Para-aminobenzoic acid used as a marker for completeness of 24 hour urine: assessment of control limits for a specific HPLC method.
OBJECTIVE
The study comprised three protocols. Protocol 1 compared a HPLC method with the commonly employed colorimetric diazocoupling method. Protocol 2 examined, if the last dosage of p-aminobenzoic acid (PABA) could be advanced in the old to allow for a delayed age-dependent urinary excretion of PABA. Protocol 3 established limits for recovery of PABA in 24 h urine applying the HPLC method.


METHODS
A total of 151 healthy volunteers participated in the study of which 140 were accepted. In protocol 1: 37 subjects aged 20-78 y were included. All subjects took PABA as recommended (80 mg orally at 08.00, 12.00 and 18.00 h). Protocol 2: compared urinary PABA excretion in two groups of 80 y old subjects who had their last PABA dosage administered at 15.00 h (n = 16) and at 18.00 h (n = 31), respectively. Protocol 3: comprised 56 subjects aged 20-80 y. In the younger age group (20-59 y; n = 34) PABA was taken as recommended, whereas in the older age group (60-80 y; n = 22) the last PABA dosage was advanced three hours.


RESULTS
Protocol 1: HPLC gave significantly lower PABA recovery results compared to colorimetry, the difference between methods being 23.9 +/- 8.5 mg/24 h (P < 0.001). Protocol 2: higher PABA recoveries were demonstrated with the advanced dosage schedule compared to the recommended schedule (208 +/- 14 mg/24 h vs 181 +/- 22 mg/24 h; P < 0.001). Protocol 3: PABA recovery with HPLC was 211 +/- 12 mg/24 h, and the lower limit comprising 95% of subjects was 187 mg/24 h. Similar PABA recoveries were demonstrated in the younger subjects and the older subjects (211 +/- 11 mg/24 h vs 211 +/- 13 mg/24 h; NS).


CONCLUSIONS
An advanced dosage schedule for PABA in the aged is recommended. Because of lower recoveries with HPLC, the low limit for recovered PABA in a complete 24 h urine differs from the limit based on colorimetry. This study found a limit of 187 mg/24 h corresponding to the lower 95% confidence limit for a single subject.
Institute of Food Chemistry and Nutrition, National Food Agency, Copenhagen, Denmark.
J
J
Jakobsen
L
L
Ovesen
S
S
Fagt
A N
AN
Pedersen
D010129:4-Aminobenzoic Acid / Q000008:administration & dosage / Q000652:urine; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology* / Q000652:urine; D015415:Biomarkers / Q000652:urine; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003124:Colorimetry / Q000379:methods; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D013997:Time Factors
D015415:Biomarkers; D010129:4-Aminobenzoic Acid