Equations for the prediction of normal values for exchangeable sodium, exchangeable potassium, extracellular fluid volume, and total body water.

Despite the valuable research information on body electrolytes and water that is gained from isotope dilution studies, these investigations have not become routine clinical procedure. This is partly due to the fact that normal ranges for exchangeable sodium (NaE), exchangeable potassium (KE), extracellular fluid volume (E.C.F.V.), and total body water (T.B.W.) are wide owing to great individual variations in body fat content, so that it is difficult to differentiate normal from disease states.1 2 Also, equations for the prediction of normal values at present available from the literature are based on limited numbers of subjects investigated from single laboratories.