How the Alere INRatio Works
The full name of the device is the Alere INRatio PT/INR monitor system. It is used by patients who are on the blood thinning drug warfarin, marketed as Coumadin. The INRatio is designed to allow doctors, caregivers and/or patients to test how fast the patient’s blood clots so they can determine how well the drug is working. The “PT” stands for prothrombin time, which measures the way the body reacts when a blood vessel rupture occurs. The “INR” portion of the device name stands for International Normalized Ratio, a reading given in seconds that shows how long it takes for blood plasma to clot.
These types of readings were once only available through outside laboratories, making it very inconvenient for many patients to take warfarin. However, the INRatio and similar devices now make getting results as simple as pricking a finger.
An INR level of between 2-3 will allow the blood of most patients taking warfarin to clot properly, although the number is typically around 2.5-3.5 for patients at higher risk of developing dangerous blood clots.
The problem with the INRatio system is that, in many instances, patients were getting readings that were grossly inaccurate. For instance, it could show that a patient is in the safe range (2-3) when his or her actual INR level could be as high as 14.5 or more. The higher the INR, the thinner the patient’s blood – making him or here highly susceptible to a severe, even deadly, bleeding event.
Well before Inverness Medical Innovations, Inc. (the company that eventually became Alere) purchased HemoSense in 2007, the U.S. Food and Drug Administration (FDA) had already sent two warning letters to HemoSense, in 2005 and 2006. The FDA was alleging in the letters that HemoSense had failed to properly act on reports that the INRatio gave erroneous results.