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General / Metabolic

Electrolyte Disorders: Sodium, Potassium, and Calcium

Quick-reference causes and key features for the three electrolyte disturbances you will see most.

Sodium

Hyponatremia is classified by volume status: hypovolemic (GI or renal losses), euvolemic (SIADH, hypothyroidism, adrenal insufficiency), or hypervolemic (heart failure, cirrhosis). Symptoms range from mild (nausea, headache) to severe (seizures, coma), depending on both severity and how quickly it developed. If glucose is significantly elevated, use the corrected sodium calculator first to rule out pseudohyponatremia.

Hypernatremia is usually a free water deficit — poor intake, diabetes insipidus, or osmotic diuresis. Symptoms include thirst, confusion, and seizures.

Potassium

Hyperkalemia causes include renal failure, ACEi/ARB use, potassium-sparing diuretics, acidosis (shifts potassium out of cells), and tissue breakdown (rhabdomyolysis, tumor lysis). See the full Hyperkalemia Management Algorithm for treatment detail.

Hypokalemia causes include GI losses (vomiting, diarrhea), diuretics, insulin or beta-agonist use (shifts potassium into cells), and alkalosis.

Calcium

Hypercalcemia is most often caused by primary hyperparathyroidism in outpatients, and malignancy (via PTHrP or bone metastases) in inpatients. Remember it with "stones, bones, groans, and psychiatric overtones."

Hypocalcemia causes include hypoparathyroidism, vitamin D deficiency, pancreatitis, and massive transfusion (citrate binds calcium). Look for tetany, Chvostek's and Trousseau's signs, and a prolonged QT. Use the corrected calcium calculator to adjust for albumin before interpreting a low result.

Related Topics

Frequently Asked Questions

Why does the rate of sodium change matter, not just the level?

Brain cells adapt to chronic sodium changes over time. Rapid correction of chronic hyponatremia can cause osmotic demyelination syndrome, which is why correction rate is capped even when the number looks similarly abnormal to an acute case.

Does acidosis cause high or low potassium?

Acidosis typically shifts potassium out of cells into the blood, raising serum potassium even if total body potassium is normal or low — correcting the acidosis can unmask a true deficit.

Why correct calcium for albumin?

About 40% of calcium is protein-bound, mostly to albumin. Low albumin lowers total calcium readings without necessarily reflecting true free (ionized) calcium status.