title: Temporal variability in urinary phthalate metabolite excretion based on spot, morning, and 24-h urine samples: considerations for epidemiological studies.
abstract: Urinary phthalate excretion is used as marker of phthalate exposure in epidemiological studies. Here we examine the reliability of urinary phthalate levels in exposure classification by comparing the inter- and intrasubject variation of urinary phthalate metabolite levels. Thirty-three young healthy men each collected two spot, three first-morning, and three 24-h urine samples during a 3-month period. Samples were analyzed for the content of 12 urinary metabolites of 7 different phthalates. Variability was assessed as intraclass correlation coefficients (ICC). For the metabolites of diethyl-, dibutyl-, and butylbenzyl-phthalates moderate ICCs were observed in all three sample types, albeit highest in 24-h urine (0.51-0.59). For the metabolites of di(2-ethylhexyl) phthalate and di-iso-nonyl phthlates lower ICCs (0.06-0.29) were found. These low ICCs indicate a high risk of misclassification of exposures for these two phthalates in population studies and hence an attenuation of the power to detect possible exposure-outcome associations. The only slightly higher ICCs for 24-h pools compared to first-morning and spot urine samples does not seem to justify the extra effort needed to collect 24-h pools.
authors.affiliation: Department of Growth and Reproduction, Rigshospitalet, Copenhagen University Hospital, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Hanne
authors.initials: H
authors.lastname: Frederiksen
authors.forename: Selma K
authors.initials: SK
authors.lastname: Kranich
authors.forename: Niels
authors.initials: N
authors.lastname: Jørgensen
authors.forename: Olivier
authors.initials: O
authors.lastname: Taboureau
authors.forename: Jørgen H
authors.initials: JH
authors.lastname: Petersen
authors.forename: Anna-Maria
authors.initials: AM
authors.lastname: Andersson
mesh_terms: D000293:Adolescent; D004781:Environmental Exposure / Q000032:analysis*; D004785:Environmental Pollutants / Q000378:metabolism / Q000652:urine*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D010795:Phthalic Acids / Q000378:metabolism / Q000652:urine*; D055815:Young Adult
chemical_list: D004785:Environmental Pollutants; D010795:Phthalic Acids; C032279:phthalic acid