When can I send a patient for a lithium level blood draw?

Timing for Lithium Level Blood Draw

For accurate lithium level monitoring, blood samples should be drawn 12 hours after the last dose for standard release formulations, or 24 hours after the last dose for once-daily extended-release formulations.

Rationale for Timing of Lithium Level Testing

Standard Release Formulations (Multiple Daily Doses)

• For patients taking lithium multiple times per day (standard release):
  • Draw blood 12 hours after the last dose 1
  • This timing provides relatively stable serum concentrations
  • Blood samples should be drawn immediately prior to the next scheduled dose 2

Extended-Release Formulations (Once Daily Dosing)

• For patients taking once-daily extended-release lithium:
  • Draw blood 24 hours after the last dose 3
  • The 24-hour level represents the true trough level for once-daily dosing
  • 12-hour levels are approximately 1.3 times higher than 24-hour levels with once-daily dosing 3

Therapeutic Ranges and Monitoring Frequency

Acute Phase Monitoring

• During acute treatment phase:
  • Monitor serum levels twice per week 2
  • Continue this frequency until serum level and clinical condition stabilize 2
  • Target therapeutic range: 1.0-1.5 mEq/L for acute mania 2

Maintenance Phase Monitoring

• During maintenance/long-term control:
  • Monitor serum levels at least every two months 2
  • Target therapeutic range: 0.6-1.2 mEq/L 2
  • Some experts recommend a narrower range of 0.6-0.8 mEq/L 4

Special Considerations

Elderly Patients

• Elderly patients often require reduced dosage 2
• They may exhibit toxicity at serum levels normally tolerated by other patients 2
• Consider maintaining lower therapeutic ranges for elderly patients 4

Sustained-Release Formulations

• With sustained-release preparations, consider keeping serum concentrations in the upper range (0.8-1.0 mmol/L) rather than 0.6-0.8 mmol/L used for standard formulations 4

Practical Tips for Accurate Monitoring

1. Standardize the timing of blood draws relative to last dose
2. Ensure consistent sampling time of day
3. Use the same laboratory for testing when possible
4. Maintain consistent tablet brand/formulation 5
5. Document time of last dose and time of blood draw

Common Pitfalls to Avoid

• Incorrect timing: Drawing blood at random times rather than at trough levels
• Failure to adjust for formulation: Not accounting for differences between standard and extended-release formulations
• Inconsistent monitoring: Not following recommended frequency based on treatment phase
• Overlooking clinical status: Relying solely on serum levels without clinical evaluation 2
• Inadequate documentation: Not recording time of last dose relative to blood draw

Remember that accurate lithium monitoring requires both clinical and laboratory analysis, and total reliance should not be placed on serum levels alone 2.