Total Body Protein (TBP)

The Total Body Protein (TBP) is a body compositoin method which measures the amount of nitrogen in the body, which is a direct indicator of total body protein (TBP). The test involves irradiation of the subject with neutrons, which causes them to give off characteristic gamma rays.

purpose: to measure total body protein.

equipment required: Prompt Gamma Activation Analyzer.

procedure: Before the scan begins, the subject undergoes measures of chest, arm, waist, and leg widths and thickness. These measurements are used to adjust the nitrogen scan data for a subject's size and shape. The subject then lies fairly still in the supine position as three separate body sections (legs, waist, chest) are measured for 10 minutes each. The scan involves irradiation of the subject with neutrons, and cause them to give off characteristic gamma rays. The gamma rays are collected from detectors placed on either side of the subject, and analyzed using conventional spectroscopy.

results: Total protein can be estimated from the ratio of nitrogen to hydrogen counts. Nitrogen and protein are closely linked with each other because of a stable chemical combination (protein is 16% nitrogen) and because over 98% of the total body nitrogen is in the form of protein.

advantages: When this measurement is combined with measurements from the Total Body Potassium Counter, it is possible to determine total organ and muscle mass.

disadvantages: the required instrument is very expensive to install and has limited availability.

comments: The system is called a prompt gamma system as the gammas are produced immediately, and stop appearing as soon as the neutron source is removed.

use: Prompt Gamma Activation Analysis is the gold-standard method for measuring the amount of nitrogen in the body, which in turn is a direct indicator of total body protein (TBP).

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