Exchangeable Body Potassium Measured from Parotid Saliva ∗

Abstract

Summary

Exchangeable body potassium (K_e) is measured from specific activity of parotid saliva (cannulated). Evidence for the suitability of parotid saliva as a substitute for urine in measuring exchangeable potassium (K_e) is supported by our results. The K-specific activity in plasma, urine, and saliva is practically identical 24, 30, and 36 hours after ⁴²K ingestion (see Pair-comparison t test in Table I). Ten to 15 min after intravenous ⁴²K injection, K-specific activity of urine and parotid saliva is far above plasma. Subsequently K-specific activity decreases rapidly and in a similar fashion in urine and saliva. At the seventh hour, K-specific activity approaches the same value in plasma, urine, and saliva. A high degree of correlation is found between simultaneously determined K_e from urinary and parotid saliva specimens 30 hours after ⁴²K ingestion (K_e saliva = 0.9989 · K_e urine + 2.4, r = 0.9768). The K_e may thus safely be determined from parotid saliva if no urinary specimens can be obtained or if important urinary tract obstruction is suspected.