Laboratory measurement of sodium and potassium.

This paper continues our series on pathology testing. The urea and electrolyte (U&E) blood test, which includes the measurement of sodium and potassium concentration in blood plasma, is the most frequently requested chemical test in clinical practice. The precautions to be taken when sampling blood for this test are described. This is followed by a brief review of conditions associated with abnormalities in serum sodium and potassium concentrations and the effects of these changes. It is particularly important that the signs and symptoms of changes in plasma potassium concentration particularly are recognised and treated quickly, as these are potentially life-threatening.