Potassium is one of the body's major ions. Nearly 98% of the body's potassium is intracellular. The ratio of intracellular to extracellular potassium is important in determining the cellular membrane potential. Small changes in the extracellular potassium level can have profound effects on the function of the cardiovascular and neuromuscular systems. [1, 2, 3]
The kidney determines potassium homeostasis, and excess potassium is excreted in the urine.
The reference range for serum potassium level is 3.5-5 mEq/L, with total body potassium stores of approximately 50 mEq/kg (ie, approximately 3500 mEq in a 70-kg person).
Hypokalemia is defined as a potassium level less than 3.5 mEq/L.
Moderate hypokalemia is a serum level of 2.5-3 mEq/L.
Severe hypokalemia is defined as a level less than 2.5 mEq/L.
Hypokalemia may result from conditions as varied as renal or GI losses, inadequate diet, transcellular shift (movement of potassium from serum into cells), and medications.
As many as 20% of hospitalized patients are hypokalemic; however, hypokalemia is clinically significant in only about 4-5% of these patients. Severe hypokalemia is relatively uncommon.
Up to 14% of outpatients who undergo laboratory testing are found to be mildly hypokalemic.
Approximately 80% of patients who are receiving diuretics become hypokalemic.
In an Italian study, Giordano et al found that of 7941 emergency department patients, 13.7% of them had an electrolyte imbalance, with hyponatremia being the most common (44%) and hypokalemia being the next most frequent (39%). The investigators also found that 98% of patients with an electrolyte imbalance had an associated systemic disease. 
Incidence is equal in males and females.
Hypokalemia usually resolves with appropriate therapy. A study by Krogager et al indicated that patients with hypertension who have a potassium level outside of the 4.1-4.7 mmol/L range, including those who are hypokalemic or hyperkalemic, have an increased mortality risk. For patients with hypokalemia, the 90-day mortality rate was 4.5%, compared with 1.5% for the 4.1-4.7 mmol/L range. 
Diet modification is recommended for those patients who are predisposed to hypokalemia. Increase intake of bananas, tomatoes, oranges, and peaches because they are high in potassium.
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