Background: It has been suggested that serum cystatin C (cyst-C)
concentration provides a better indication of changes in glomerular filtration rate
(GFR) than does serum creatinine concentration.
Methods: Because of conflicting results as to the usefulness of cyst-C,
we compared the GFRs calculated from serum cyst-C, inulin clearance and endogenous
creatinine clearance in children. GFRs calculated from cystatin concentration, inulin
clearance following a single injection and endogenous creatinine clearance using
Jaffé and enzymic methods were compared in 66 children (1·3-21·9 years) with a
variety of renal disorders. Receiver operating curve analysis was used to determine
the cut-off value that would give the best discrimination between normal and
decreased GFR.
Results: The serum cyst-C concentration ranged from 0·66 to 7·61 mg/L
(median 1·94). Serum creatinine Jaffé concentration (creat-J) ranged from 38 to 871
µmol/L (median 105) and creatinine enzymatic concentration
(creat-E) ranged from 28 to 862 µmol/L (median 126). The linear
correlation coefficient (R) of 1/cyst-C versus GFR
(R = 0·937) did not differ from either that of 1/creat-J versus
GFR (R = 0·918) or that of 1/creat-E versus GFR (R
= 0·901). These coefficients had overlapping confidence intervals. The areas under
the curve for cyst-C, creat-J and creat-E were 0·967, 0·977 and 0·924, respectively,
and were not significantly different from each other. For cyst-C, the optimal cut-off
was 1·1 mg/L.
Conclusions: Serum cyst-C is equivalent to creat-J and creat-E as a
marker for estimating the GFR in the paediatric population studied.
