Relationship between hematocrit and renal function in men and women

Abstract

Background Anemia is a known complication of renal insufficiency, but the relationship between level of renal function and magnitude of reduction in hematocrit is not well defined. Men have higher hematocrit and absolute glomerular filtration rate (GFR) than women; however, it is unknown whether the level of clearance associated with decreased hematocrit is the same in men and women. Methods. We conducted a cross-sectional study of 12,055 adult ambulatory patients. General linear models were used to analyze the relationship between hematocrit and Cockcroft-Gault equation estimated creatinine clearance (Ccr; mL/min) and Modification of Diet in Renal Disease (MDRD) formula estimated the GFR indexed to body surface area (mL/min/1.73 m2). Results. The hematocrit decreased progressively below estimated Ccr 60 mL/min in men and 40 mL/min in women. Compared with subjects with Ccr >80 mL/min, men with Ccr 60 to 50 mL/min, 50 to 40 mL/min, 40 to 30 mL/min, 30 to 20 mL/min, and ≤20 mL/min had mean hematocrits that were lower by 1.0, 2.4, 3.7, 3.5, and 10.0%, respectively; the corresponding reductions in women with Ccr 40 to 30 mL/min, 30 to 20 mL/min, and ≤20 mL/min were 1.7, 2.9, and 6.3% (all P < 0.05). This between-sex difference diminished when renal function measurement was indexed to body size. Compared with subjects with GFR >80 mL/min/1.73 m2, men with GFR 50 to 40 mL/min/min/1.73 m2, 40 to 30 mL/min/1.73 m2, 30 to 20 m L/min/1.73 m2 and ≤20 mL/min/1.73 m2 were 0.6, 1.6, 3.8, and 5.3% (all P <0.05). Conclusions. A decrease in hematocrit is apparent even among patients with mild to moderate renal insufficiency. At any given level of renal function below estimated Ccr 60 mL/min, men have a larger decrease in hematocrit than women.