Evaluation of point-of-care International Normalized Ratio in sickle cell disease.

Background: Point-of-care (POC) International Normalized Ratio (INR) measurement provides efficient monitoring of warfarin therapy; however, its reliability may be affected in patients with anemia, such as those with sickle cell disease (SCD).

Objectives: To evaluate the correlation of POC-INR to clinical laboratory INR (CL-INR) in SCD and use of a correction factor.

Patient/methods: In this retrospective study, the accuracy of POC-INR compared to CL-INR was evaluated in a cohort of patients with SCD and in a non-SCD Black cohort.

Results: Despite the difference in anemia, the SCD cohort showed a similar percentage of in-range POC-INR values as observed in the non-SCD cohort (37% vs 42%). The SCD cohort was randomly divided to form discovery and validation cohorts. In the discovery cohort, 86% of POC-INRs were in range when the POC-INRs were ˂4.0, but only 24% were in range if POC-INRs were ≥4.0. A linear regression of CL-INR versus POC-INR for POC-INR values ≥4.0 yielded a coefficient of 0.72 (95% confidence interval, 0.69-0.75); Multiplying POC-INR by this correction factor, rounded to 0.7 for ease of use in clinical practice, improved the proportion of in-range POC-INR values ≥4.0 from 24% to 100% in the SCD discovery cohort and from 19% to 95% in the SCD validation cohort. Similar findings applied to analyses of the non-SCD cohort.

Conclusions: POC-INR and CL-INR in patients with SCD are similar when POC-INR is <4.0, and the accuracy of POC-INR values ≥4.0 can be improved by applying an institution-specific correction factor.