title: Checking for completeness of 24-h urine collection using para-amino benzoic acid not necessary in the Observing Protein and Energy Nutrition study.
abstract: OBJECTIVE
  The orally administered para-amino benzoic acid (PABA) is known to have near 100% excretion in urine and is used as a measure of 24-h urine collection completeness (referred to as PABAcheck). The purpose was to examine the effect of including urine collections deemed incomplete based on PABAcheck in a dietary measurement error study.
  
  
  METHODS
  The Observing Protein and Energy Nutrition (OPEN) study was conducted in 1999-2000 and included 484 men and women aged 40-69 years. A food frequency questionnaire and 24-h dietary recalls were evaluated using recovery biomarkers that included urinary nitrogen and potassium from two 24-h urine collections. Statistical modeling determined the measurement error properties of dietary assessment instruments. In the original analyses, PABAcheck was used as a measure of complete urine collection; incomplete collections were either excluded or adjusted to acceptable levels. The OPEN data were reanalyzed including all urine collections and by using criteria based on self-reported missing voids to assess the differences.
  
  
  RESULTS
  Means and coefficients of variation for biomarker-based protein and potassium intakes, and measurement error model-based correlations and attenuation factors were similar regardless of whether PABAcheck or missed voids were considered.
  
  
  CONCLUSIONS
  PABAcheck may not be required in large population-based biomarker studies. However, until there are more analyses evaluating the necessity of a PABAcheck, it is recommended that PABA be given to all participants, but not necessarily analyzed. Then, PABAcheck could be used selectively as a marker of completeness among the collections in which low levels of biomarker are detected or for which noncompliance is suspected.
authors.affiliation: Division of Cancer Control and Population Sciences, US National Cancer Institute, Bethesda, MD 20892-7344, USA. subara@mail.nih.gov
authors.forename: A F
authors.initials: AF
authors.lastname: Subar
authors.forename: D
authors.initials: D
authors.lastname: Midthune
authors.forename: N
authors.initials: N
authors.lastname: Tasevska
authors.forename: V
authors.initials: V
authors.lastname: Kipnis
authors.forename: L S
authors.initials: LS
authors.lastname: Freedman
mesh_terms: D010129:4-Aminobenzoic Acid / Q000652:urine*; D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000652:urine; D004032:Diet; D015930:Diet Records; D004044:Dietary Proteins / Q000008:administration & dosage / Q000652:urine*; D002149:Energy Intake; D005260:Female; D006801:Humans; D008297:Male; D011939:Mental Recall; D008875:Middle Aged; D009584:Nitrogen / Q000008:administration & dosage / Q000652:urine*; D015596:Nutrition Assessment; D009752:Nutritional Status; D017419:Potassium, Dietary / Q000008:administration & dosage / Q000652:urine*; D057566:Self Report; D011795:Surveys and Questionnaires; D059349:Urine Specimen Collection
chemical_list: D015415:Biomarkers; D004044:Dietary Proteins; D017419:Potassium, Dietary; D009584:Nitrogen; D010129:4-Aminobenzoic Acid