This question recently appeared in the Diagnostic Health Equity site, managed by Tamara Lobban-Jones. “My doctor said my PT/INR was a little high. What does that actually mean for me, and should I be worried about bleeding more easily? I’ve been on a blood thinner for a while, but my PTT keeps coming back different every test. Why does it change so much?”
My (Geo) answer: We use the term “blood thinner” to describe therapeutic anticoagulants, such as warfarin, Eliquis, and Xarelto. These therapies don’t actually “thin” the blood. Instead, they control the activity of our normal blood-clotting proteins, called clotting factors. Anticoagulants are used to prevent blood clotting in people who have an elevated clot risk, or to reduce the risk of additional clotting in people who have experienced at least one blood clot in a vein or artery. Warfarin (also known as Coumadin) is an effective oral anticoagulant that has been available since 1952. Your provider arranges to monitor warfarin therapy periodically to confirm that its plasma concentration is within the therapeutic range. Providers choose periodic testing using the prothrombin time and international normalized ratio (PT/INR). The target therapeutic range is 2–3. If your PT/INR result is over 3, you have an increased risk of bleeding, and if below 2, your risk of clotting is elevated. In either event, your health care team will recommend a change in your dosage. Your team may include a dietitian who recommends a diet that minimizes PT/INR changes, as certain foods, especially green vegetables, may interfere with warfarin. The partial thromboplastin time (PTT) is often run alongside the PT/INR; however, it is not used to monitor warfarin. The PTT provides valuable additional information about your coagulation system. Because it is a sensitive test with a wide normal range, typically ~25–35 seconds, the PTT tends to vary by a few seconds from time to time. You will want to communicate with your provider whenever the PTT and/or the PT/INR is out of range.
Our answers are developed for intelligent laypeople, and I’m sharing this in case you have additional suggestions for updates. In which case, please comment below.
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