Total Body Potassium: A Reference Measurement for the Body Cell Mass

Abstract

The quantitative in vivo measurement of radioactivity in the human body began with the development of scintillation detectors in the 1940s. These detectors were incorporated into first-generation whole-body counters in response to the health concern that internal contamination would result from work with radioactive materials. Accidental exposures turned out to be rare. These systems were at nuclear facilities involved both in basic research and in development of applications (e.g., isotopes for nuclear medicine). It was quickly recognized that trace amounts of radioactive-labeled compounds could be detected in an organ if a sufficient concentration were present. The origins of nuclear medicine can be traced, in part, to early studies using whole-body counters. During routine monitoring of nuclear workers, a persistent high-energy peak in the background spectrum was often observed. Several research groups can be credited for recognizing that this “background signal” was the body’s natural content of the potassium radiotracer ⁴⁰K. Kulwich (1958) noted the relation of ⁴⁰K content to fat-free mass (FFM), quickly followed by Anderson and Langham (1959), to offer the earliest insights into body potassium as an index of body composition in humans. Cadaver analyses by Forbes and Lewis (1956) enabled the subsequent use of body potassium as an indirect marker for estimating body fat mass. More than 180 whole-body counters were operational worldwide by the early 1970s, with more than two thirds of these instruments used to measure body potassium in humans (International Atomic Energy Agency 1970). In the last 15 years, multidetector whole-body counting instruments have been built in body composition laboratories at three U.S. Department of Agriculture (USDA) human nutrition research centers (Grand Forks, ND, Boston, MA and Houston, TX), a clinical research/medical physics consortium (New York City/Upton, NY), and a primary care hospital/medical school (Galveston, TX).