GlycoMark

Your A1c can sit in a comfortable range while your blood sugar still surges after meals. Those after-meal spikes can drive vascular and nerve damage, but a single fasting glucose or quarterly A1c often misses them entirely.

GlycoMark (1,5-anhydroglucitol, or 1,5-AG) helps fill that gap. It captures the last one to two weeks of glucose surges that pushed your blood sugar above the kidney's spill threshold of roughly 160 to 180 mg/dL, giving you a window into glycemic patterns that long-term averages flatten out.

What This Test Actually Measures

1,5-AG (1,5-anhydroglucitol) is a sugar that comes from food and stays at a steady level in your blood when glucose is well controlled. Your kidneys normally reabsorb it back into circulation. When blood glucose climbs above the kidney spill point, glucose competes with 1,5-AG for that reabsorption pathway, so 1,5-AG gets dumped into urine and serum levels fall. The bigger and more frequent your glucose spikes over the past one to two weeks, the lower your 1,5-AG.

That makes the number a mirror image of recent high blood sugar. A high 1,5-AG suggests few or no glucose excursions above the kidney threshold. A low number means your blood sugar has been crossing that threshold often, even if your fasting glucose and A1c look acceptable.

Why It Matters: Hidden Spikes Despite a Good A1c

In a study of 100 adults with type 2 diabetes who had reached an A1c target of 7.5% or below, 1,5-AG values were widely dispersed. Many of these people, considered well controlled by standard metrics, still had low 1,5-AG values consistent with significant post-meal glucose excursions. The finding shows how A1c can mask the day-to-day spikes that drive complications.

In a U.S. trial of 77 adults with diabetes starting or adjusting therapy, 1,5-AG and fructosamine improved by week 2 of treatment changes, while A1c only changed significantly by week 4. If you adjust your diet, start a new medication, or change your routine, 1,5-AG sees the difference faster.

Mortality and Cardiovascular Risk

In a real-world cohort of 3,721 adults with type 2 diabetes, lower serum 1,5-AG was linked to higher all-cause and cardiovascular death over follow-up. The relationship was roughly linear, meaning that as 1,5-AG dropped, mortality risk climbed steadily.

What this means for you: a low 1,5-AG is not just a number. It signals the type of glucose pattern (frequent spikes above 160 to 180 mg/dL) that can quietly damage arteries and organs, and that pattern carries real long-term consequences.

Microvascular Disease and Eye Risk

In the ADVANCE trial of 7,510 adults with type 2 diabetes, intensive glucose-lowering therapy raised 1,5-AG levels, and higher 1,5-AG tracked with lower risk of microvascular events such as kidney and eye complications. The signal was clearest for microvascular disease rather than heart attacks or stroke.

Diabetic retinopathy research adds another layer. Even among people with high time-in-range on continuous glucose monitoring, those with lower 1,5-AG still had higher retinopathy risk, suggesting the marker captures a slice of glucose exposure that other tools miss.

Beta Cell Mass: A Newer Use

Beyond glucose excursions, 1,5-AG appears to track beta cell mass, the insulin-producing cells in your pancreas. In one human study, circulating 1,5-AG fell by roughly 50% after partial pancreatic surgery, mirroring the loss of beta cells, even when glucose tolerance varied. This emerging finding is exploratory but suggests the marker may eventually help flag pancreatic reserve in people at risk for diabetes.

Reference Ranges

The ranges below come from a U.S. community study of 1,799 adults without known diabetes, used to derive cutpoints that correspond to standard high-blood-sugar thresholds. They are orientation, not universal targets, and your lab may report different values.

Source: Selvin et al., Clinical Chemistry, 2018. Cutoff studies in Asian populations have proposed alternative thresholds (for example 13.3 µg/mL or 15.9 µg/mL) and reference intervals can vary by sex and age, so compare your results within the same lab over time for the most meaningful trend.

When Results Can Be Misleading

• SGLT2 inhibitors: drugs like canagliflozin, empagliflozin, and dapagliflozin force glucose out through the urine continuously. In a study of 291 patients on these drugs, most had very low 1,5-AG (around 2 µg/mL or less) regardless of how well their blood sugar was controlled. The number drops because the drug causes constant urinary glucose loss, not because your glucose is spiking. The test is not interpretable in the usual way while you are on these medications.
• Advanced kidney disease: in mild to moderate kidney impairment (CKD stages 1 to 3), 1,5-AG remains a reliable glucose marker. In stages 4 to 5, the kidney's handling of glucose changes enough that the test loses validity.
• Pregnancy and rare genetic conditions: pregnancy alters the kidney's glucose threshold, and certain genetic forms of diabetes (such as HNF-1α MODY) shift 1,5-AG independently of average glucose. Interpret cautiously in these settings.
• Recent dietary changes: in the OmniCarb randomized trial of 159 adults without diabetes, lowering both glycemic index and carbohydrate proportion reduced 1,5-AG levels even in people without high blood sugar, suggesting carbohydrate intake itself contributes to baseline values.

Tracking Your Trend

A single 1,5-AG reading is a snapshot of the last one to two weeks. Its real value comes from repeat testing, because the marker responds quickly to changes in your routine, medication, or diet. Improvements show up within two weeks, far faster than A1c.

A practical cadence: get a baseline now, retest in 4 to 8 weeks if you are making changes (new medication, dietary shift, weight loss), and then every 3 to 6 months alongside your A1c. If your A1c is stable but your 1,5-AG drops, that is an early signal of new spikes that A1c will eventually catch up to.

What to Do If Your Result Is Low

A low 1,5-AG with a normal A1c suggests post-meal glucose surges that standard testing missed. The next step is to confirm what is happening after meals. Order or repeat the following alongside 1,5-AG:

• Fasting glucose and A1c: establish your average glucose context.
• Continuous glucose monitor (CGM) for 10 to 14 days: captures the actual size and timing of post-meal spikes.
• Fasting insulin and HOMA-IR: identify insulin resistance driving the excursions.
• Glycated albumin or fructosamine: complementary short-term markers that confirm short-term glucose patterns.

If the pattern is confirmed, an endocrinologist or experienced primary care physician can help you target the spikes with diet timing, exercise after meals, or medication adjustments. A low 1,5-AG with no other abnormalities can still be meaningful: it is sometimes the earliest lab signal that glucose regulation is slipping.