Implications and importance of skeletal muscle mass in estimating glomerular filtration rate at dialysis initiation.

There is a trend toward "early" initiation of dialysis for renal replacement therapy. However, several observational studies showed an association of increased mortality at higher estimated glomerular filtration rate (eGFR) at dialysis initiation. This surprising result is due to errors in estimation of glomerular filtration rate (GFR). In malnourished patients with low muscle mass, serum-creatinine-based equations overestimate GFR. In patients with higher muscle mass, these equations underestimate GFR. This spurious association of higher prevalence of malnutrition in patients with higher eGFR compared with those with lower eGFR ultimately leads to the appearance of increased mortality with early initiation of dialysis. Therefore, reliable equations that properly account for creatinine production are warranted to estimate GFR at initiation of dialysis. Until then, in those with extremes of nutrition, mean of measured urea and creatinine clearances might provide more accurate GFR estimation for initiation of dialysis than the currently available equations.