Absolute measurement of total body calcium (bone mass) in vivo.

Abstract

Abstract Using total body neutron activation analysis (TBNA) and total body counting, a technique has been established to quantitate body calcium in grams with an estimated accuracy of 5.2 per cent (see below). Five cadavers of various body size were activated and counted to establish the ratio of their induced 49 Ca activity to a fixed calcium standard, activated and counted under identical conditions. The cadaver skeletons were then ashed and chemically analyzed to establish the specific activity; i.e., the 49 Ca activity induced per gram of skeletal calcium. Variations in specific activity between cadavers were linearly related to body weight divided by height (kilogram per meter). The TBNA results from subjects of various sizes measured in vivo could then be converted to grams of calcium using the cadavers as comparison standards. In 8 normal men, total body calcium ranged from 933 to 1,361 Gm., average 1,093 Gm. Data for body calcium from cadaver analyses from the literature plus the present results were inspected. The relationship between skeletal calcium and skeletal length suggests that total body calcium increases as 15 the cube of skeletal length. Applying this relationship to normal men measured by TBNA, the expression y=0.203 x 3 was derived where y=calcium in grams and x=height in meters. In 5 patients with known osteopenia from various causes, bone mass was shown to be reduced 23 to 35 per cent below the expected normal.