Simultaneous measurement of total exchangeable potassium and sodium using 43K and 24Na

Abstract

The simultaneous measurement of total exchangeable potassium and total exchangeable sodium is described using 43K and 24Na in 67 patients. Smaller doses of radioisotope were used than previously reported, but despite this a 44-hr mixing period was achieved for potassium. The coefficients of variation for duplicate estimations of radioactivity (potassium. 2.5%, sodium 1.51%) or for exchangeable electrolyte determinations (K e at 44 hr 1.93%; Na e at 24 hr 1.77%) appear comparable to or better than the results of previous studies. The whole-body radiation dose to the patient was estimated at 17 mrad. Eight patients had independent measurements of body potassium ( 40K), and these were in close agreement with the K e value. It is felt that 43K should replace 42K for the measurement of total exchangeable potassium in man.