Association of kidney function with anemia: the Third National Health and Nutrition Examination Survey (1988-1994).

BACKGROUND: Kidney failure is known to cause anemia, which is associated with a higher risk of cardiac failure and mortality. The impact of milder decreases in kidney function on hemoglobin levels and anemia in the US population, however, is unknown.
METHODS: We analyzed a population-based sample of 15419 participants 20 years and older in the Third National Health and Nutrition Examination Survey, conducted from 1988 to 1994.
RESULTS: Lower kidney function was associated with a lower hemoglobin level and a higher prevalence and severity of anemia below, but not above, an estimated glomerular filtration rate (GFR) of 60 mL/min per 1.73 m(2). Adjusted to the age of 60 years, the predicted median hemoglobin level among men (women) decreased from 14.9 (13.5) g/dL at an estimated GFR of 60 mL/min per 1.73 m(2) to 13.8 (12.2) g/dL at an estimated GFR of 30 mL/min per 1.73 m(2) and to 12.0 (10.3) g/dL at an estimated GFR of 15 mL/min per 1.73 m(2). The prevalence of anemia (hemoglobin level <12 g/dL in men and <11 g/dL in women) increased from 1% (95% confidence interval, 0.7%-2%) at an estimated GFR of 60 mL/min per 1.73 m(2) to 9% (95% confidence interval, 4%-19%) at an estimated GFR of 30 mL/min per 1.73 m(2) and to 33% (95% confidence interval, 11%-67%) at an estimated GFR of 15 mL/min per 1.73 m(2) among men and to 67% (95% confidence interval, 30%-90%) at an estimated GFR of 15 mL/min per 1.73 m(2) among women. An estimated GFR of 15 to 60 mL/min per 1.73 m(2) was present in 4% of the entire population and in 17% of the individuals with anemia.
CONCLUSION: Below an estimated GFR of 60 mL/min per 1.73 m(2), lower kidney function is strongly associated with a higher prevalence of anemia among the US adult population.