Assessment of protein nutrition in surgical patients--the value of anthropometrics

In order to evaluate the reliability of anthropometry in assessing protein stores we have compared, in 10 normal adults and 82 surgical patients with varying degrees of weight loss, measurements of weight/height, arm circumference, arm muscle circumference, and arm muscle area with direct measurements of body nitrogen using in vivo neutron activation analysis. Anthropometry is reliable for the assessment of protein nutrition in groups of patients (for 100 patients 95% confidence limits are +/- 30 g nitrogen) but the magnitude of variance shown makes it inappropriate for assessing the individual as a single measurement (95% confidence limits are +/- 300 g nitrogen). Repeat measurements were made after 2 weeks on 35 patients and there was no correlation between changes in body nitrogen and changes in the anthropometric measurements. Anthropometry is not reliable in following changes in body nitrogen in individual patients over short periods of time.