At some time or another, many of us are confused with the different options available for the laboratory testing of Prothrombin Time (PT) and Partial Thromboplastin Time (PTT), so here’s a little ‘cheat sheet’ to refresh your memory:
* Prothrombin Time (PT) measures how long it takes blood to clot & validates the presence of five different blood clotting factors. PT should be around 12–15 seconds. If the PT is low when a patient is on Coumadin, then the dose is not therapeutic and needs to be increased.
* Partial Thromboplastin Time (PTT) or Activated Partial Thromboplastin Time (aPTT):measures other clotting factors & indicates the therapeutic level of Heparin. If the PTT is low and the patient is on Heparin, then the dose is not therapeutic and needs to be increased. A sliding scale is used to adjust the Heparin dosage based on aPTT results.
* International Normalized Ratio (INR) is used to monitor the effectiveness of anticoagulants. Most laboratories report PT results that have been adjusted to the INR for patients on anti-coagulant drugs. These patients should have an INR of 2.0-3.0. For patients at high risk of clot formation, the INR needs to be higher (2.5 to 3.5).
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