Evaluation of the i-STAT point-of-care capillary whole blood prothrombin time and international normalized ratio: comparison to the Tcoag MDAII coagulation analyzer in the central laboratory.

BACKGROUND

Point-of-care devices for performing a prothrombin time/international normalized ratio (PT/INR) using capillary blood samples are being increasingly used to monitor patients receiving anticoagulation therapy. However, the performance of some devices has been shown to be suboptimal and there are only limited published data comparing specific devices to various central laboratory coagulation analyzers. We report an evaluation of the iSTAT PT/INR with a comparison to the Tcoag MDA II analyzer.

METHODS

We obtained simultaneous capillary/venous samples on 20 healthy volunteers for a normal range study and on 50 anticoagulated patients for a clinical evaluation. Testing was performed by phlebotomists. We also obtained 68 near simultaneous capillary/venous test results for assessment of performance by non-laboratory personnel. The criteria for determining clinical equivalence of the iSTAT to the MDA II were (1) same clinical category (subtherapeutic INR<2, therapeutic INR 2-3, and supratherapeutic INR>3) or (2) paired values within ≤ 0.4 INR.

RESULTS

Forty nine of 50 patient sample pairs collected by phlebotomists showed acceptable clinical agreement. Sixty one (61) of 68 patient sample pairs collected by nurses showed acceptable agreement. In all discordant cases the differences were minor and would have resulted in either no or minimal change in therapy.

CONCLUSIONS

The iSTAT PT/INR compares well to the MDA II when performed by phlebotomists or nurses.