title: Para-aminobenzoic acid (PABA) used as a marker for completeness of 24 hour urine: effects of age and dosage scheduling.
abstract: OBJECTIVE
  To examine the age dependency of the urinary para-aminobenzoic acid (PABA) excretion, and if a delayed PABA excretion can be overcome by advancing intake schedule; and to examine the recovery of PABA in fractionated urinary samples collected during 24 h after single and repeated doses of PABA.
  
  
  METHODS
  Cross-over study with subjects randomized to start with recommended schedule of PABA administration (80 mg at 08:00, 12:00 and 18:00; PABA18) and then an advanced schedule (80 mg at 08:00, 12:00 and 15:00; PABA15) or vice versa. One subgroup of eight subjects collected individual urine specimens for 24 h after a morning dose of 80 mg of PABA, and another subgroup of 10 subjects collected individual urine specimens for 24 h after ingestion of 80 mg of PABA three times at mealtimes.
  
  
  METHODS
  Employees and relatives from the Danish Food Administration.
  
  
  METHODS
  Ninety-nine healthy volunteers (61 females and 38 males) aged 30-91 y.
  
  
  RESULTS
  Linear regressions for PABA15 and PABA18 demonstrate significantly less recovery with age (PABA15: r(2)=0.1784, P=0.0002; PABA18: r(2)=0.1273, P=0.0019). Linear regression of DeltaPABA (PABA15-PABA18) with age showed the best fit line to be horizontal (slope -0.0066, P=0.89; 95% CI -0.1046, 0.0915) and with a Y-intercept not significantly different from 0 (1.575; 95% CI -4.176, 7.326). In this population the lower limit for complete 24 h urine collection was 79.2%. After a single dosage of 80 mg PABA 70-85% was recovered after 8 h. Within 16 h after ingestion of 240 mg PABA at recommended hours the lowest acceptable recovery (78.1%) was reached.
  
  
  CONCLUSIONS
  There is a gradual decline of PABA recovery with age that cannot be overcome by advancing the dosage schedule. Because of a lower delimiting PABA recovery for the elderly, some 24 h collections in this age group will be rejected unjustly (false-negatives). Also, with the currently recommended dosage schedule (PABA taken with the main meals) the risk of false-positive 24 h urine collections prevails. With refinement of the PABA test procedure, ie employing a specific analytical method and age-dependent cut-off values, the test may achieve a higher specificity and sensitivity.
authors.affiliation: Danish Veterinary and Food Administration, Institute of Food Research and Nutrition, Søborg, Denmark.
authors.forename: J
authors.initials: J
authors.lastname: Jakobsen
authors.forename: A N
authors.initials: AN
authors.lastname: Pedersen
authors.forename: L
authors.initials: L
authors.lastname: Ovesen
mesh_terms: D010129:4-Aminobenzoic Acid / Q000008:administration & dosage / Q000652:urine*; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology / Q000652:urine*; D015415:Biomarkers / Q000652:urine; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D018592:Cross-Over Studies; D004334:Drug Administration Schedule; D005188:False Negative Reactions; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D015415:Biomarkers; D010129:4-Aminobenzoic Acid