Estimation of glomerular filtration rate in anorectic adolescents

Abstract

Severe malnutrition has been associated with a decrease in fat and lean body mass, as well as in renal function. This study was designed to evaluate the estimation of glomerular filtration rate (GFR, ml/min per 1.73 m²) in malnourished teenagers, by using the formula GFR=kL/P _cr (whereL is body height,P _cr is plasma creatinine concentration and k is a proportionality constant relating muscle mass to body size that has been found to equal 0.7 in adolescent boys and 0.55 in girls). Body composition was estimated using anthropometric measurements and urinary creatinine excretion (U_crV). Malnourished female patients showed depletion of fat and muscle, whereas males had primarily decreased muscle mass. There was a good correlation (r=0.74) between anthropometric [arm muscle volume (AMV)] and chemical U_crV estimates of muscle mass. However, our previously validated estimate of GFR did not give reliable results in this group of malnourished teenagers, probably because their muscle mass was so greatly altered by the severity of malnutrition. Therefore, we used anthropometric measurements and P_cr, to estimate GFR by multiple linear regression. The best prediction was obtained by using AMV/P_cr and the observed/expected (for age, height and sex) weight ratio (WR):

$$\begin{gathered} GFR (ml/min) = 0.06 AMV/P_{{\text{cr}}} + 131{\text{ WR - 79,}} \hfill \\ r = 0.82,n = 13. \hfill \\ \end{gathered} $$

We confirm that malnutrition in adolescents is associated with decreased GFR and conclude that the resulting variability in body composition limits the possibility of estimating GFR from P_cr and height. A somewhat better estimate may be obtained from simple anthropometric measurements and P_cr.