Application of 3-D Δ check graphs to HbA1c quality control and HbA1c utilization

Abstract

Δ checking is a laboratory information system (LIS)-based tool that detects patient and laboratory quality control errors. By using hemoglobin A1c (HbA1c) data, we developed a novel approach to summarizing and presenting patient Δ values to address limitations of current Δ check algorithms. Δ values were calculated from intrapatient pairs of HbA1c (n = 55,327) measured during 2 years in a single referral or a university hospital laboratory. Three-dimensional Δ-time (ΔT) and percentile limit graphs were constructed. Cumulative distribution function analysis was used to explore clinical utilization. The ΔT graphs showed that HbA1c Δ values increase asymmetrically over time. Although the 2.5 to 97.5 and 5.0 to 95.0 percentile Δ check limits were similar for both sites, the referral laboratory's 0.5 to 99.5 percentile limits were wider. For acute patient care environments, we recommend limits of -3.5% and 1.8% for measurements between 0 and 60 days and -4.0% and 2.0% for measurements between 60 and 120 days. For the outpatient environment, we recommend limits of -4.2% and 2.1% and 5.0% and 2.5% for measurements between 0 and 60 days and 60 and 120 days, respectively. Δ checking can be significantly improved with customization of limits set by population and interobservation period. Because LIS systems are incapable of these customizations, customers must become advocates for these modifications. © American Society for Clinical Pathology.