Application of 3-D Δ Check Graphs to HbA1cQuality Control and HbA1cUtilization

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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 (n = 55,327) measured during 2 years in a single HbA1c referral or a university hospital laboratory. Three-dimensional Δ -time (Δ T) and percentile limit graphs were constructed. Cumulative distribution function analysis was used to explore clinical utilization. The Δ values T graphs showed that HbA1c 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.

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