Partial Thromboplastin Time (PTT)

Clinical definition of the PTT test
The partial thromboplastin time (PTT) is a screening test  that evaluates  the time it takes for the blood to clot by measuring the duration taken ( in seconds) for a clot to form in a test tube when specific substances( reagents) are added to a sample of plasma. A clot is a thick lump of blood that is produced to seal leaks, wounds, cuts and scratches and prevent excessive bleeding. When body tissue(s) or blood vessel walls are injured, bleeding occurs and a process called hemostasis occurs. About 12 blood clotting factors are needed for blood to clot ( coagulation) By measuring the time it takes to form the clot, the PTT assesses the amount as well as the function of certain coagulation factors that are part of hemostasis and checks for bleeding problems.

Why is the PTT test done?
Partial Thromboplastin time (PTT) detects all abnormalities in clotting, due to deficiencies in clotting factors or circulating anticoagulants. This test is done to:

  • Find a cause of abnormal bleeding or bruising.
  • Check for low levels of blood clotting factors or coagulation factors such as XII, XI, IX, VIII, X, V, II $ I. The lack of some clotting factors can cause bleeding disorders such as hemophilia.
  • Check blood clotting time before a surgery
  • Check for conditions that cause clotting problems
  • Check to see if the dose of anti-clotting medicines is right
  • To monitor anticoagulant / anti-clotting (heparin) therapy and its dose

What should I do before the PTT test?

Specimen type

Specimen collection procedure

Preparatory instructions before the test *

Plasma (Blood Sample)

Venipuncture -- Collection of blood from a vein, usually from the arm.

No Fasting Required.

No other special preparations required.

*Subjects suffering from any illness or on oral or injectable medications are advised to consult their physician prior to requesting any tests or procedures.

How do I interpret my PTT test results?

*Reference range


26.7 to 37.0 seconds



30-40 seconds


30-40 seconds


1 Month - 1Yr

31.1 -  36.6 seconds

1-5 year

29.8 - 35 seconds

6-10 year

30.8 - 34.8 seconds

11- 16 year

29.4 - 40.4 seconds

Inference: A prolonged aPTT can indicate a deficiency of any of various coagulation factors, including factor XII, XI, IX, VIII, X, V, II and fibrinogen.
‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’

Diseases/conditions related to the PTT test

Other tests related to the PTT test

  • Prothrombin Time (PT)
  • Fibrinogen
  • Thrombin Time
  • Lupus Anticoagulant
  • Activated Clotting Time (ACT)
  • Coagulation Factors
  • Platelet Count
  • Heparin Anti-Xa
  • Von Willebrand Factor
  • Antiphospholipid Antibodies
  • Dilute Russell Viper Venom Time (DRVVT)

Synonyms : Activated Partial Thromboplastin Time (aPTT)
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