Urinary 4-pyridoxic acid excretion in 24-hour versus random urine samples as a measurement of vitamin B6 status in humans

Am J Clin Nutr. 1984 Mar;39(3):466-70. doi: 10.1093/ajcn/39.3.466.


Urinary excretion of 4-pyridoxic acid (4PA) in 19 men (n = 5) and women (n = 14) was measured to evaluate the validity of determining the 4PA/creatinine ratio in random urine samples as an alternative to total 24-h 4PA excretion in assessing vitamin B6 nutritional status. The relationships among dietary vitamin B6 intake, 4PA excretion, plasma pyridoxal 5'-phosphate levels, and erythrocyte aspartate aminotransferase activity and in vitro stimulation by added plasma pyridoxal 5'-phosphate were examined. The subjects consumed all meals for 3 days in a metabolic unit, and protein intake was kept constant. Plasma pyridoxal 5'-phosphate concentration was positively correlated with vitamin B6 intake of the previous day (r = 0.61, p less than 0.01). There was a positive correlation (r = 0.59, p less than 0.01) between total 4PA and 4PA/creatinine in the 24-h urine samples. No difference (p greater than 0.05) in 4PA/creatinine between the 24-h samples and either morning or afternoon random samples taken the next day was found. These findings support the use of the 4PA/creatinine ratio in random urine samples as an alternative to 24-h urinary 4PA excretion.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Aspartate Aminotransferases / blood
  • Creatinine / urine
  • Erythrocytes / enzymology
  • Female
  • Humans
  • Isonicotinic Acids / urine*
  • Male
  • Pyridoxal Phosphate / blood
  • Pyridoxic Acid / urine*
  • Pyridoxine / administration & dosage*
  • Specimen Handling
  • Time Factors
  • Vitamin B 6 Deficiency / diagnosis*
  • Vitamin B 6 Deficiency / urine


  • Isonicotinic Acids
  • Pyridoxic Acid
  • Pyridoxal Phosphate
  • Creatinine
  • Aspartate Aminotransferases
  • Pyridoxine