Reference range of hemolysis index in serum and lithium-heparin plasma measured with two analytical platforms in a population of unselected outpatients.

BACKGROUND: The hemolysis index (HI) is now available in several laboratory analyzers, but doubts remain about the thresholds for suppressing test results, the degree of standardization among different instrumentations and the use of different reference ranges in different biological matrices. This study was hence planned to establish the reference ranges of HI in serum and lithium-heparin plasma in a population of unselected outpatients, using two analytical platforms. MATERIALS AND METHODS: We analyzed the HI in serum and lithium-heparin samples collected from 135 unselected outpatients, and we also defined the relative reference ranges according to Clinical and Laboratory Standards Institute (CLSI) recommendations. Samples were collected in the morning by expert nurses, using straight needle venipuncture. The HI in serum and lithium-heparin plasma was assessed with Roche Cobas c501 and Siemens Dimension Vista 1500. RESULTS: The median concentration of cell-free hemoglobin was significantly higher in serum than in lithium-heparin plasma when measured with Cobas c501, but not with Dimension Vista 1500. After categorizing values according to cell-free hemoglobin thresholds, the agreement between instruments was 0.75 (p<0.01) for serum and 0.95 (p<0.01) for lithium-heparin plasma. The upper limits calculated according to CLSI document C28-A3 were 0.22g/L for Roche Cobas c501 and 0.25g/L for Siemens Dimension Vista 1500 in serum, whereas they were 0.13g/L for Cobas c501 and 0.10g/L for Dimension Vista 1500 in lithium-heparin plasma. CONCLUSIONS: According to our data, different thresholds of cell-free hemoglobin should be used between serum and lithium-heparin plasma for monitoring phlebotomy practice.