Stability of Whole Blood at −70 °C for Measurement of Hemoglobin A1c in Healthy Individuals

To our knowledge, there are no significant published data on the long-term stability of stored whole blood for hemoglobin A1c (HbA1c) analysis Stored hemolysates (1) and buffy coat samples (2) can provide reliable estimates of HbA1 and HbA1c, respectively; in large epidemiologic studies, however, storage of whole blood would be more practical. A recent report stated that whole blood was stable at −70 °C for 1 year, but no evidence was cited (3). The aim of this study was therefore to test the hypothesis that whole blood is stable at −70 °C for 1 year for HbA1c measurement. Venous blood was collected from 99 children (age, 10 years) without diabetes over a 3-week period in the Avon Longitudinal Study of Parents and Children (ALSPAC; www.alspac.bris.ac.uk). The anticoagulant used was lithium heparin. Available blood was limited, and 10 identical 5-μL aliquots of whole blood in 1 mL of 40H-HPLC-hemolysant (specific to our assay; contains phosphate buffer, sodium azide, and surfactant) were prepared for each child. One aliquot was assayed fresh for HbA1c (baseline values), and the remainder were frozen at −70 °C. Whole blood was also stored undiluted in hemolysant. Stored aliquots were assayed for HbA1c after periods of 9, 16, 25, 31, 45, and 56 weeks. After 56 weeks, the stored undiluted whole blood from each child was also assayed. HbA1c was measured with the HA-8140 Hi-Auto HbA1c analyzer (Menarini Diagnostics) maintained in alignment with the Diabetes Control and Complications Trial method. Imprecision (CV) was stable at 1.8% (mean HbA1c, 5.5%) throughout the study.