Serum Creatinine, Height, and Weight Do Not Predict Glomerular Filtration Rate in Children with IDDM

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Abstract
OBJECTIVE: To assess the validity of two equations: K × height/serum creatinine (KL/Cr; K = 0.55 for females 1–18 yr of age and 0.7 for males 12–18 yr of age) and (140 – age) × weight/72 × creatinine (×0.85 for women; Cockroft-Gault) in estimating glomerular filtration rate in children and adolescents with IDDM. RESEARCH DESIGN AND METHODS: From the records of the Children's Hospital Diabetes Clinic, we selected 70 patients with GFR determined by 99mTc-labeled DTPA plasma clearance, stable renal function, and simultaneous measurements of height, weight, blood pressure, HbA1c, and plasma creatinine. We compared DTPA-GFR with estimated GFR from KL/Cr and Cockroft-Gault equations for three groups: all patients, patients with DTPA-GFR ≤ 140 ml·min−1 · 1.73 m−2, and patients with DTPA-GFR > 140 ml·min−1 · 1.73 m−2. RESULTS: For all patients, mean values for DTPA-GFR = 147 (95% confidence interval, 139–155), for KL/Cr = 118 (110–125), and for Cockroft-Gault = 84 ml–·min−1 · 1.73 m−2 (78–90). For patients with DTPA-GFR ≤ 140, DTPA-GFR = 123 (117–128), KL/Cr = 110 (100–119), and Cockroft-Gault = 92 (82–102). For patients with DTPA-GFR > 140, DTPA-GFR = 167 (158–177), KL/Cr = 125 (114–136), and Cockroft-Gault = 77 (71–84). Linear regression analysis showed significant (P < 0.05) relationships for KL/Cr only in patients with DTPA-GFR ≤ 140 (r = 0.29), for Cockroft-Gault in all patients (r = −0.46), and for patients with DTPA-GFR ≤ 140 (r = −0.31). Determination of a revised K for use in KL/Cr from individual calculations of K (DTPA-GFR × Cr/L) yielded an average value of 0.70 (SD = 0.11). With the use of K = 0.7, the mean KL/Cr value for patients with DTPA-GFR ≤ 140 ml·min−1 · 1.73 m−2 was 125 ± 27 (95% confidence interval, 115–135), compared with a DTPA-GFR value of 123 ± 14 (95% confidence interval, 117–128). CONCLUSIONS: KL/Cr and Cockroft-Gault do not accurately estimate DTPA plasma clearance. We recommend the use of K equal to 0.70 when estimating GFR in children and adolescents with IDDM and DTPA-GFR ≤ 140 using KL/Cr and do not recommend the use of the KL/Cr (for patients with DTPA-GFR > 140) or the Cockroft-Gault equation in this population.

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