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How to interpret PT results?
When interpreting the results of a prothrombin time, we need to see the laboratory’s reference values for a more accurate comparison. These normal reference values are set according to the reactants used to perform the test. Every reactant has different reference values, and that’s why each laboratory provides a useful table with normal levels.
When you get a prolonged time (a higher number than the reference), it means that the blood is taking too long to clot. In this case, it is probably because one or more coagulation factors evaluated by prothrombin time are compromised.
When you get a shortened time (a lower number than the reference), it means that the blood creates clots very rapidly, and this is not normal, either.
Comparing prothrombin time (PT) with partial thromboplastin time (PTT) is handy to suspect a diagnosis. For example, a prolonged PT with a normal PTT is found in vitamin K insufficiency, liver diseases, a genetic defect on factor VII, and as a result of warfarin therapy. PT and PTT can be both compromised in severe cases of liver disease and a warfarin overdose. But if PT is normal and PTT is prolonged, it is probably because of lupus anticoagulant disease or an auto-antibody destroying a coagulation factor (usually factor VIII).
