Clinical and Interpretive

Measurement of potassium is useful in the evaluation of electrolyte balance, cardiac arrhythmia, muscular weakness, hepatic encephalopathy, and renal failure. Potassium should be monitored during treatment of many conditions but especially in diabetic ketoacidosis and any intravenous therapy for fluid replacement.

Potassium is the major cation of the intracellular fluid. Disturbance of potassium homeostasis has serious consequences. Decreases in extracellular potassium are characterized by muscle weakness, irritability, and eventual paralysis. Cardiac effects include tachycardia, other cardiac conduction abnormalities that are apparent by electrocardiographic examination, and eventual cardiac arrest. Hypokalemia (low potassium) is common in vomiting, diarrhea, alcoholism, and folic acid deficiency. Additionally, >90% of hypertensive patients with aldosteronism have hypokalemia. Potassium levels <3.0 mmol/L are associated with marked neuromuscular symptoms and are evidence of a critical degree of intracellular depletion. Potassium levels <2.5 mmol/L are potentially life-threatening. Abnormally high extracellular potassium levels produce symptoms of mental confusion; weakness, numbness and tingling of the extremities; weakness of the respiratory muscles; flaccid paralysis of the extremities; slowed heart rate; and eventually peripheral vascular collapse and cardiac arrest. Hyperkalemia may be seen in end-stage renal failure, hemolysis, trauma, Addison’s disease, metabolic acidosis, acute starvation, dehydration, and with rapid potassium infusion. High potassium can be an acute medical emergency, particularly if the potassium increases over a short period of time. At values >6.0 mmol/L, symptoms are typically apparent. Potassium levels >6.0 mmol/L are potentially life-threatening. Levels >10.0 mmol/L are, in most cases, fatal.

It is important to remember that whole blood potassium values determined by direct potentiometry/ion-selective electrodes may be slightly higher in specimens with high protein and lipid concentrations than the corresponding serum specimen that is assayed by an indirect potentiometric method. The whole blood potassium values are the correct values.Ion-selective electrodes are selective for the ion in question but are not absolutely specific. Other monovalent cations may interfere but not in the physiologic range.