Renal status among patients using metformin in a primary care setting.

M etformin use has been associated with lactic acidosis, a rare but potentially lethal condition characterized by elevated blood lactate levels ( 5 mmol/l), an increased lactate-to-pyruvate ratio, and an increased anion gap (1). Most cases of metformin-associated lactic acidosis occur in patients with preexisting conditions (e.g., renal insufficiency, hepatic impairment, or heart failure) (2). When used as labeled, metformin may not increase the risk of lactic acidosis beyond what already exists with such conditions (3–5). However, despite evidence suggesting that the risk of lactic acidosis may be reduced if metformin is avoided in patients with renal impairment, and despite the ready availability of serum creatinine tests to assess renal function, inappropriate prescribing of metformin is a concern (2,3,6– 9). The randomized, open-label Glycemic Optimization with Algorithms and Labs At Po1nt of Care (GOAL A1C) study was designed to evaluate the impact of point-of-care versus laboratory testing of glycosylated hemoglobin (A1C) and monitored versus standard titration of insulin glargine on glycemic control in patients with type 2 diabetes inadequately controlled on oral agents. This study also provided an opportunity to assess appropriateness of metformin therapy based on serum creatinine levels at enrollment in a large, predominantly primary care population. This assessment forms the basis of the current report.