High serum creatinine levels in black patients with chronic kidney disease

A study in the July 2008 issue of the Clinical Journal of the American Nephrological Society (CJASN) reported that, contrary to doctors' belief, this difference may not necessarily reflect age-related differences in muscle mass or body composition.

Led by Dr. Joy Hsu of the University of California, San Francisco School of Medicine, researchers measured the serum creatinine levels of more than 3000 dialysis patients and estimated their body composition. Doctors measure creatinine to estimate a patient's kidney function - high creatinine levels are often a sign of lower kidney function. The creatinine levels of black patients were compared with those of other racial/ethnic groups.

As in previous studies, creatinine levels in black patients were higher than those in non black patients. Dr. Xu explained, "A commonly assumed explanation for this racial difference is that black patients tend to develop end-stage renal disease earlier than whites." "Therefore, black people who undergo dialysis tend to be younger than whites and other ethnic groups, and may therefore have more muscle mass, and creatinine is a natural decomposition product of muscle."

To test this hypothesis, researchers used a technique called bioelectrical impedance analysis to estimate the muscle mass of patients. "We hypothesize that adjusting muscle mass and related factors will eliminate or reduce racial differences in serum creatinine levels," Dr. Xu said

However, even after adjustment, the creatinine level of black patients is still significantly higher than that of black patients. Dr. Xu said, "Compared to non black patients, the higher creatinine levels in black patients cannot be fully explained by differences in age, gender, body size, or muscle mass."

In the United States, the incidence rate of renal diseases in blacks, including end-stage renal disease (ESRD) that requires dialysis or transplantation to replace lost renal function, is much higher than that in whites. The higher serum creatinine level in black patients is another significant difference. "It is not clear how this racial difference in creatinine levels correlates with racial differences in kidney disease," Dr. Xu said.

Dr. Xu added that if muscle mass is not necessarily the answer, more research is needed to find out the real reason why black patients have higher blood creatinine levels than white patients. "Perhaps the answer to this question will help explain why blacks are more vulnerable to progressive chronic kidney disease than whites."

The study, entitled "High serum creatinine levels in black patients with chronic kidney disease: Beyond nutritional status and body composition," will begin on Wednesday, April 16, 2008 Published on the website and will be published in CJASN magazine in July 2008.

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