Perinatal nitrogen accretion in muscles and fingernails

Paired triceps muscle and fingernail samples were obtained at autopsy from 25 normally grown (NG) and 16 intrauterine growth-retarded (IGR) neonates who died within 28 days of birth. Gestational ages ranged from 21--46 weeks and birthweights ranged from 425--3750 g. Muscle samples were desiccated, defatted and ground to powder. Nitrogen content of muscle and fingernail were determined by a modified micro-Kjeldahl technique. Muscle nitrogen (MN) content averaged 12.1 +/- 1.89 g/100 g fat-free dry solids (FFDS) (mean +/- SD) and was similar for NG and IGR neonates and, within these two groups, for premature and mature babies. Fingernail nitrogen (FN) content averaged 13.8 +/- 0.95 g/100 g and no variations with duration and quality of intrauterine growth were identified. Fingernail nitrogen content correlated linearly with muscle nitrogen content in both NG (n = 0.48, P less than 0.002) and IGR (n = 0.67, P less than 0.005) neonates. The regression equation for the entire study population was: FN = 0.31MN + 9.96, Syx = +/- 0.778, r = 0.59, P less than 0.001. These data suggest the possibility of using simple, noninvasive fingernail "biopsies" to monitor protein economy and quality of perinatal growth.