15-Anhydroglucitol (15-AG) Biomarker Testing
It measures recent high-glucose excursions over ~1–2 weeks and complements A1c; order through Vitals Vault with Quest collection and PocketMD support.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
15‑Anhydroglucitol (15‑AG) is a blood test that helps estimate whether you have had meaningful glucose spikes in the last week or two. It is often used as a “between A1c checks” marker, especially when you want more insight than a single fasting glucose number.
Unlike A1c, which reflects average glucose over roughly 2–3 months, 15‑AG tends to drop when your blood glucose rises high enough that glucose spills into your urine. That makes it particularly useful for spotting frequent post‑meal highs or short-term loss of control.
Your result is most helpful when you interpret it alongside your medications, kidney health, and other glucose markers. If you are using continuous glucose monitoring (CGM), 15‑AG can also serve as a lab-based cross-check of recent patterns.
Do I need a 15‑Anhydroglucitol (15‑AG) test?
You might consider a 15‑AG test if your A1c looks “okay,” but you still suspect you are having significant glucose spikes after meals. This can happen when fasting glucose is near normal while post‑prandial (after eating) glucose runs high, or when your day-to-day glucose swings are wide.
This test can also be useful if you recently changed your nutrition plan, started or adjusted diabetes medications, or want a short-term checkpoint before your next A1c is due. Because 15‑AG responds over about 1–2 weeks, it can give you feedback sooner than A1c.
You may not need 15‑AG if you already have clear, consistent CGM data and your clinician is satisfied with time-in-range and variability metrics, or if your kidney function is significantly reduced (which can make interpretation less reliable). Testing supports clinician-directed care and shared decision-making; it does not diagnose diabetes by itself.
15‑AG is measured on CLIA-certified laboratory platforms; results should be interpreted in clinical context and are not a standalone diagnosis.
Lab testing
Order a 15‑AG test to check for recent glucose spikes
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
With Vitals Vault, you can order a 15‑AG lab test without needing to coordinate a separate referral, then complete your blood draw at a participating Quest collection site. Your report is delivered in a clear format so you can compare results over time.
If you want help understanding what your number suggests about recent glucose spikes, PocketMD can walk you through common patterns, medication-related caveats (including diabetes drugs that affect urine glucose), and which companion labs to consider for a fuller picture.
Many people use 15‑AG as a targeted add-on when they are troubleshooting post-meal highs, checking whether a new plan is working, or deciding whether to broaden testing to include A1c, fasting insulin, or kidney markers that influence interpretation.
- Order online and draw at Quest locations
- Results you can trend over time in one place
- PocketMD guidance for next-step questions to bring to your clinician
Key benefits of 15‑AG testing
- Gives a short-term view (about 1–2 weeks) of meaningful glucose excursions that A1c can miss.
- Helps flag frequent post-meal highs even when fasting glucose looks acceptable.
- Supports medication or lifestyle change check-ins without waiting months for A1c to move.
- Adds context when symptoms (thirst, urination, fatigue) don’t match your current A1c.
- Can complement CGM by providing a standardized lab marker of recent hyperglycemia exposure.
- Helps you and your clinician decide whether to intensify monitoring or broaden metabolic testing.
- Useful for retesting and trend tracking when interpreted alongside kidney function and medication use.
What is 15‑Anhydroglucitol (15‑AG)?
15‑Anhydroglucitol (15‑AG) is a naturally occurring sugar-like molecule that circulates in your blood. Under typical conditions, your kidneys filter it and then reabsorb most of it back into the bloodstream, so blood levels stay relatively steady.
When your blood glucose rises high enough to exceed the kidney’s reabsorption capacity for glucose (often called the “renal threshold”), glucose spills into the urine. In that situation, glucose competes with 15‑AG for reabsorption, and more 15‑AG is lost in urine. The result is that your blood 15‑AG level tends to fall when you have repeated or sustained hyperglycemic spikes.
Because this mechanism is tied to glucose spilling into urine, 15‑AG is best thought of as a marker of recent significant highs rather than a marker of average glucose. It is most informative when you pair it with A1c and/or glucose monitoring data.
What time window does it reflect?
15‑AG generally reflects glycemic exposure over roughly the prior 7–14 days, although the exact window varies by your baseline level, diet, and how often glucose exceeds the renal threshold. It tends to respond faster than A1c, which is why it is sometimes described as an “intermediate” glycemic control marker.
