PT, PTT, INR
Prepared by zeyad H Alkahlout. (B.S.N, RN MPH)
Illustration of PT, PTT and INR blood tests:
Before you have surgery your doctor may order blood tests to determine how quickly
yourblood clots. This group of tests is known as a coagulation study; individually
these tests are commonly referred to as a PT (Prothrombin Time), PTT (Partial
Thromboplastin Time), and INR(International Normalized Ratio).
During some surgeries it is important that the blood not clot as quickly as normal, and
medications may be given to slow the clotting time. Drugs commonly used to slow
clottinghave a variety of names, but Heparin, Coumadin, Lovenox and Warfarin are
among the most common. In other cases, the patient may not clot quickly enough, and
steps may be taken to make the blood toclot more quickly.
1. Prothrombin Time Blood Test (PT)
This test is done to evaluate the blood for its ability to clot. It is often done before
surgery to evaluate how likely the patient is to havea bleeding or clotting problem
during or after surgery.
Normal PT Values: 10-12 seconds (this can vary slightly from lab to lab)
Common causes of a prolonged PT include vitamin K deficiency,hormones drugs
including hormone replacements and oral contraceptives, disseminated intravascular
coagulation (a serious clotting problem that requires immediate intervention), liver
disease, and theuse of the anti-coagulant drug warfarin. Additionally, the PT result
can be altered by a diet high in vitamin K, liver, green tea, dark green vegetables and
2. Partial Thromboplastin TimeBlood Test (PTT)
This test is performed primarily to determine if heparin (blood thinning) therapy is
effective. It can also be used to detect the presence of a clotting disorder. It does not
showthe effects of drugs called “low molecular weight heparin” or most commonly
by the brand name Lovenox.
Normal PTT Values: 30 to 45 seconds (this can value slightly from lab to lab)
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