Urine collection for protein excretion

Abstract

To the Editor: The major outcome variable in the study by Ellis et al1.Ellis D Vats A Moritz M.L Reitz S Grosso M.J Janosky J.E Long-term antiproteinuric and renoprotective efficacy and safety of losartan in children with proteinuria.J Pediatr. 2003; 143: 89-97Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar is the 24-hour urine collection for protein excretion. The authors stated, “Validation of urine collections was ascertained from creatinine excretion per kilogram body weight for sex, age and body habitus.” They reference an article by Barnett et al2.Barratt T.M McLaine P.N Soothill J.F Albumin excretion as a measure of glomerular dysfunction in children.Arch Dis Child. 1970; 45: 496-501Crossref PubMed Scopus (51) Google Scholar in which 8 children had 24-hour urine collections. Age, sex, and creatinine excretion rates were not reported. Possibly Ellis et al wanted to refer to the work of Ghazali and Barratt,3.Ghazali S Barratt T.M Urinary excretion of calcium and magnesium in children.Arch Dis Child. 1974; 49: 97-101Crossref PubMed Scopus (214) Google Scholar in which 24-hour urine collections were obtained from “54 apparently healthy children 1–15 years.” No sexes were given. The following equation was presented: Alternatively, Ellis et al may have used the equation Barratt and Counahan reported in a letter to the editor4.Barratt T.M Counahan R Correlates of creatinine excretion.N Engl J Med. 1977; 296: 176PubMed Google Scholar that stated, “We reported that in healthy children three to 15 years of age, creatinine excretion (mg/kg body weight/day) was 15 + 0.5 × age (years) 3 (S.D.).” Twelve percent of urine collections in the paper by Ellis et al were considered “inadequate”.1.Ellis D Vats A Moritz M.L Reitz S Grosso M.J Janosky J.E Long-term antiproteinuric and renoprotective efficacy and safety of losartan in children with proteinuria.J Pediatr. 2003; 143: 89-97Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar These collections were apparently detected using an equation. Protein excretion was “corrected” by multiplying the Pr/Cr ratio by the creatinine excretion rate from the same unidentified equation. Not knowing how they evaluated and “corrected” the 24-hour urine volumes is a serious defect in this report. There are a number of publications with equations for creatinine excretion rates related to age and sex.5.Graystone J.E Creatinine excretion during growth.in: Cheek D.B Human growth. Lea & Febiger, Philadelphia (PA)1968: 182-197Google Scholar, 6.Schwartz G.J Gauthier B A simple estimate of glomerular filtration rate in adolescent boys.J Pediatr. 1985; 106: 522-526Abstract Full Text PDF PubMed Scopus (341) Google Scholar, 7.Schwartz G.J Does kL/PCr estimate GFR, or does GFR determine k?.Pediatr Nephrol. 1992; 6: 512-515Crossref PubMed Scopus (41) Google Scholar, 8.Hellerstein S Simon S.D Berenbom M Erwin P Nickell E Creatinine excretion rates for renal clearance studies.Pediatr Nephrol. 2001; 16: 637-643Crossref PubMed Scopus (17) Google Scholar ReplyThe Journal of PediatricsVol. 144Issue 6Preview Full-Text PDF