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Miscellaneous Hematology Tests |
Reference Range |
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PT |
11-13 seconds (varies with reagent lot number) |
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PT (Prothrombin Time) measures how long it takes for a clot to form in a blood sample. It may be ordered in patients with bleeding problems or unexplained bruising to narrow down the possible cause; a prolonged PT can indicate deficiency or insufficiency in one or more clotting factors. A PT may also be ordered prior to surgery; a prolonged PT can indicate a bleeding disorder that may prevent surgery. Because it measures clotting factors affected by blood-thinning drugs, the PT is also used to monitor patients on coumadin. For patients on coumadin, the goal is to elevate the PT so that it is within a therapeutic range, depending on the goal of therapy. |
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INR |
Therapeutic Range: 2-4 |
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INR (International Normalized Ratio) is a calculation based on a patient's PT result and a factor that varies with the PT reagent. In this way, results used to monitor patients on coumadin are standardized and not affected by the variability between reagent sensitivities. |
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PTT |
19-32 seconds (varies with reagent lot number) |
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PTT (Partial Thromboplastin Time) measures how long it takes for a clot to form in a blood sample. It measures clotting factors not measured by the PT test. The PTT may be ordered in patients with bleeding problems or unexplained bruising to narrow down the possible cause; a prolonged PTT can indicate deficiency or insufficiency in one or more clotting factors. It may also be ordered prior to surgery to ensure there are no bleeding disorders. |
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