When is haemoglobin A1c inaccurate in assessing glycaemic control?

Many clinicians managing diabetics have encountered the problem of HbA1c values that do not agree with fingerstick glucose logs.

So, what are the situations in which HbA1c may be spuriously elevated or depressed? These issues are best understood after reviewing how HbA1c is defined and measured - topics fraught with considerable confusion.