Introduction: The prevalence of diabetes in Trinidad and Tobago (T&T) exceeds 12%. Monitoring of HbA1c is standard of care to assess diabetes control but assay reliability requires high precision and standardization to either DCCT or IFCC values and results should be monitored through proficiency testing (PT). In T&T a developing country there is no existing data on HbA1c precision and accuracy. Johns Hopkins Medicine International and the Diabetes Diagnostic Laboratory, University of Missouri studied the accuracy and precision of HbA1c testing to determine the clinical utility of HbA1c measurements in T&T.
Methods: Sets of ten samples containing blinded duplicates were created from five whole blood pools with HbA1c levels from 5.1 to 9.3% HbA1c and shipped to the five public hospitals and two large volume private laboratories. To assess within-day imprecision, the pooled estimate of the SDs between the duplicates (Sp) was calculated; 0.229 was the acceptable limit based on the current NGSP HbA1c standardization program monitoring criterion. To assess accuracy, each laboratorys results were compared to an NGSP Secondary Reference Laboratory (SRL9 using Tosoh G8) with ±6% bias considered acceptable.
Results: Methods included Roche Tina quant on Cobas Integra, Cobas 6000 and Hitachi 911, Sebia Minicap, and Axis-Shield NycoCard. One laboratory reported results as IFCC %HbA1c; these were aligned to NGSP using the NGSP/IFCC master equation (NGSP%=0.915(IFCC%)+2.15) for consistency of reporting. All laboratories except the two using the NycoCard showed acceptable precision and accuracy.
Conclusions: All but two participating T&T laboratories met acceptable criteria for HbA1c measurement. Since inaccurate HbA1c reporting negatively impacts diabetes care, we recommended that all laboratories report HbA1c in the same units and that only methods shown to report within acceptable limits of precision and accuracy be used. Continuous oversight of HbA1c testing is recommended.
20 - 22 Sep 2014
European Society for Paediatric Endocrinology