Assessment of serum creatinine and kidney function among incident metformin users

Metformin is considered the first-line antihyperglycemic therapy for type 2 diabetes, but should be used with caution in people with renal insufficiency. Our study objective was to describe the proportion of patients who have an assessment of kidney function (serum creatinine [SCr] and estimated glomerular filtration rate [eGFR]) around the time of initiation of metformin in new users.

We used data from the Alberta Kidney Disease Network to identify patients with diabetes (age, ≥66 y) with a new prescription for metformin from November 1, 2002, to March 31, 2008. We assessed whether SCr measurement was completed before and after metformin initiation. The eGFR was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation and categorized into CKD stages. Frequency of metformin use based on SCr measurement and CKD stage was reported using descriptive statistics.

A total of 22 051 subjects were identified as new metformin users. Overall, 25.4% (n=5608) had no measurement of SCr or assessment of eGFR before metformin prescription. In addition, of patients with an eGFR measurement, 38.7% (n=8544) of individuals had an eGFR of less than 60 mL/min/1.73 m(2).

One quarter of patients started on metformin did not have a SCr measurement completed beforehand. Also, metformin was used commonly among patients with diabetes and CKD, potentially putting these individuals at risk for adverse events.