INVIVO MEASUREMENTS OF BODY PROTEIN BASED ON THE DETERMINATION OF NITROGEN BY PROMPT GAMMA-ANALYSIS

Measurement of nitrogen in the human body gives a measure of total protein in the body. Nitrogen (N) may be measured in vivo by a nuclear technique in which the characteristic nitrogen γ rays emitted after capture of neutrons are detected and counted. The accuracy (as determined by comparison of the measurement of nitrogen in a pig by nuclear and chemical methods) is better than 10%. The reproducibility is <6%. The radiation dose is about 5 millirads. This method had been used with 43 patients and 23 normal volunteers and the results are reported. The data are presented in the form of total N content, percentage N by weight, and as a comparison of N and postassium (K) in the body. It is found that the mean percentage on N in the normal males is 2.5%, giving a value of 1.75 kg in the 70-kg standard man. The mean percentage values are not greatly different between normal volunteers and malnourished patients. Taking all subjects, N/K ratios ranged from 7.5 to 20 g/g. Thus K cannot be used as a predictor of N. Nitrogen content of normal correlates well (r=0.68) with height squared; for malnourished patients there is again a good correlation (r=0.81) but the regression line for patients is approximately 34% below that for the volunteers consistent with their depleted state.