- βIf you take an SGLT2 inhibitor like Jardiance or Farxiga, your A1C may appear worse than your actual blood sugar control β and CGM data may tell a more accurate story.
| Country | Japan |
| Institution | Nagoya University Graduate School of Medicine |
| Journal | Journal of diabetes investigation |
| Year | 2026 |
| PMID | 41235449 |
Japanese Research Reveals A1C May Be Misleading for a Common Class of Diabetes Drugs
A study from Japan published in the Journal of Diabetes Investigation suggests that patients taking SGLT2 inhibitor medications β one of the most popular classes of diabetes drugs in the US β may have A1C readings that overestimate how poorly their blood sugar is actually controlled.
What Are SGLT2 Inhibitors?
SGLT2 inhibitors (brand names include Jardiance, Farxiga, and Invokana) work by causing the kidneys to flush excess sugar out through urine rather than returning it to the bloodstream. They are widely prescribed in both Japan and the US for type 2 diabetes, and are also valued for their heart and kidney protective benefits.
What Did the Study Find?
Researchers at Nagoya University Graduate School of Medicine compared two measures of blood sugar control in 136 diabetes patients:
- HbA1c (A1C): The standard 3-month blood sugar average used in most US doctor's offices
- Glucose Management Indicator (GMI): An estimated A1C equivalent calculated from continuous glucose monitor (CGM) data β reflecting real-time glucose averages
After carefully adjusting for other influencing factors, the team found that patients on SGLT2 inhibitors showed a statistically significant gap between their A1C and their GMI β with A1C running approximately 0.42 percentage points higher than what their CGM data suggested. In other words, their lab-reported A1C looked worse than their actual day-to-day blood sugar control.
Why Does This Happen?
The researchers point to a known biological effect: SGLT2 inhibitors may alter red blood cell lifespan or increase the proportion of older red blood cells, which can artificially elevate A1C readings β even when real glucose levels are well managed. This has been observed in earlier research but rarely studied against CGM-based estimates so directly.
How Does This Compare to US Guidelines?
Current American Diabetes Association (ADA) guidelines primarily rely on A1C to assess long-term glucose control, with a general target below 7% for most adults. This Japanese study raises an important caution: for patients on SGLT2 inhibitors, A1C alone may not be a fully reliable picture. The ADA does acknowledge that CGM metrics, including GMI, can complement A1C β and this research reinforces that recommendation, particularly for this drug class.
Why This Matters for US Patients
Millions of Americans currently take SGLT2 inhibitors, and many may be having treatment adjusted β or feeling anxious β based on A1C numbers that don't reflect their true glucose management. If your doctor uses A1C as the primary measure of your control and you're on one of these medications, it may be worth asking whether CGM data or additional testing could provide a more complete picture. This is especially relevant if your A1C and how you feel day-to-day seem out of step with each other.
Tools that support continuous glucose tracking and pattern awareness β like those available at mdsdiabetes.com β can help you and your care team go beyond a single lab number and understand your full glucose story.
Citation
Mizutani, Uenishi, Onoue (2026). Increased HbA1c relative to actual glycemic control in patients treated with sodium-glucose cotransporter 2 inhibitors. Journal of Diabetes Investigation. PMID: 41235449. DOI: 10.1111/jdi.70191. [Japan] β Nagoya University Graduate School of Medicine, Nagoya, Japan.