The Impact of Hemolysis-Index Thresholds on Plasma and Serum Potassium Measurements

Modern clinical laboratory analyzers measure a hemolysis index (H-index) because test results can be inaccurate when intracellular contents from erythrocytes leak into serum or plasma. In 2020, Roche Diagnostics decreased the H-index from 90/100 to 20 for potassium, recommending that laboratories avoid using specimens with an H-index >20; however, there are a limited number of studies investigating the impact of this recommendation on patient testing.

Out of 113 916 serum or plasma potassium tests performed within a 6-month interval, 72 patients with potentially hemolyzed potassium specimens (H-index >20) and a second non-hemolyzed specimen (H-index ≤20) within 2 h were identified. The clinical impact of decreasing the H-index and the utility of applying a corrective formula for adjusting potassium results were evaluated.

The majority of initial test results either had small differences between original and corrected results that would not have affected clinical management or H-indices above the threshold previously recommended by Roche. We estimated the second sample was reported an average of 3 h 23 min after the initial sample was collected, with 95% CI [2 h 37 min to 4 h 8 min], and the median time delay was 2 h 44 min.

Our analysis does not show a clear benefit from avoiding the use of potassium specimens above an H-index threshold of 20. Our findings suggest these practices may be detrimental in terms of patient safety due to increased turnaround time for a critical analyte.