title: Circadian rhythm of proteinuria: consequences of the use of urinary protein:creatinine ratios.
abstract: Proteinuria in patients with glomerular disease has a circadian rhythm, but for creatinine such a rhythm is either absent or of low amplitude. We found in 18 of 23 admitted patients (group I) and in seven outpatients (group II) a marked circadian rhythm of the protein: creatinine ratio. Estimates of 24-h proteinuria were obtained by multiplying the protein:creatinine ratio of 3-h urine samples with 24-h creatinine excretion, calculated from age, sex and bodyweight. Estimated proteinuria could be as low as 19% or as high as 349% of actually measured 24-h proteinuria; the mean SD was 23%. The best estimate was obtained with the 06.00-09.00 hours urine samples. The estimates correlated better with actually measured 24-h proteinuria than the protein: creatinine ratio per se correlated with the 24-h proteinuria. Day-to-day variation of proteinuria estimates from samples taken at the same time of the day was of similar magnitude as day-to-day variation of actual 24-h proteinuria. We conclude that the usefulness of the protein: creatinine ratio of a random urine sample for estimation of proteinuria is limited, because of the circadian rhythm of proteinuria. However, samples collected at a fixed time of the day are an acceptable alternative for 24-h urine collections in the clinical follow-up of individual patients.
authors.affiliation: Department of Nephrology, Academic Medical Centre, Amsterdam, The Netherlands.
authors.forename: M G
authors.initials: MG
authors.lastname: Koopman
authors.forename: R T
authors.initials: RT
authors.lastname: Krediet
authors.forename: G C
authors.initials: GC
authors.lastname: Koomen
authors.forename: J
authors.initials: J
authors.lastname: Strackee
authors.forename: L
authors.initials: L
authors.lastname: Arisz
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002940:Circadian Rhythm; D003404:Creatinine / Q000652:urine*; D005260:Female; D005921:Glomerulonephritis / Q000652:urine; D006801:Humans; D008297:Male; D008875:Middle Aged; D011507:Proteinuria / Q000652:urine*
chemical_list: D003404:Creatinine