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Leonid Kim MD - Is A1c the right test for you?

Thumbnail of the video “Leonid Kim MD - Is A1c the right test for you?”
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Author: Leonid Kim MD
Categories: Health Nutrition
Tags: health, nutrition
Views: 2 · Last viewed: 2026-10-16 15:00 UTC

Short Summary

Main recommendation: Don't rely on A1c alone if you have conditions or medications that distort it; use alternative tests such as fasting glucose, an oral glucose tolerance test, fructosamine, or, Dr. Leonid Kim's favorite, a continuous glucose monitor (CGM). Dr. Kim says A1c is still considered the gold standard for diagnosing and monitoring diabetes, but its results can be falsely high or low in several situations, and the pre-diabetes cutoff itself is debated across countries.

Key Points

  • A1c measures the percentage of hemoglobin in red blood cells coated with glucose, generally described as a 3-month average but correlating best with blood sugar from about 8 to 12 weeks earlier, and it doesn't reflect changes from the past month.
  • Iron deficiency, B12 or folate deficiency anemias, splenectomy, chronic alcohol use, and chronic salicylate (aspirin-type) use can falsely raise A1c.
  • Thalassemias, sickle cell anemia, enlarged spleen, and vitamin E at 600 mg or more per day can falsely lower A1c.
  • A1c can be unreliable in advanced kidney disease, after recent blood transfusions, and with vitamin C supplementation.
  • Diagnostic cutoffs differ: the US (CDC and American Diabetes Association) uses 5.7% for pre-diabetes, Canada and the UK use 6%, and the WHO does not endorse A1c for pre-diabetes diagnosis.

Details Worth Noting

  • Concrete instructions: If your A1c may be unreliable, ask your doctor about a fasting glucose test or an oral glucose tolerance test (blood glucose measured after a glucose challenge), or about fructosamine, which reflects roughly the past two to three weeks. GlycoMark (1,5-anhydroglucitol) is a less common test covering about one to two weeks. Dr. Kim says his favored option is a CGM, which provides real-time data on time in range, time in hypoglycemia, glucose variability, and high peak glucose levels.
  • A1c thresholds: 6.5% or higher is in the diabetes range, and 5.7% to 6.4% is in the pre-diabetes range, with 6.5% roughly corresponding to an average glucose of about 140.
  • Racial and ethnic differences: A1c is usually about 0.3 to 0.4 percentage points higher in African American, Hispanic American, and Asian American people than in white Americans with similar plasma glucose.
  • Fructosamine has its own limits, affected by severe liver disease or nephrotic kidney disease, since it depends on albumin levels.
  • CGM use is cost-dependent if not covered by insurance; it is indicated for all people with type 1 diabetes, and intermittent use is indicated for type 2 diabetes in those on intensive insulin, with hypoglycemia, or during major treatment changes; Dr. Kim notes there's growing evidence of CGM benefit in type 2 diabetes regardless of treatment regimen.

Bottom Line

A1c remains the standard diabetes test, but it can mislead in specific conditions, so people with those factors should confirm results with another test, and Dr. Kim's personal view is that he favors the more aggressive US screening approach but questions whether A1c alone adequately captures insulin resistance markers like glucose variability and post-meal glucose.