title: A prospective study of protein excretion using short-interval timed urine collections in patients with lupus nephritis.
abstract: The 24-h urine protein-to-creatinine ratio is the gold standard in evaluating proteinuria in lupus nephritis; however, the urine collection is inconvenient to the patient. Random spot urine protein-to-creatinine ratios, although convenient, have poor agreement with the 24-h ratios in these patients. Here, we sought to define a timed collection interval providing accurate and precise data and patient convenience. Urine from 41 patients, in 2 medical centers, with biopsy-proven lupus nephritis was collected at 6-h intervals for 24 h. The protein-to-creatinine ratio of each short collection was then compared with that of a 24-h collection made by combining the 6-h samples. A first morning void and spot urine samples were collected before and after the 24-h collection, respectively. There was significant diurnal variation with peak proteinuria at 6-12 h and nadir at 18-24 h. Each 6-h collection showed excellent correlation and concordance with the 24-h protein-to-creatinine ratio, but the 12-24-h interval had the best agreement. In contrast to the random spot urines, the first morning void also had excellent correlation and concordance, but underestimated the 24-h protein-to-creatinine ratio. Our study shows that a 12-h overnight urine collection is the best surrogate, with excellent agreement with the 24-h protein-to-creatinine ratio, and it is convenient for patients. There was little variability between centers, an important feature for clinical trials.
authors.affiliation: Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA. dfine1@jhmi.edu
authors.forename: Derek M
authors.initials: DM
authors.lastname: Fine
authors.forename: Martina
authors.initials: M
authors.lastname: Ziegenbein
authors.forename: Michelle
authors.initials: M
authors.lastname: Petri
authors.forename: Ernest C
authors.initials: EC
authors.lastname: Han
authors.forename: Alison M
authors.initials: AM
authors.lastname: McKinley
authors.forename: Jerry W
authors.initials: JW
authors.lastname: Chellini
authors.forename: Haikady N
authors.initials: HN
authors.lastname: Nagaraja
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Carson
authors.forename: Brad H
authors.initials: BH
authors.lastname: Rovin
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D003404:Creatinine / Q000652:urine; D005260:Female; D006801:Humans; D008181:Lupus Nephritis / Q000652:urine*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011507:Proteinuria / Q000175:diagnosis* / Q000652:urine*; D015203:Reproducibility of Results; D013997:Time Factors; D055815:Young Adult
chemical_list: D003404:Creatinine