Delanaye P et al. (2008) Cystatin C or creatinine for detection of stage 3 chronic kidney disease in anorexia nervosa. Nephron Clin Pract 110: c158–c163

Renal disease occurs in over 70% of patients with anorexia nervosa. Detection of chronic kidney disease (CKD) in this group is, however, difficult as serum creatinine measurements are affected by the reduced muscle mass. Delanaye et al. investigated the value of cystatin C as an alternative marker of renal failure in patients with anorexia nervosa.

The researchers recruited 27 patients with anorexia nervosa (mean age 30 ± 13 years, 25 women) who had a BMI <18 kg/m2 (mean 15 ± 2 kg/m2). Glomerular filtration rate (GFR) was measured in all patients using 51Cr–ethylenediaminetetraacetate clearance (mean 68 ± 23 ml/min); 9 were classified as having stage 3 CKD (GFR <60 ml/min/1.73 m2) and 16 were diagnosed with stage 2 CKD (GFR 60–90 ml/min/1.73 m2). Serum creatinine concentration was not notably correlated with GFR; however, the reciprocal of the plasma cystatin C level showed a strong correlation with GFR (coefficient of correlation r = 0.62; P <0.001). Detection of decreased kidney function (defined as GFR <60 ml/min/1.73 m2) was achieved with greater sensitivity and specificity by use of plasma cystatin C measurements (67% and 100%, respectively, at the optimal cut-off point) than by serum creatinine level (56% and 78%, respectively, at the optimal cut-off point).

Plasma cystatin C concentrations are not influenced by muscle mass, which explains why cystatin C seems to be a better marker of renal function than is serum creatinine in patients with anorexia nervosa. The authors recommend confirmation of these results in a larger study population.