Background:
(1) Since most potassium is intracellular, the total body exchangeable potassium correlates with the body cell mass.
(2) Since most sodium is extracellular, the total body exchangeable sodium correlates with extracellular mass.
ratio of total body exchangeable sodium to total body exchangeable potassium =
= (total body exchangeable sodium in mEq) / (total body exchangeable potassium in mEq)
NOTE: A discussion on the total body exchangeable sodium and potassium is given in the Chapter on endocrinology and metabolism.
Interpretation:
• Normal volunteers have a ratio of 0.98.
• Shizgal determined that a ratio > 1.22 defined malnutrition reliably.
Tellado-Rodriguez et al showed that death associated with malnutrition could be predicted from the ratio as:
X =
= (5.2 * (ratio)) – 11.8
probability of death =
= 1 / (1 + EXP((-1) * X))
