[Concordance of glomerular filtration rate with creatinine clearance in 24-hour urine and Schwartz and Schwartz updated]

Abstract

Background: Reference methods for the quantification of the glomerular filtration rate (GFR) are difficult to use in clinical practice; formulas for evaluating GFR based on serum creatinine (SCr) and/or creatinine clearance are used. The aim of this study was to quantify the correlation and concordance of GFR with creatinine clearance in 24-hour urine (GFR24) and Schwartz and Schwartz updated formulas.

Methods: Cross-sectional study involving healthy pediatric patients and with chronic kidney disease (CKD) from 5 to 16.9 years. Linear correlation between GFR 24 and two formulas was evaluated with the Pearson correlation coefficient (r) and intraclass correlation coefficient (ICC).

Results: We studied 134 patients, of which 59.7% were male. Mean age was 10.8 years. The average GFR24 was 140.34ml/min/1.73m²; 34.3% (n=46) had GFR <90ml/min/1.73m². Moderate linear correlation between GFR24 and Schwartz (r= 0.63) and Schwartz updated (r= 0.65) formulas was observed. There was good concordance between the GFR24 and Schwartz (ICC= 0.77) and updated Schwartz (ICC= 0.77) formulas. Schwartz classical formula in patients with GFR24 ≥ 90ml/min/1.73m² estimated higher values, while Schwartz updated underestimated values.

Conclusions: There is moderate correlation and good concordance between the GFR24 and Schwartz and Schwartz updated formulas. The concordance was better in patients with obesity and lower in women, patients with hyperfiltration and normal weight.

Keywords: Enfermedades del riñón; Glomerular filtration rate; Insuficiencia renal; Kidney diseases; Renal insufficiency; Tasa de filtración glomerular.