What causes hypokalemia (low potassium levels) and hypocalcemia (low calcium levels)?

Causes of Hypokalemia and Hypocalcemia

Hypokalemia and hypocalcemia can be caused by multiple conditions, with medication effects, gastrointestinal losses, and endocrine disorders being the most common etiologies that often require immediate attention to prevent serious cardiac and neuromuscular complications.

Common Causes of Hypokalemia

Medication-Induced

• Diuretics: Thiazides and loop diuretics are the most common causes of hypokalemia 1
• Laxatives: Chronic use causes intestinal potassium losses
• Glucocorticoids: Promote renal potassium excretion
• Insulin: Causes intracellular shift of potassium

Gastrointestinal Losses

• Vomiting/Diarrhea: Direct loss of potassium-containing fluids
• Short bowel syndrome: Impaired absorption with increased losses 1
• High-output ostomies: Jejunostomy or ileostomy can lead to significant potassium losses 1

Endocrine Disorders

• Hyperaldosteronism: Increases renal potassium excretion
• Cushing's syndrome: Excess cortisol promotes potassium excretion
• Magnesium deficiency: Causes refractory hypokalemia by affecting potassium channels 1, 2

Other Causes

• Renal tubular disorders: Impaired reabsorption of potassium
• Alkalosis: Causes intracellular shift of potassium 3
• Poor dietary intake: Rarely a sole cause but can contribute

Common Causes of Hypocalcemia

Medication-Induced

• Bisphosphonates: Inhibit bone resorption 4
• Anticonvulsants: Accelerate vitamin D metabolism
• Proton pump inhibitors: Reduce calcium absorption 4
• Cisplatin: Direct nephrotoxicity affecting calcium regulation 4
• Aminoglycosides: Can cause hypocalcemia through renal effects 4

Endocrine Disorders

• Hypoparathyroidism: Reduced PTH leads to decreased calcium 1
• Vitamin D deficiency: Impairs intestinal calcium absorption
• Hypomagnesemia: Impairs PTH secretion and action 1, 2
• Pseudohypoparathyroidism: End-organ resistance to PTH

Other Causes

• Chronic kidney disease: Reduced activation of vitamin D
• Acute pancreatitis: Calcium sequestration in pancreatic fat
• Critical illness: Multiple mechanisms including vitamin D deficiency
• Tumor lysis syndrome: Release of phosphate binds calcium

Combined Hypokalemia and Hypocalcemia

When both electrolyte abnormalities occur together, consider:

1. Hypomagnesemia: A key cause of both conditions 1, 2

   • Impairs PTH secretion causing hypocalcemia
   • Increases renal potassium wasting causing hypokalemia

2. Gastrointestinal disorders:

   • Short bowel syndrome 2
   • Malabsorption syndromes
   • Chronic diarrhea

3. Diuretic therapy:

   • Especially loop diuretics which increase urinary losses of both electrolytes 1

4. Renal tubular disorders:

   • Conditions affecting multiple electrolyte transport mechanisms

5. 22q11.2 deletion syndrome:

   • Causes hypoparathyroidism leading to hypocalcemia
   • May have associated hypokalemia 1

Clinical Pearls

• Always check magnesium levels when both hypokalemia and hypocalcemia are present, as hypomagnesemia is a common underlying cause 2
• Potassium replacement will be ineffective if underlying hypomagnesemia is not corrected 1, 2
• Biological stress (surgery, infection, childbirth) can worsen both conditions 1
• Carbonated beverages and alcohol can worsen hypocalcemia 1
• Patients on diuretics should be monitored for both electrolyte abnormalities 1

Treatment Approach

1. Identify and treat the underlying cause

2. For hypokalemia:

   • Oral supplementation for mild cases (K+ 3.0-3.5 mEq/L)
   • IV replacement for severe cases (K+ <3.0 mEq/L) or symptomatic patients 3
   • Target serum potassium in 4.0-5.0 mEq/L range 1

3. For hypocalcemia:

   • Calcium supplementation (oral or IV depending on severity)
   • Vitamin D supplementation as needed
   • Magnesium replacement if deficient 1

4. Monitor closely for rebound disturbances, especially with rapid correction