Hypokalcemia

Hypokalemia, sometimes spelled hypokalcemia in some sources, is a condition defined by a serum potassium concentration below 3.5 mmol/L. Potassium is essential for nerve conduction, muscle contraction, and heart rhythm. Most cases are asymptomatic or mild, but lower levels can affect multiple body systems, especially the muscles and the heart.

Common causes include losses from the body or shifts of potassium into cells. Renal potassium loss is frequent, seen with the use of loop or thiazide diuretics or with mineralocorticoid excess. Gastrointestinal losses from vomiting or diarrhea can contribute. Transcellular shifts occur with metabolic alkalosis, insulin use, or beta-adrenergic stimulation. In some people, inherited tubulopathies (such as Bartter or Gitelman syndrome) or magnesium deficiency can predispose to hypokalemia.

Symptoms range from none to significant weakness, cramps, fatigue, and constipation. Cardiac effects may include palpitations or arrhythmias; in severe cases, muscle weakness or paralysis can involve respiratory muscles. Electrocardiogram changes commonly seen with hypokalemia include flattened or inverted T waves, prominent U waves, ST depression, and QT interval prolongation.

Diagnosis relies on a blood test to measure serum potassium and on assessment of possible causes. Urinary potassium excretion helps distinguish renal from extrarenal losses. Additional tests may check magnesium status, acid-base balance, and monitor for ECG abnormalities.

Treatment depends on severity and symptoms. Mild cases may be treated with oral potassium chloride supplementation and addressing the underlying cause. Moderate to severe hypokalemia or symptoms often require intravenous potassium, with careful rate limits and continuous monitoring. Correcting any coexisting magnesium deficiency is important, and ongoing management may involve adjusting medications, dietary potassium, and prevention strategies in at-risk patients.