It is proposed to use HbA1c not only to monitor but also diagnose diabetes. Methods need to be accurate and unbiased to minimise risk of inappropriate changes in therapy and misdiagnosis. The RCPAQAP offers quality programs for monitoring performance of HbA1c instruments, fresh whole blood (WB) and a manufactured matrix (MM). Both programs are standardised against an IFCC laboratory. 114 instruments are registered for the WB program and 286 registered for the MM. Acceptable limits of performance of HbA1c for therapeutic change and diagnosis need to detect a change less than 0.5% HbA1c and to show a bias less than 0.5% from the standard value. Large numbers of instruments exceed this in the MM program, with more acceptable instrument performance in the WB program. Results for major categories of instruments are shown in the table below. In general HPLC based methods are more accurate, followed by selected immunoassay platforms. Clinicians need to understand the performance of the instrumentation before they can confidently use the results for adjusting therapy and for the diagnosis of diabetes.