Question

What is the difference between PT, INR and PTT?

Answer 1

Hint: The Prothrombin Time (PT), the Partial Thromboplastin Time (PTT) and International Normalized Ratio (INR) are the three tests for determining the extent of clotting an individual’s blood will undergo. These tests are done for those experiencing frequent nose bleeds, heavy and prolonged menstruation, painful swollen joints, easy bruising and bloody urine among others. The tests are also administered in case of a surgical operation according to the nature of the surgery.

Complete answer:

Prothrombin Time (PT)	Partial Thromboplastin Time (PTT)	International Normalized Ratio (INR)
The Prothrombin Time test is recommended to test individual plasma’s ability to form clots.	The Partial Thromboplastin Time is primarily performed to determine whether the heparin therapy (a blood thinning therapy) is effective.	International Normalized Ratio (INR) came into being to standardize the results of the PT test.
The reference range for the test is usually between 12-13 seconds.	The normal range of a PTT test is 30-45 seconds (this can vary slightly from lab to lab).	----
In PT sodium acts as an anticoagulant along with the calcium in the blood sample. The blood cells are separated from the plasma by centrifugation after it is mixed. A sample of this blood is extracted and placed in a measuring test tube along with an excess of calcium in a phospholipid suspension.	In PTT decalcified blood is centrifuged to get plasma and then activating substances like calcium are added to initiate the intrinsic pathway of coagulation cascade.	The INR is the ratio of the patient’s prothrombin time to a normal sample, raised to the power of an ISI value for the analyst system being used. The ISI value is the International Sensitivity Index value assigned to the tissue factor that the particular manufacturer produces. It indicates how much a batch of tissue factor compares to an international reference tissue factor.INR = [PT (test) ÷ PT (normal)] ^ ISI
A PT within 11-15 second range indicates normal clotting factors whereas a PT exceeding that range indicates deficiency of the clotting factors.	A prolonged PTT time indicates liver problems, anticoagulation therapy and other diseases whose symptoms are poor clotting.	----
PT follows the external pathway of the coagulation cascade.	PTT follows the intrinsic pathway of the coagulation cascade.	----

Note:
Tissue factor is a protein present in subendothelial tissue and leukocytes. Also called platelet tissue factor, factor III or CD142, it initiates thrombin formation from zymogen prothrombin. PT test and PTT test are similar and both are administered to determine the body’s ability to form clots while bleeding. There are two pathways of coagulation cascade: intrinsic and extrinsic. The intrinsic pathway is activated through exposed endothelial collagen and the extrinsic pathway is activated by the tissue factor released by endothelial cells after external damage.