The prediction of body potassium in the elderly.

Whilst there are many regression formulae in the literature from which a predicted or expected value of body potassium can be calculated, different formulae give widely differing results. Several of these algorithms have been developed by estimating body potassium from exchangeable measurements which are not valid in most clinical situations. Those derived from studies of direct body-potassium measurement from whole-body counting have included few females or older persons--the very group likely to suffer disease-produced changes in potassium homeostasis. Eleven male and 11 female carefully screened healthy adults (mean agd 75, range 65-90 years) have been used to develop new formulae. It is shown that within this age range body potassium can be predicted from body weight to within +/- 20.4% in males and +/- 15.1% in females. These new relationships should be used in clinical practice for elderly patients.