Laboratory Tests When Initiating Lithium Therapy
Before starting lithium and during the acute stabilization phase, you must order: serum lithium levels (twice weekly initially), serum creatinine/renal function tests, and thyroid-stimulating hormone (TSH), with lithium levels drawn as a trough 12 hours post-dose. 1
Pre-Treatment Baseline Laboratory Tests
Before initiating lithium therapy, establish baseline values for:
- Renal function (serum creatinine, eGFR) - Essential because lithium is almost exclusively excreted via the kidney, and renal insufficiency is considered a contraindication to lithium use 2, 3
- Thyroid function (TSH) - Required baseline since lithium can affect the thyroid gland 4
- Electrolytes - Important for assessing baseline status and future monitoring 5
Failing to establish baseline renal function before initiating lithium is a critical error that must be avoided 2.
Lithium Level Monitoring During Acute Phase
Initial Monitoring Frequency
- Check serum lithium concentrations twice per week during the acute phase until serum concentrations and clinical condition have stabilized 2, 1
- This intensive monitoring is necessary because lithium toxicity is closely related to serum lithium levels and can occur at doses close to therapeutic levels 1
Proper Timing of Blood Draws
- Draw blood samples 12 hours after the last dose (standardized 12-hour trough level) when lithium concentrations are relatively stable 1, 6
- For once-daily dosing regimens, the 24-hour trough should serve as the control value 3
- Blood sampling must occur at the same hour and be standardized with regard to dosage schedule to correctly monitor treatment 7
Target Therapeutic Range
- Target serum lithium levels of 0.6-1.2 mEq/L for maintenance therapy 1
- During acute mania treatment, levels of 1.0-1.5 mEq/L are typically effective 1
- Levels ≥1.5 mEq/L represent the lower limit of risk for intoxication 6
Ongoing Monitoring During Maintenance Therapy
Lithium Level Monitoring
- Check serum lithium levels at least every two months during uncomplicated maintenance therapy 1
- More frequent monitoring is required if symptoms of toxicity appear, regardless of the scheduled interval 2
Renal Function Monitoring
- Monitor renal function regularly throughout treatment, as lithium clearance decreases with aging and renal impairment increases toxicity risk 2, 3
- Temporarily suspend lithium during intercurrent illness, IV radiocontrast administration, bowel preparation, or prior to major surgery 5, 2
Thyroid Function Monitoring
- Check TSH at least twice yearly during maintenance therapy 4
Electrolyte Monitoring
- Monitor electrolytes regularly, especially potassium and magnesium, as correction of these is important if toxicity develops 5
Special Considerations Requiring More Frequent Monitoring
- Concurrent medications (NSAIDs, diuretics) that interact with lithium necessitate earlier and more frequent monitoring 2
- Elderly patients often require reduced dosages and may exhibit toxicity at levels ordinarily tolerated by younger patients 1
- Dehydration, medication interactions, or declining renal function warrant immediate reassessment 5
Critical Pitfalls to Avoid
- Never rely solely on serum levels alone - accurate patient evaluation requires both clinical assessment and laboratory analysis 1
- Do not overlook the need for more frequent monitoring if any symptoms of toxicity appear (tremor, nausea, diarrhea, polyuria-polydipsia) 5, 2
- Avoid concomitant NSAIDs which can increase lithium levels, and ensure adequate hydration especially during illness 5, 2
- Educate patients and caregivers about early signs of toxicity to allow for rapid intervention 5