Assessment of the level of nutrition. A method for the estimation of nicotinic acid in urine

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Abstract
The urine is heated with NaOH, to convert any amide into the acid, and neutralized. The specimen is divided into 4 portions; one is kept as blank, and to the other 3 are added 0, 20 and 40 [mu]g. of nicotinic acid. The solns., which must be protected throughout from the light, are warmed with CNBr, cooled, treated with p-aminoacetophenone, allowed to stand and acidified, and the 3 colour intensities measured in a Pulfrich photometer with S 47 filter, comparing with the blank to which no CNBr has been added. For any given specimen the depth of color varies with the pH, with the conc. of salts, and possibly with other factors, but the 3 readings always lie on a straight line and by extrapolation to zero the content of nicotinic acid can be accurately detd. Duplicates agree well, within an error of about [plus or minus] 10%, and added nicotinic acid or amide is quantitatively recovered. In humans the output varied according to the intake, and rose after test doses; and lowered values were found in pellagra, and with anorexia. The normal range of values was usually from 3-5 mg. per day; but further detailed work is still needed to establish exact quantitative standards of normality. Guinea pigs or dogs deprived of nicotinic acid showed a progressive fall in the excretion as the symptoms of deficiency developed and ultimately, a zero. In rats, the output was increased with a high intake of the vit., but the continued excretion on a deficient diet suggests some power of synthesis by the rat. Vit. B6 does not interfere.