Monitoring Analytical Quality in Routine Glycohemoglobin Measurements

Abstract

Maintenance of hemoglobin (Hb)A1c (a specific glycohemoglobin) at <7% has been recommended for effective treatment of both type 1 and type 2 diabetes (1)(2)(3)(4)(5). Because a higher frequency of HbA1c testing may lead to superior glycemic control (6), it can be anticipated that an increased number of HbA1c assays will be performed and increased attention will be given to analytical standardization (7)(8). HbA1c assays based on different methods are available (1), but most laboratories in Italy (e.g., 164 of 201 participants in a quality assessment scheme during the year 2001) use HPLC. Several HPLC instruments for measuring HbA1c have been evaluated recently (9)(10)(11)(12). We report our experience to demonstrate how use of routine internal quality control and participation in external quality assessment schemes (EQAS), with occasional method comparison exercises, may provide information that laboratory performance is being kept within acceptable limits. Leftover EDTA-blood samples, stored at 4 °C and assayed within 3 days, were used in this study for method comparison exercises. Internal quality-control (QC) samples were prepared as follows (13)(14): samples with either low or high HbA1c were hemolyzed by shaking one volume of saline-washed erythrocytes with one volume of water and one volume of carbon tetrachloride and were pooled to yield “low” and “high” QC pools (mean HbA1c, 5.07% and 12.7%, respectively). The pools were stored in 0.5-mL aliquots at −80 °C. Lyophilized QC materials from Bio-Rad (Lyphochek Diabetes Control, Levels 1 and 2; mean HbA1c, 5.14% and 9.84%, respectively) were also used. Both the frozen and the reconstituted lyophilized QC materials, properly identified, were introduced in the analyzer after being diluted 1:201 (5 μL of QC material plus …