Correlation Between First Morning Single Void and 24-Hour Urines: The Reliability to Quantify Niacin Status

BACKGROUND The current common practice when using urine as a biomarker for vitamin excretion is to use a 24-hour sample for analysis. Due to the difficulty involved in this process, we attempted to find an alternative solution through the use of a single first morning void. The aim of our study was to investigate if there is a correlation between the first morning single void and the 24-hour collections of urines for the urine metabolite of niacin, N-1-methylnicotinamide (N1MN), and to test the reliability of utilizing a method using first morning single void collections corrected with the concentration of urine creatinine. MATERIAL AND METHODS All urine samples were collected from 30 healthy adult volunteers over the age of 18 years: 20 females and 10 males. Samples were collected after discarding the first morning urine and collecting every other urine voided during the next 24 hours including the first morning urine of the day after in 2 separate vessels. We analyzed the concentration of N1MN by high performance liquid chromatography and the concentration of creatinine by a commercial kit by spectrophotometry. The B3 excretion was expressed as the ratio of N1MN to creatinine. RESULTS We found a significant correlation between the ratios of first morning single void and 24-hour urines. When comparing males and females, the ratio demonstrated a significant correlation as well. CONCLUSIONS Our results demonstrated that it is possible to substitute a 24-hour collection with a first morning single void urine for the estimation of N1MN excretion.