The FDA issued a Class I recall on test strips used to measure a patient’s international normalized ratio (INR) due to reports that ranges found through its product differed significantly from results in tests performed in a laboratory.

Alere is voluntarily recalling its INRatio2 PT/INR Professional Test Strips after receiving complaints that some patients’ INR was 3.1 to 12.2 units lower when tested with the strips compared with results by a central laboratory. Physicians and other healthcare professionals are advised to stop using the test strips immediately.

INR in patients on warfarin must be monitored to ensure the safety and effectiveness of the blood-thinning therapy. The test strips are used to determine if a patient’s INR is within the therapeutic range.

The Waltham,Mass.-based company received nine serious adverse event reports. Three reports described bleeding associated with patient deaths. Alere said it has not determined the root cause to identify patient conditions or circumstances that may contribute to the discrepancy.

Cardiologists, emergency medicine staff and others should find an alternate method to monitor patients’ INR. Alere plans to transition customers from the INRatio2 PT/INR Professional Test Strips (PN 99008G2) to the Alere INRatio PT/INR Test Strip (PN 100139). The recall does not include the Alere INRatio PT/INR Test Strip (PN 100071), with is used for home monitoring.

The FDA is investigating the adverse event reports. Physicians and patients should report any adverse events related to the test strips to the FDA.