Can low 1,5-anhydroglucitol reflect recent post-meal glucose excursions?

Low serum 1,5-anhydroglucitol (1,5-AG; GlycoMark) is best understood as a marker of recent glycosuria and, consequently, of recent glucose excursions high enough to exceed the renal glucose threshold. It can complement HbA1c, which reflects longer-term average glycemia rather than short-term peaks.

Clinical evidence

• In a CGM study of people with type 1 or type 2 diabetes and HbA1c 6.5–8%, lower 1,5-AG correlated with greater glucose exposure above 180 mg/dL (r=−0.45; P=0.006). This supports its use as a directional indicator of recent clinically meaningful hyperglycemic excursions, often after meals.
• It is not a specific measure of post-meal peaks. A low value cannot identify the timing, frequency, or exact magnitude of excursions. In a 62-person OGTT study with HbA1c 5.6–6.5%, 1,5-AG alone poorly detected 1-hour glucose ≥180 mg/dL (AUC 0.543), although combining it with fasting glucose or HbA1c improved sensitivity.

Renal mechanism and interpretation

• 1,5-AG is freely filtered and normally almost completely reabsorbed in the proximal tubule. Luminal glucose competitively reduces this reabsorption—consistent with a principal role for renal SGLT5—thereby increasing urinary 1,5-AG loss and lowering serum concentrations.
• This mechanism is reinforced by randomized placebo-controlled empagliflozin data: pharmacologically induced glycosuria reduced serum 1,5-AG. Thus, SGLT2 inhibitors can make low 1,5-AG uninterpretable as evidence of post-meal hyperglycemia.

Clinical implications

• Renal function, renal glycosuria, impaired tubular handling, and SGLT2-inhibitor exposure should be considered before attributing a low result to glucose excursions; advanced CKD and dialysis can particularly complicate interpretation.
• Bottom line: The claim is supported: low 1,5-AG can reflect recent post-meal or other marked hyperglycemic excursions because urinary glucose promotes its renal loss, but it should be interpreted with CGM or glucose testing and medication/renal context rather than used alone.