Patients taking the medication warfarin generally must undergo blood testing between once a week and once a month, as directed by the attending physician. Patients who use one of the three newer blood thinners don’t need regular testing, according to WebMD. Still, critics have questioned whether regular testing should be required for at least one of the newer drugs.

In 1954, the Food and Drug Administration approved the use of warfarin to help lower the risk of blood clots leading to stroke. It said people using warfarin must undergo regular blood tests to enable their physician to determine the correct dosage of the drug for them.

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The test determines the patient’s International Normalized Ratio (INR), which helps the physician determine how fast the patient’s blood is clotting and whether his or her medication dosage needs to be changed, said WebMD. Illness, diet, medication changes, and physical activities may affect the INR.

Between 2010 and 2013, the FDA approved the use of blood thinners Pradaxa, Xarelto, and Eliquis to treat atrial fibrillation. Warfarin works by making the blood less likely to clot by blocking the body's capacity to recycle vitamin K, which it uses to form clots.

With less vitamin K in circulation, blood takes longer to clot, but patients need constant testing to determine dosage. The new drugs don't affect vitamin K, and constant monitoring isn't needed.

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When Pradaxa was approved by the FDA in 2010, a major selling point was that it didn't require frequent blood tests, and according to healthinaging, regular blood testing also isn’t required for users of Xarelto and Eliquis.

Pradaxa, Xarelto and Eliquis were found in clinical trials to be equal to or more effective than warfarin, according to WebMD, but the three new drugs also are much more expensive. A typical dose of Pradaxa costs about $300 a month, compared to $4 a month for a typical dose of warfarin.

In 2014, the Institute for Safe Medication Practices questioned the assertion by Pradaxa producer Boehringer Ingelhim that patients didn’t need regular blood-level monitoring. That institute contended they had data covering several years showing the amount of anti-coagulation [blood thinning] varied from patient to patient more than fivefold.

Boehringer Ingelheim responded that they had also conducted studies and concluded that more frequent monitoring wasn't needed.


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