INTERLABORATORY VARIATION OF GHB ASSAYS IN VICTORIA, AUSTRALIA

OBJECTIVE - To determine the extent of interlaboratory variation and a ccuracy in the measurement of glycated hemoglobin (GHb). RESEARCH DESI GN AND METHODS - All laboratories that measure glycated hemoglobin in the Stare of Victoria, Australia, were invited to participate, and pos itive responses were received from 27 of 30 laboratories. An aliquot o f blood drawn from three patients with diabetes and varied glycemia an d from one nondiabetic subject was sent to each participating laborato ry. Distribution of results was analyzed according to the reported res ults and their variance from an assigned reference value and were expr essed as differing from this latter value as percentage bias and in ab solute terms. A bias greater than or equal to 10% or an absolute diffe rence of greater than or equal to 1% HbA(1c) from the reference value was considered significant, RESULTS - Reported results for the same bl ood sample ranged from 4.1 to 5.8%, 5.1 to 8.2%, 6.7 to 9.3%, and 10.1 to 14.7% for the specimens from the nondiabetic subject and the diabe tic patients with good, moderate, and poor glycemic control, respectiv ely. The proportion of laboratories with results that differed by grea ter than or equal to 10% bias from the reference value were 39% (It of 30), 29% (9 of 30), 16% (5 of 30), and 32% (10 of 30), and the propor tion reporting results that differed by greater than or equal to 1% Hb A(1c) in absolute terms from the reference values were 3% (1 of 30), 6 % (2 of 30), 16% (5 of 30), and 23% (7 of 30) for the specimens from t he nondiabetic subject and the diabetic patients with good, moderate, and poor glycemic control, respectively. CONCLUSIONS - A substantial d egree of interlaboratory variation for GHb measurement exists in Victo ria, Australia. This may lead to difficulties in interpretation when G Hb is assayed by different laboratories in the same patient over time. Interlaboratory standardization may be achievable by calibration to a standard assigned by a reference laboratory and distributed to all la boratories measuring GHb.