1,5-Anhydroglucitol (1,5-AG), Intermediate Glycemic Control
The 1,5-anhydroglucitol test measures a dietary polyol whose serum level falls when glucose exceeds the renal threshold, providing a one- to two-week window into glycaemic control. It is particularly sensitive to postprandial hyperglycaemic excursions and variability, complementing HbA1c in diabetes management but limited by renal impairment and SGLT2 inhibitor use.
1
Biomarkers
Blood (serum)
Sample
3–5 business days
Turnaround
No
Fasting
What is the 1,5-AG test?
The 1,5-Anhydroglucitol test measures a dietary polyol whose serum concentration falls when glucose exceeds the renal threshold, offering a window into intermediate-term glycaemic control — specifically the one to two weeks before the blood draw. Unlike HbA1c, which averages control over three months and is weighted toward fasting and pre-meal glucose, 1,5-AG is exquisitely sensitive to postprandial spikes and short-term variability, dropping within days of hyperglycaemic excursions and recovering slowly once control improves. Practitioners order 1,5-AG when they suspect that HbA1c is masking clinically important glycaemic lability — for instance, a patient whose HbA1c is near target but who reports symptoms of hyperglycaemia, or when adjusting rapid-acting insulin or newer agents and needing feedback faster than HbA1c can provide. It is not a replacement for HbA1c or continuous glucose monitoring but a complementary tool in the metabolic-diabetes toolkit, particularly valuable in type 1 diabetes, brittle type 2 diabetes, and gestational diabetes where postprandial control matters most.
What does the 1,5-AG test measure?
1,5-Anhydroglucitol is a dietary polyol structurally similar to glucose, absorbed from food and maintained at relatively constant plasma concentrations through glomerular filtration and near-complete tubular reabsorption. When plasma glucose exceeds the renal threshold (approximately 10 mmol/L or 180 mg/dL), glucose competes with 1,5-AG for reabsorption in the proximal tubule, leading to urinary loss of 1,5-AG. Because 1,5-AG has a circulating half-life of several days and dietary intake is steady, its serum concentration inversely reflects the frequency and severity of postprandial or intermittent hyperglycaemia over the preceding one to two weeks.
1,5-AG fills a temporal gap between day-to-day capillary glucose monitoring and the three-month average provided by HbA1c. It is particularly sensitive to postprandial glucose spikes and short-term glycaemic variability, making it useful for detecting masked hyperglycaemia in patients whose HbA1c appears acceptable but who experience frequent excursions above the renal threshold. The marker is less informative in advanced renal impairment, where tubular handling is altered, and does not replace HbA1c or glucose monitoring but complements them in selected cases.
Why is the 1,5-AG test ordered?
- Monitoring of patients with type 1 diabetes whose HbA1c appears acceptable but who report unexplained symptoms or have concerns about postprandial excursions
- Assessment of short-term glycaemic variability in type 2 diabetes during titration of prandial insulin or newer agents such as GLP-1 receptor agonists
- Detection of masked postprandial hyperglycaemia in patients with near-target HbA1c whose fasting glucose is well controlled but postprandial values are suspected to be elevated
- Evaluation of intermediate-term glycaemic control in gestational diabetes, where rapid feedback on dietary or insulin adjustments is clinically useful
- Investigation of hypoglycaemia risk in patients with brittle diabetes, where 1,5-AG can help identify periods of both hyper- and hypoglycaemia when interpreted with glucose logs
- Short-interval reassessment of glycaemic control following therapeutic changes, when waiting three months for HbA1c is impractical
- Situations where HbA1c interpretation is confounded by haemoglobinopathy, recent transfusion, or haemolysis, though 1,5-AG itself has renal limitations
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
3–5 business days
Collection notes
Phlebotomy at a Quest Diagnostics patient service centre; no special preparation required. Note any use of SGLT2 inhibitors or significant renal impairment on the requisition, as these limit interpretability.
Specimen requirements
Minimum 0.5 mL serum. Separate from cells promptly; stable refrigerated for up to one week. Ensure the specimen is not haemolysed.
What can affect 1,5-AG results?
Impaired glomerular filtration and altered tubular reabsorption disrupt the normal relationship between glucose excursions and 1,5-AG loss, rendering the marker unreliable in moderate to severe renal impairment.
Dietary load can transiently raise serum 1,5-AG independently of glycaemic control, though the effect is usually modest in Western diets; very high intake may mask hyperglycaemic excursions.
Any condition that lowers the renal threshold for glucose or increases urinary glucose loss will drive down 1,5-AG by the same competitive mechanism, confounding interpretation; SGLT2 inhibitors render 1,5-AG uninterpretable.
Sustained glucose above the renal threshold during acute illness rapidly depletes 1,5-AG; the marker reflects the excursion but recovery lags clinical improvement by several days.
Heavy alcohol intake may alter hepatic and renal handling of polyols, though the clinical significance for 1,5-AG interpretation is minor compared with other factors.
What do 1,5-AG results mean?
Elevated
High 1,5-AG (≥14 µg/mL) reflects good short-term glycaemic control with few excursions above the renal threshold. In the context of a concordant HbA1c, this is reassuring; if HbA1c is elevated but 1,5-AG is high, consider that the HbA1c may be driven by chronic mild hyperglycaemia rather than acute spikes, or that control has recently improved.
Normal
A 1,5-AG in the 10–14 µg/mL range suggests moderate glycaemic control with occasional excursions. Interpret in the clinical context — if symptoms or HbA1c suggest suboptimal control, the intermediate 1,5-AG supports the need for adjustment; if both are reassuring, the patient is likely stable.
Reduced
Low 1,5-AG (<10 µg/mL) indicates frequent or severe hyperglycaemic excursions over the preceding one to two weeks. Common causes include inadequate prandial insulin coverage, dietary indiscretion, intercurrent illness, or use of SGLT2 inhibitors. Cross-check with glucose logs, HbA1c, and medication history; if SGLT2 inhibitors are in use, 1,5-AG is not interpretable.
Note: 1,5-AG is unreliable in chronic kidney disease (eGFR <60), in patients taking SGLT2 inhibitors, and in conditions with primary renal glycosuria. It does not replace HbA1c or glucose monitoring but offers a unique one- to two-week snapshot of glycaemic variability. Serial measurement is more informative than a single value, and trends should be interpreted alongside the full clinical and laboratory picture.
Frequently asked questions
HbA1c averages glycaemic control over three months and is weighted toward fasting and pre-meal glucose, while 1,5-AG reflects the preceding one to two weeks and is highly sensitive to postprandial spikes and short-term variability. The two markers are complementary rather than interchangeable.
How to access the 1,5-AG test
The 1,5-AG reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Dungan KM. 1,5-Anhydroglucitol (GlycoMark) as a marker of short-term glycemic control and glycemic excursions. Expert Rev Mol Diagn. (2008)
- American Diabetes Association Standards of Medical Care in Diabetes—2023. Diabetes Care. (2023)
- Kim WJ, Park CY. 1,5-Anhydroglucitol in diabetes mellitus. Endocrine. (2013)
- Yamanouchi T, Akanuma Y. Serum 1,5-anhydroglucitol (1,5 AG): new clinical marker for glycemic control. Diabetes Res Clin Pract. (1994)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.