Why Your HbA1c and Your Meter Disagree

It is common for an HbA1c result to look worse — or better — than the readings on your meter suggest it should. Sometimes that gap is real, and sometimes the test itself is being distorted.

HbA1c measures how much glucose is stuck to the haemoglobin in your red blood cells, which reflects roughly three months of average glucose. Below 5.7% is normal, 5.7 to 6.4% is prediabetes, and 6.5% or above indicates diabetes. The lab may also report an estimated average glucose (eAG) in mg/dL, converted from that percentage.

Ordinary reasons for a gap

• You test at the times that look good. Mostly-fasting testing misses post-meal peaks that HbA1c still counts.
• eAG is an average, not a day. It will rarely match any individual reading.
• Your last three weeks weigh more than the three months before them.

Medical reasons the test can mislead

This is the part that matters in India, and it is under-discussed. HbA1c is unreliable when anything changes the life or type of your red blood cells:

• Haemoglobin variants, which are more common in people of Southeast Asian, African and Mediterranean descent, can push the result falsely high or low depending on the method used.
• Iron-deficiency anaemia falsely raises HbA1c.
• Kidney failure or liver disease can produce false results.
• Recent blood loss, a transfusion, dialysis or sickle cell disease all change it.
• Pregnancy, where a three-month average may include weeks before conception.

If your meter and your report disagree persistently, that is worth raising rather than dismissing — a different A1C method, or a different test altogether, may be needed.