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Studies of Potassium Depletion Using Direct Measurements of Total-Body Potassium

University Hospital, Boston Veterans Administration Hospital and Boston University School of Medicine, Boston University Medical Center, Boston, Massachusetts

Correspondence: For reprints contact: Ian B. Tyson, Dept. of Radiology, University of Wisconsin Medical Center, 1300 University Ave., Madison, Wisconsin 53706.

ABSTRACT

Replicate measurements of ⁴⁰K counting rate in 30 normal subjects over the intervals of days to 3 years showed a variation of less than 2.2% of the mean counting rate in a given individual in the group studied. With ⁴²K calibration for absolute measurements of body potassium, an overall counting error in a given measurement was ±2.3% while in 11 determinations in one subject the body potassium was 3,127 ± 27.4 mEq, a standard error of ±4.8% of the mean at the 99% confidence limits.

Body-potassium estimations within ±5% of the actual value could be obtained without ⁴²K calibration by using a body thickness factor derived from height and weight.

Body potassium related to the difference between tritium and ¹⁴C-inulin spaces was found to be 152.5 ± 11.5 (s.d.) mEq K⁺/liter of intracellular water in 25 normal controls. Using radiosulfate dilution as the index for extracellular fluid volume, the value for intracellular potassium was 122.0 ± 21.7 (s.d.) in 13 normal subjects.

Potassium depletion in relation to these body-fluid parameters was noted with normal serum potassium values in patients with hypertension, endocrine disorders or other diseases. Two patients with untreated essential hypertension had normal body-potassium values and serum potassium concentrations.

FOOTNOTES

^* Present address: See above.