Editing Niacin (section)

===Measuring vitamin status===
Plasma concentrations of niacin and niacin metabolites are not useful markers of niacin status.<ref name="DRItext"/> Urinary excretion of the methylated metabolite N1-methyl-nicotinamide is considered reliable and sensitive. The measurement requires a 24-hour urine collection. For adults, a value of less than 5.8 μmol/day represent deficient niacin status and 5.8 to 17.5 μmol/day represents low.<ref name="DRItext"/> According to the World Health Organization, an alternative mean of expressing urinary N1-methyl-nicotinamide is as mg/g creatinine in a 24-hour urine collection, with deficient defined as <0.5, low 0.5-1.59, acceptable 1.6-4.29, and high >4.3<ref name="Pellagra And Its Prevention" /> Niacin deficiency occurs before the signs and symptoms of pellagra appear.<ref name="DRItext"/> Erythrocyte [[nicotinamide adenine dinucleotide]] (NAD) concentrations potentially provide another sensitive indicator of niacin depletion, although definitions of deficient, low and adequate have not been established. Lastly, plasma [[tryptophan]] decreases on a low niacin diet because tryptophan converts to niacin. However, low tryptophan could also be caused by a diet low in this essential [[amino acid]], so it is not specific to confirming vitamin status.<ref name="DRItext"/>