Posted by Sten Westgard, MS
Glycated hemoglobin is becoming a hotter topic in medical laboratories. Not only is there a movement to use this test as a way to diagnosis diabetes, but there is also increasing scrutiny of assay performance by National Glycohemoglobin Standardization Program (NGSP).
While NGSP is tightening the requirements for performance, the use of the test seems to be outpacing the performance of the assays. A recent letter to the editor highlights this issue:
Glycated haemoglobin A1c (HbA1c) in the diagnosis of diabetes mellitus: don't forget the performance of the HbA1c assay, RK Schindheim, E Lenters-Westra and RJ Slingerland, Diabet Med. 27, 1214-1215 (2010)
Some excerpts of that letter:
"...healthcare professionals should be aware of the inherent analytical variability of the HbA1c laboratory assays. Although the analytical performance has improved over the last 5 years, all methods still do not concur with the primary reference methods, which may contribute to bias in epidemiological studies and lead to misclassification of patients in the diagnosis of diabetes mellitus. Indeeed, the results of the College of American Pathologists 2009 GH2-B Survey Data on HbA1c...demonstrated that only two of 25 methods have an inter-laboratory coefficient of variation of <2% with the sample with a reference value of 6.6%....the analytical bias ranged from -0.19 to 0.27% HbA1c....
"The clinical biochemist can play a valuable role in this matter and should be encouraged to use HbA1c methods with optimal analytical performance (no bias and a total coefficient of variation of <2%). Given the insufficient analytical performance of most HbA1c point-of-care testing devices, caution should be exercised when applying these devices in the diagnosis of diabetes mellitus."
A short article with an important point. The potential of the HbA1c assay is great, but only if we assure that we've got the quality we need first.
I agree that, overall, HbA1c assays still need to be improved. However, we should also keep in mind that the CV that is mentioned is a between-laboratory CV. The within-lab CVs are likely to be quite a bit lower. The overall CV for all methods/labs combined was <=4% at all HbA1c levels in the most recent 2010B survey. Our goal is <3.5%. Also, over 90% of labs were within ±7% (pass/fail criterion for 2011)of the assigned value at all HbA1c levels. We hope to see this pass rate increase as well.
Posted by: Randie Little | February 08, 2011 at 11:29 AM