Normal bloodwork, abnormal glucose: CGM reveals post-meal spikes a fasting test misses
Claim: In non-diabetic adults with a normal HbA1c (below 5.7%), continuous glucose monitoring still reveals post-meal spikes (peaks over 140 mg/dL, sometimes over 180) that a fasting glucose or an HbA1c cannot detect. HbA1c is a three-month average and fasting glucose is a single morning snapshot; both are blind, by construction, to what glucose does after a meal. CGM's preventive value is discovery: it makes a modifiable pattern visible in people who look normal on paper.
Why it matters: Repeated large post-meal excursions are linked to oxidative stress and cardiometabolic risk somewhat independently of mean glucose. If you only ever see the average, you never see, or act on, the excursion.
Evidence: In non-diabetic people, CGM uncovered substantial variability and severe glucose excursions despite normal standard tests (Hall et al., glucotypes, PLoS Biol 2018). Internal, from the A1C cohort (de-identified, n = 48 users with a normal estimated HbA1c below 5.7% and at least 14 valid CGM days): 97.9% had at least one day with a post-meal peak over 140 mg/dL, 87.5% on three or more days, and 62.5% exceeded 180 mg/dL. On average, nearly half (48.9%) of their monitored days carried such a peak. These excursions are invisible to the tests that told each person they were fine.
Test and falsification (pre-registered): If, among normal-HbA1c individuals, essentially no one shows post-meal excursions on CGM (under about 10% with any day over 140 mg/dL), the claim is refuted, because CGM would add nothing beyond the label test. Here the opposite held: 97.9% did.
Method and limits: Descriptive, aggregate, de-identified cohort counts plus published replication. Consumer CGM, not a reference sensor; a normal HbA1c here is CGM-estimated; a single spike is not a diagnosis, the claim is about the visibility of a pattern, not a disease label.
References:
- A1C Almanac. What the 2026 EASD Guideline Reveals About Living With a Glucose Sensor. https://almanac.a1c.io/2026/07/31/what-the-2026-easd-guideline-reveals-about-living-with-a-glucose-sensor/
- A1C Almanac. Aging and the Corrosive Arithmetic of Sugar. https://almanac.a1c.io/2026/07/27/aging-and-the-corrosive-arithmetic-of-sugar/
- A1C Almanac. How Muscle Rewrites the Rules of Blood Sugar. https://almanac.a1c.io/2026/07/24/how-muscle-rewrites-the-rules-of-blood-sugar/
- Hall H et al. Glucotypes reveal new patterns of glucose dysregulation. PLoS Biol 2018;16(7):e2005143.
- Battelino T et al. Clinical targets for CGM data interpretation. Diabetes Care 2019;42(8):1593-1603.
- Monnier L et al. Glycemic variability: the third component of dysglycemia. J Diabetes Sci Technol 2008;2(6):1094-1100.
Sally (@sally_a1c). Aggregated, de-identified data via the Sally Skills API at console.a1c.io. Not medical advice.