How is it different from A1c and fructosamine?
A1c estimates average glucose over ~2–3 months and can look normal even if you have big post-meal spikes. Fructosamine and glycated albumin reflect shorter averages (about 2–3 weeks) but still represent an average. 15‑AG is more specifically sensitive to higher peaks that trigger urinary glucose loss, so it can highlight a pattern that averages smooth over.
What do my 15‑AG results mean?
Low 15‑AG (often suggests recent glucose spikes)
A lower 15‑AG level commonly means you have had more frequent or more pronounced hyperglycemic excursions in the last week or two, especially after meals. It can be a clue that your A1c is underestimating day-to-day highs, or that recent control has worsened since your last A1c. If your result is low, it is worth reviewing meal patterns, medication timing, and any recent illness or steroid use that can push glucose higher.
In-range 15‑AG (often suggests fewer significant excursions)
An in-range or higher 15‑AG level generally suggests you have had fewer episodes where glucose rose high enough to spill into urine recently. This is reassuring when it matches your CGM or fingerstick data and your A1c goals. If you still feel symptoms that you associate with glucose swings, your clinician may look at other explanations (sleep, thyroid, anemia, medications) or use CGM to check for lows and highs that 15‑AG may not capture.
High 15‑AG (usually not a problem by itself)
Higher 15‑AG levels typically indicate that you have not been losing much 15‑AG in urine, which often aligns with fewer significant hyperglycemic spikes. A “high” value is usually not treated as harmful on its own. The key is whether it fits with your overall metabolic picture, including A1c, fasting glucose, and your symptoms.
Factors that can influence 15‑AG
Kidney function matters because 15‑AG depends on filtration and reabsorption; reduced kidney function can make results harder to interpret. Medications that increase urinary glucose (especially SGLT2 inhibitors) can lower 15‑AG even if your overall control is improving, so your medication list is essential context. Diet patterns and recent rapid changes in glucose control can shift 15‑AG over days to weeks. Hydration status and acute illness can also indirectly affect glucose patterns and urinary losses.
What’s included
- 1,5 Ag, Intermediate Glycemic Control
Frequently Asked Questions
What is a normal 15‑AG level?
“Normal” depends on the lab method and reference interval on your report, so use the range printed next to your result. In general, higher 15‑AG tends to mean fewer recent glucose excursions above the renal threshold, while lower values suggest more frequent significant spikes. If you are on an SGLT2 inhibitor or have reduced kidney function, ask your clinician how that changes interpretation.
Do I need to fast for a 15‑AG blood test?
Fasting is not always required for 15‑AG, but many people combine it with fasting glucose, insulin, or lipid testing, which may require fasting. Follow the instructions provided with your order, and keep your usual routine unless your clinician advises otherwise. Consistency helps when you plan to retest and trend results.
How is 15‑AG different from A1c?
A1c reflects average glucose over roughly 2–3 months, so it can look acceptable even if you have frequent post-meal highs. 15‑AG responds over about 1–2 weeks and tends to drop when glucose spikes are high enough to cause glucose in the urine. Many clinicians use 15‑AG as a complement to A1c when they suspect glycemic variability or postprandial hyperglycemia.
Can SGLT2 inhibitors affect 15‑AG results?
Yes. SGLT2 inhibitors intentionally increase urinary glucose excretion, which can lower 15‑AG independent of whether your overall glucose control is improving. If you take an SGLT2 inhibitor, your 15‑AG may look “low” even with better A1c or CGM metrics, so interpretation should be medication-aware.
How often should I retest 15‑AG?
Because 15‑AG reflects roughly the prior 1–2 weeks, retesting is often considered a few weeks after a meaningful change, such as a medication adjustment or a new nutrition plan. Your clinician may time retesting based on your goals and whether you are also tracking A1c or CGM data. If you are trending results, try to keep testing conditions similar each time.
What other tests go well with 15‑AG?
Common companion tests include A1c, fasting glucose, and sometimes fasting insulin to better understand insulin resistance. Kidney function markers (such as creatinine and estimated GFR) can be important because renal handling affects 15‑AG. If there is concern for anemia or altered red blood cell turnover (which can distort A1c), your clinician may also consider a complete blood count or alternative glycemic markers.