Performance Characteristics of Hemolysis Index on Roche Cobas 8000 Automated Analyzers Including Correlation of Hemolysis Index With Free Hemoglobin Concentration in Plasma

Abstract

Hemolysis is a common specimen abnormality that can interfere with many laboratory tests and lead to erroneous results and interpretations and to inappropriate medical decisions. Determination of the hemolysis index (HI), a dimensionless measure, is one method to assess for this interference. Our goals in this study were to: 1) validate our HI measurements as we transition to new core laboratory automated chemistry instruments (previous, Roche Modular [Roche Diagnostics, Indianapolis, IN]; new, Roche Cobas 8000); 2) determine the impact of matrix differences on HI in serum vs plasma and 3) quantify the HI in plasma relative to free hemoglobin concentration, allowing standardization and comparison of HI in common units. Studies were performed to determine the linearity, precision, and comparability of HI on the cobas 8000 system. Matrix differences were assessed by mixing studies. Samples with a range of HI values were also analyzed for free hemoglobin concentration by an external reference laboratory. Performance characteristics of the HI on the cobas 8000 were as follows: %CV = 5% (mean = 19), %CV = 1.1% (mean = 295); linear in plasma for values from 8 to 420; comparison with the Modular P800: R 2 = .99, slope = 1.0. Mixing studies showed recovery between 93%-102%. The plasma hemoglobin concentration shows a consistent, linear relationship with the HI over a range of HI that is typically encountered in our laboratory. This relationship was comparable across the various Roche analyzers, including the cobas 8000, used in our study. The linear fit provides for converting a unitless measure into a standardized quantity; one HI unit corresponds to 1.25 mg/dL. Hemolysis index determinations are comparable in previous and newer generations of Roche chemistry platforms. Our existing interference HI cutoffs can be maintained on the cobas 8000, and can be used for both serum and plasma samples.