Diagnostic sensitivity of serum cystatin for impaired glomerular filtration rate

Recently, the reciprocal of cystatin C (Cys-C), a non-glycosylated 13-kilod alton protein that is produced by all investigated nucleated cells, was fou nd to correlate closely with glomerular filtration rate (GFR). In order to determine the diagnostic validity in children for the detection of impaired GFR, venous blood samples from 381 children (aged 1.7-18 years) with vario us renal pathology referred for Cr-51-EDTA clearance investigations were ob tained for measurement of Cys-C as well as beta(2)-microglobulin (beta(2)-M G) and serum creatinine. Two hundred and sixteen children with clearance va lues >90 ml/min per 1.73 m(2) constituted a control group, with a normal GF R. In the control group, Cys-C values were normally distributed with a mean of 0.94+/-0.27 mg/l and an upper reference limit (97.5th percentile) of 1. 47 mg/l. In all children, there was a positive correlation between 51Cr-EDT A clearance and the reciprocal of Cys;C (r = 0.64, P < 0.0001), beta(2)-MG (r = 0.59, P < 0.0001), creatinine (r = 0.55, P < 0.0001), and the height/c reatinine ratio (r = 0.73, P < 0.0001). Receiver-operating characteristics analysis showed that there were no significant differences between these th ree parameters for discriminating between patients with normal and reduced C;FR, although there was a tendency towards the best diagnostic sensitivity of the GFR estimate according to the Schwartz formula. We conclude that fo r the detection of mildly impaired GFR, a full clearance study cannot be re placed by measurement of serum Cys-C or beta(2)-MG concentrations.