Within-person variability in urinary phthalate metabolite concentrations: measurements from specimens after long-term frozen storage.

Author(s): Baird DD, Saldana TM, Nepomnaschy PA, Hoppin JA, Longnecker MP, Weinberg CR, Wilcox AJ

Publication: J Expo Sci Environ Epidemiol, 2010, Vol. 20, Page 169-75

PubMed ID: 19277068 PubMed Review Paper? No

Purpose of Paper

Conclusion of Paper

Studies

1. Study Purpose

   The purpose of this study was to determine the effects of long-term frozen storage (22-24 y), daily variability, and stage in menstrual cycle on phthalate metabolite concentrations in urine specimens from women. First morning urine specimens underwent at least 2 freeze-thaw cycles prior to the present study. The specimens subjected to long-term frozen storage did not undergo similar analysis prior to long-term storage, but the authors compared their results to another study which measured phthalate metabolites in more recently collected specimens.

   Summary of Findings:

   Concentrations of all three DEHP metabolites (mono-(2-ethylhexyl) phthalate (MEHP); mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP); and mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP)) within each specimen were highly correlated after 22-24 y of frozen storage, suggesting long-term stability. For all metabolites examined except MEP, average levels were higher in this study (specimens collected in 1983-1985) than reported for NHANES urine specimens collected in 1999-2000 or in 2001-2002 which were analyzed after a much shorter (unspecified) storage period, again suggesting long-term stability. For all metabolites except MEP, concentrations were more closely correlated in specimens collected 4 weeks apart and likely during the same menstrual cycle phase than those collected 2 weeks apart, but metabolites were not specifically associated with menstrual cycle phase. Intraclass correlation coefficients for the 7 metabolites, based on 3 samples taken during a 4 week period, ranged from 0.21-0.53, showing low to moderate reproducibility over a 4 week interval. The three DEHP metabolites, MEHP, MEHHP, and MEOHP, showed significantly higher levels in specimens collected in 1984 than specimens collected in 1983 or 1985. The other four metabolites measured (mono-methyl phthalate (MMP); MEP; mono-n-butyl phthalate and mono-isobutyl phthalate (MnBP); and mono-benzyl phthalate (MBzP)) were not significantly different between collection years.

   Biospecimens

   • Bodily Fluid - Urine

   Preservative Types

   • Frozen

   Diagnoses:

   • Normal

   Platform:

   Analyte	Technology Platform
   Small molecule	LC-MS or LC-MS/MS

   Pre-analytical Factors:

   Classification	Pre-analytical Factor	Value(s)
   Biospecimen Acquisition	Time of biospecimen collection	During luteal phase of menstrual cycle During follicular phase of menstrual cycle
   Storage	Storage duration	22 y (from 1985) 23 y (from 1984) 24 y (from 1983)

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