In a patient with hypocalcemia (low ionized calcium) and hypokalemia (low potassium), which electrolyte abnormality should be corrected first?

Correct Potassium First, Then Calcium

In patients with concurrent hypokalemia and hypocalcemia, you must correct magnesium deficiency first if present, then address potassium before attempting to fully correct calcium, as hypokalemia cannot be adequately corrected in the presence of hypocalcemia, and hypocalcemia cannot be fully corrected without adequate magnesium. 1

The Critical Sequence: Magnesium → Potassium → Calcium

Step 1: Check and Correct Magnesium Immediately

• Measure serum magnesium immediately - hypomagnesemia is present in 28% of hypocalcemic ICU patients and prevents correction of both calcium and potassium 1
• Administer IV magnesium sulfate for replacement if hypomagnesemia is present, as hypocalcemia cannot be fully corrected without adequate magnesium 1
• This is the most commonly missed step and explains many cases of "refractory" hypocalcemia or hypokalemia 1

Step 2: Address Potassium Correction

• Once magnesium is repleted, focus on potassium correction as the priority 2
• Severe or symptomatic hypokalemia requires urgent treatment, particularly if ECG changes are present 2
• Administer oral or intravenous potassium replacement based on severity 2

Step 3: Approach Calcium Correction Cautiously

• For asymptomatic hypocalcemia, no immediate intervention is recommended 3
• Only treat calcium if the patient is symptomatic (paresthesias, Chvostek's/Trousseau's signs, tetany, seizures, or cardiac arrhythmias) 3, 1
• If symptomatic, administer calcium gluconate 50-100 mg/kg IV slowly with ECG monitoring 3

The Physiologic Rationale

• Hypokalemia and hypocalcemia frequently coexist because both depend on adequate magnesium for proper cellular handling 1
• Attempting to correct calcium before addressing magnesium and potassium will be ineffective and may waste time in critical situations 1
• The coexistence of these electrolyte abnormalities suggests an underlying process (renal losses, GI losses, or redistribution) that must be considered 2

Critical Pitfalls to Avoid

• Do not aggressively treat asymptomatic hypocalcemia - overcorrection can result in iatrogenic hypercalcemia, renal calculi, and renal failure 1
• In the context of hyperphosphatemia (such as tumor lysis syndrome), calcium administration increases the risk of calcium-phosphate precipitation in tissues and obstructive uropathy - exercise extreme caution and consider renal consultation 3
• Never mix sodium bicarbonate with calcium in the same IV line, as precipitation will occur 3, 1
• Standard coagulation tests may appear normal despite significant hypocalcemia-induced coagulopathy because laboratory samples are recalcified before analysis 1

Monitoring Strategy

• Monitor ionized calcium (not just corrected total calcium) every 4-6 hours initially until stable 1
• Continue monitoring potassium levels during replacement therapy 2
• Recheck magnesium after initial replacement to ensure adequacy 1
• ECG monitoring is essential during both potassium and calcium replacement 3, 1

Special Considerations

• If the patient has chronic kidney disease with PTH >300 pg/mL, active vitamin D sterols are indicated once acute management is complete 1
• In patients with 22q11.2 deletion syndrome, hypocalcemia can recur at any age during biological stress (surgery, infection, pregnancy) despite apparent childhood resolution 1
• Vitamin D deficiency (25-hydroxyvitamin D <30 ng/mL) should be addressed with supplementation once the acute phase is managed 1