Glycated haemoglobin: what is the diagnostic yield at shortened testing intervals?

The proportion of sequential HbA1c exceeding critical difference (diagnostic yield), where it is considered clinically significant change, was calculated for different testing intervals. 12% and 26% of repeat HbA1c exceeded the critical difference before 30 and 90 days testing intervals, respectively. Repeating HbA1c within 4 weeks has poor diagnostic yield and should be avoided.