The epidemiology of hemoglobin levels in patients with type 2 diabetes.

Background: Anemia is a common finding in patients with diabetes, for whom it constitutes an additional burden. The aim of this study is to clarify the natural history of anemia in patients with type 2 diabetes and describe factors that predict a decrease in hemoglobin (Hb) levels.

Methods: A 5-year prospective cohort study was designed as a follow-up of 503 individuals with type 2 diabetes in a single diabetes clinic. In addition to standard management, a full blood count was obtained at each routine visit. No intervention was undertaken to modify Hb levels.

Results: At baseline, 12% of patients had anemia, and an additional 13% developed anemia during follow-up. Overall Hb levels decreased by -0.07 +/- 0.01 g/dL/y, suggesting that anemia is the end point of a process that begins more than 10 years previously with the initiation of vascular damage. The greatest decreases in Hb levels were seen in patients with macroalbuminuria, renal impairment, or established macrovascular disease at baseline (all P < 0.01). In patients with microvascular disease, decreasing Hb levels tracked with decreasing glomerular filtration rates (GFRs). Patients with an estimated GFR greater than 90 mL/min/1.73 m2 (>1.5 mL/s) or normoalbuminuria had stable Hb levels during the 5-year follow-up. In patients with anemia in our cohort who were managed conservatively, Hb levels decreased by 0.09 +/- 0.03 g/dL/y. This decrease was associated with HbA1c levels, but not renal function.

Conclusion: This study defines the natural history of Hb levels in patients with type 2 diabetes. Early identification of anemia may be achieved by means of annual or biannual screening in high-risk groups with nephropathy, advanced age, or macrovascular disease. These data are important for developing a rational response to the prevention and management of anemia.