Prothrombin time (PT)

Clinical definition of the Prothrombin time test
A prothrombin time (PT) test measures the time it takes for a clot to form in a blood sample. A clot is a thick lump of blood that the body produces to seal leaks, wounds, cuts and scratches and prevent excessive bleeding. 12 blood clotting factors are needed for blood to clot (coagulation). Prothrombin or factor II is one of the clotting factors made by the liver. Vitamin K is needed to make prothrombin and other clotting factors. The PT test evaluates, the integrated function and the action of five different clotting (coagulation) factors (I, II, V, VII, and X). It evaluates the body’s ability to produce a clot in a reasonable amount of time. If any factor is missing, deficient, or defective, clotting time is delayed, the PT is prolonged. It is also used to check for bleeding problems.

Why is the Prothrombin time test done?
Prothrombin time (PT) is a blood test that measures the time taken for the liquid portion (plasma) of the blood to clot. Prothrombin test evaluates the ability of blood to clot properly, it is carried out to detect and diagnose a bleeding disorder and monitor the effects of the blood thinning medication warfarin. It is used in conjunction with PTT to evaluate the function of all coagulation factors. The test monitors the clotting ability of people with liver disease or vitamin K deficiency.

What are the common signs/symptoms when the Prothrombin time test is done?

  • Easy bruising
  • Nosebleeds that won't stop
  • Excessive bleeding after dental appointments
  • Heavy menstrual periods
  • Blood in the urine
  • Swollen or painful joints

What should I do before the Prothrombin time test?

Specimen type

Specimen collection procedure

Preparatory instructions before the test *

Serum (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 Prothrombin time test results?


Reference Range*


10 to 15 Seconds


10 – 15 seconds


11 – 14 seconds

New born

Below 17seconds

International normalized Ratio (I.N.R)

2 to 3

Prothrombin ratio


‘*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 Prothrombin time test

Other tests related to the Prothrombin time test

  • Activated Clotting Time (ACT)
  • Partial Thromboplastin Time (PTT)
  • Prothrombin Consumption Time (PCT) 
  • Fibrinogen
  • Coagulation Factors
  • Platelet Count
  • Platelet Function Tests
  • Thrombin Time
  • Bleeding Time (BT)
  • Clotting Time (CT)

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Prothrombin time (PT)

Book Related Tests
  • Prothrombin time (PT)
  • BT (Bleeding Time)
  • Clotting Time (CT)