Utilization of Assay Performance Characteristics to Estimate Hemoglobin A1c Result Reliability. (1st August 2014) - Woodworth, Alison
Abstract: BACKGROUND: Allowable total error (TEa ) goals for hemoglobin (Hb) A1c require minimal assay imprecision and bias and implementation of a robust QC monitoring program. Here, we compare the combined influence on the risk of reporting unreliable results of TEa goals, a routine QC practice, and assay performance characteristics of 6 Hb A1c instruments across 4 academic medical centers. METHODS: The CLSI protocols EP-5 and EP-9 were applied to investigate Hb A1c result imprecision and bias on the Variant II Turbo and Variant II (Bio-Rad), G8 (Tosoh), Capillarys 2 Flex Piercing (Sebia), COBAS Integra 800 (Roche), and DCA Vantage (Siemens). Patient-weighted σ values and the risk of reporting unreliable Hb A1c results were determined for each assay at TEa specifications of 5%, 6%, and 7%. RESULTS: A large range of patient-weighted σ values spanning 0.5 orders of magnitude at a 6% TEa was observed. Although imprecision for all instruments was <3%, bias impacted the majority of the σ changes observed. Estimates for reporting unreliable results varied almost 500-fold based on analytical performance alone. CONCLUSIONS: Considerable differences in the probability of reporting unreliable Hb A1c results between different NGSP (formerly the National Glycohemoglobin Standardization Program)-certified platforms were observed. At a 6% TEa, our study indicates all but the Capillarys 2 Flex Piercing requires that the maximum affordable QC be run. Risk estimates for individual laboratories' Hb A1c methods can be used to assess QC practices and residual risk of an unreliable Hb A1c result.