APTT Test (Activated Partial Prothrombin Time)

APTT (activated partial prothrombin time) is a kind of laboratory test that is used to monitor clotting and bleeding problems. Blood creates clots if a damage occurs in the vessel wall to prevent blood loss. Some coagulation factors are needed for  clotting. APTT test measures the passed time for clotting and also used to diagnose clotting problems.

Factors that may affect blood clotting time

  • Blood thinner medicines like heparin
  • Decreased levels of clotting factors
  • Lack of some clotting factors
  • Presence of some components that prevents clotting factors; inhibitors

Clotting factors that are related with APTT test

A problem in factors; I, II, V, VIII, IX, X, XI, XII  causes changes in APPT test result

Purpose; why the APTT test is done?

  • Determination the cause of an abnormal bleeding
  • Determination the cause of bruising and reddening on the skin
  • Monitoring the absence of blood clotting factors
  • Determination of the conditions that may cause problem in blood clotting
  • Checking any clotting problems before surgery
  • Monitoring the heparin therapy
  • Monitoring the liver whether it is working normal or not
  • Finding the cause of blood in urine
  • Diagnosing the cause of frequent nosebleeds
  • Monitoring the cause of prolonged-heavy menstrual period

Production of clotting factors

Most of the blood clotting factors are produced by liver. Their levels decrease in a liver disease and blood clotting problems occur so abnormal bleedings may be seen.

How the APTT test is done?

APTT test is done in a tube of blood sample. Your nurse/technician will insert a needle in a vein that is inside of your elbow or on the back of your hand. He/she will draw blood into  the test tube. You may feel a little pain for a few seconds during the process. All blood collection takes 1-2 minutes.

Factors that may affect APPT test result

Same as other clotting tests, APPT test is done in a special blue colored test tube. This tube contains anticoagulants inside because blood must not be clotted for a proper APTT result. Blood level must be in a certain level in the test tube because anticoagulants are prepared for a certain amount of blood. Test tube’s blood level is so important for a proper APTT test result

Also some medicines and supplements may affects your APTT test result ;


Vitamin C




APTT test normal range

APTT normal value: 25-36 seconds

High APTT test result

Higher than 36 seconds is an increased APTT value and mean;

  • Absence of some coagulation factors/coagulation disorders; von Willebrand disease, hemophilia
  • Liver disease
  • Kidney disease
  • Blood thinner usage
  • Malabsorption
  • Vitamin K deficiency
  • Leukemia


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