I-STAT INR Accuracy Questioned
I-STAT (Abbott Point of Care) is a popular device for point of care testing that is used in hospitals to provide quicker turnaround time and expedite clinical decision making. I-STAT INR cartridges are used to determine if a patient presenting to the ED with an ischemic stroke can receive tissue plasminogen activator or if a patient anticoagulated with warfarin can undergo an emergent invasive procedure.
Recently, I compared the INR results of patients treated with warfarin who were simultaneously tested with a fingerstick specimen on an I-STAT at the bedside and a venipuncture specimen on a Stago STAR coagulation analyzer located in the main clinical laboratory.
This study demonstrated significant INR differences between I-STAT and STAR. These results were much more discrepant than the results published in the I-STAT Prothrombin Time/PT packgage insert that compared I-STAT to STA Compact. Even more disconcerting was that the bias was inconsistent throughout the therapeutic range. For example:
- ISTAT INR was as much as 0.5 lower than STAR when the STAT INR is <2.0
- ISTAT INR was as much as 0.5 higher than STAR when STAR INR is between 2.0 and 2.8
- ISTAT INR was as much as 2.0 lower than STAR when STAR INR is >2.8
This small single study suggests that clinicians cannot make accurate clinical decisions based on I-STAT INR results. I have decided to discontinue bedside INR testing with ISTAT until this discrepancy has been resolved. I hope the release of this preliminary data will prompt other clinical laboratories to review their results.
