When do you order calcium ionized (Ca2+) in patients?

When to Order Ionized Calcium Testing

Ionized calcium testing should be ordered during massive transfusion, in trauma patients, and in critically ill patients with suspected hypocalcemia, as it is essential for coagulation, cardiac function, and vascular tone. 1

Primary Indications for Ionized Calcium Testing

Trauma and Massive Transfusion

• Monitor ionized calcium levels in all patients undergoing massive transfusion 1
• Order at admission for trauma patients, as low admission levels predict mortality and need for multiple transfusions 1
• Monitor during transfusion of blood products, especially FFP and platelets, due to citrate-induced hypocalcemia 1
• Maintain levels >0.9 mmol/L during massive transfusion to support coagulation and cardiovascular function 1

Critical Illness with Specific Conditions

• Calcium channel blocker toxicity 1
• Hyperkalemia 1
• Hypermagnesemia 1
• Documented hypocalcemia with symptoms 1
• Cardiac arrest with any of the above conditions 1

Clinical Significance of Ionized Calcium

Physiological Importance

• Normal range: 1.1-1.3 mmol/L 1
• pH-dependent: 0.1 unit increase in pH decreases ionized calcium by ~0.05 mmol/L 1
• Essential for:
  • Formation and stabilization of fibrin polymerization sites
  • Platelet function
  • Cardiac contractility
  • Systemic vascular resistance 1

Clinical Impact of Abnormal Levels

• Hypocalcemia (ionized Ca²⁺ <0.9 mmol/L):
  • Associated with platelet dysfunction, decreased clot strength
  • Predicts mortality and need for multiple transfusions
  • Causes cardiac dysrhythmias when <0.8 mmol/L 1
  • Impairs cardiovascular function and drug action 2

Monitoring Considerations

Frequency of Testing

• At admission for trauma patients 1
• During massive transfusion: monitor with each blood gas analysis 1
• Follow-up testing based on clinical status and initial results

Testing Method

• Blood gas analyzers provide rapid measurement of ionized calcium 1
• Standard laboratory tests do not accurately reflect calcium's effect on coagulation (samples are citrated then recalcified) 1

Treatment Thresholds

• Severe hypocalcemia (ionized Ca²⁺ <0.8 mmol/L): Immediate correction recommended 1
• Moderate hypocalcemia (ionized Ca²⁺ 0.8-0.9 mmol/L): Correction recommended during massive transfusion 1
• Mild hypocalcemia (ionized Ca²⁺ >0.9 mmol/L): May not require treatment in asymptomatic patients 3

Common Pitfalls and Caveats

• Avoid routine measurement in all ICU patients without specific indications, as abnormal values are common and often normalize with resolution of the primary disease 4
• Remember that pH affects ionized calcium levels; alkalosis decreases ionized calcium 1
• Consider that hypocalcemia in critical illness may sometimes be protective, and correction without clear indication might be harmful 4
• Calcium chloride is preferred over calcium gluconate for rapid correction in critically ill patients, especially with liver dysfunction 1
• Extravasation of calcium solutions can cause severe tissue injury; central venous administration is preferred 1

By following these guidelines for ionized calcium testing, clinicians can appropriately monitor and manage calcium levels in patients who would benefit most from this assessment.