocardial infarction.

Measurement of activated partial thromboplastin time (APTT) is performed by taking a blood sample, which can be done:

• At Diagnostiki Athinon - By taking a blood sample in Diagnostiki Athinon. There is no need for prior fasting. Book your appointment in real-time and purchase the test online