Why can HbA1c be unreliable in some patients, and what alternative measures can be used?

• A. HbA1c is unreliable in conditions affecting red cell turnover (anemia, hemoglobin variants, recent transfusion); alternatives include fructosamine, glycated albumin, or serial plasma glucose measurements.
• B. HbA1c is always reliable regardless of red cell turnover.
• C. Glycated Hb variants do not affect HbA1c interpretation.
• D. Only fasting plasma glucose is an acceptable alternative.

Answer: (A)

HbA1c depends on how long red blood cells circulate in the bloodstream. If red cell turnover is changed—such as in anemia, hemolysis, recent transfusion, or other conditions that shorten or lengthen RBC lifespan—the amount of glucose actually bound to hemoglobin can be misrepresented, making HbA1c readings unreliable. Hemoglobin variants can also interfere with some HbA1c measurement methods, leading to inaccurate results regardless of true average glucose levels. Because of these factors, HbA1c may not accurately reflect glycemic control in these patients.

Alternatives like fructosamine or glycated albumin come into play because they measure glycation of serum proteins rather than hemoglobin. Serum proteins turn over much more quickly (roughly a couple of weeks), so these tests reflect shorter-term glycemic exposure and are less affected by RBC lifespans or transfusions. Serial plasma glucose measurements, including multiple readings over days to weeks or the use of continuous glucose monitoring, provide a direct assessment of glucose levels over time without relying on the lifespan of red cells or the presence of Hb variants.

So, when HbA1c reliability is in question, using fructosamine, glycated albumin, or repeated plasma glucose measurements offers a practical and informative alternative.