Limitations to body length/serum creatinine ratio as an estimate of glomerular filtration in children

The ability of the Schwartz formula (C-SCH) to estimate glomerular filtration rate (GFR) accurately was investigated in children with renal disease. (125)Iodine-iothalamate clearance (C-IO) was used as the reference standard for measuring GFR. Data from 176 C-IO studies performed on 133 children (aged between 1 and 18 years) were compared with the simultaneous estimation of GFR by C-SCH. The overestimation of GFR by C-SCH was inversely proportional to the level of renal function. When C-IO was >90 ml/min per 1.73 m(2), C-SCH overestimated GFR by only 0.1%+/-3%, but when C-IO was less than or equal to 15 ml/min per 1.73 m(2), C-SCH overestimated GFR by 164%+/-42%. When renal function is normal or mildly reduced (GFR >50 ml/min per 1.73 m(2)), C-SCH overestimated C-IO by only 10.3+/-3.0%, compared with 90.3+/-14.5% when renal function was moderately to severely curtailed (GFR less than or equal to 50 ml/min per 1.73 m(2)). We conclude that C-SCH is valid in predicting GFR only in children with normal renal function and mild insufficiency.