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. ¹²⁵Iodine-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 m², C(SCH) overestimated GFR by only 0.1% ± 3%, but when C(IO) was ≤ 15 ml/min per 1.73 m², C(SCH) overestimated GFR by 164% ± 42%. When renal function is normal or mildly reduced (GFR > 50 ml/min per 1.73 m²), 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 ≤ 50 ml/min per 1.73 m²). We conclude that C(SCH) is valid in predicting GFR only in children with normal renal function and mild insufficiency.