A recent study in Diabetes Care concluded that more patients would be eligible for metformin use if estimated glomerular filtration rate (eGFR) were used to define kidney disease rather than serum creatinine (sCr). Researchers used data from the 1999 to 2010 National Health and Nutrition Examination Survey (NHANES) to analyze 3,902 adult participants with diabetes (defined by self-report or an HbA1c ≥6.5%).

Across all 12 years, 66.4% of adults with diabetes were treated with a diabetes medication, and this percentage increased over time, from 61.3% in 1999 to 2000 to 69.7% in 2009 to 2010. Metformin use among those with diabetes increased from 26.1% to 44.5%.

8.8% were ineligible for metformin because of the FDA's contraindication among individuals with sCr ≥1.4 mg/dL for women and ≥1.5 mg/dL for men. Researchers also looked at the patients using (eGFR) categories: likely safe to take metformin, ≥45 mL/min/1.73 m2; contraindicated, <30 mL/min/1.73 m2; and indeterminate, 30 to 44 mL/min/1.73 m2.

Among individuals ineligible for metformin using conventional sCr thresholds, 14.6% had an eGFR ≥45 mL/min/1.73 m2 and 50% had an eGFR between 30 and 44 mL/min/1.73 m2. Only 35.7% of study participants would be ineligible for metformin based on an eGFR <30 mL/min/1.73 m2.

Evidence has shown eGFR to be a more accurate estimate of kidney function than sCr, the authors noted. Limitations of the study was that they could not determine the reasoning behind low levels of metformin use, which could include non-renal clinical conditions that contraindicate the use of metformin, such as liver disease.

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