What labs should be ordered for routine monitoring of a patient on lithium therapy?

Routine Laboratory Monitoring for Lithium Therapy

For patients on maintenance lithium therapy, monitor serum lithium levels, renal function tests (BUN and creatinine), thyroid function tests (TSH), and urinalysis every 3-6 months, with serum calcium checked at least annually. 1

Baseline Testing Before Initiating Lithium

Before starting lithium, obtain the following laboratory tests:

• Complete blood count (CBC) 1
• Thyroid function tests: TSH and free T4 1
• Renal function tests: Blood urea nitrogen (BUN) and creatinine 1
• Serum calcium 1
• Urinalysis 1
• Pregnancy test in females of reproductive age 1

This comprehensive baseline assessment identifies pre-existing conditions that could be contraindicated or require closer monitoring during lithium therapy.

Serum Lithium Level Monitoring

During Acute Stabilization Phase

• Check serum lithium levels twice weekly until both serum levels and clinical condition stabilize 1, 2
• Blood samples must be drawn 8-12 hours after the previous dose when concentrations are relatively stable 2
• Target therapeutic range during acute mania: 1.0-1.5 mEq/L 2

During Maintenance Phase

• Check serum lithium levels every 2 months minimum in uncomplicated cases 2
• Target therapeutic range for long-term control: 0.6-1.2 mEq/L 2
• Note that research shows only 50.7% of lithium levels fall within recommended ranges in real-world practice, with 42.4% below therapeutic minimum 3

Critical caveat: Total reliance must not be placed on serum levels alone—accurate patient evaluation requires both clinical and laboratory analysis. 2

Renal Function Monitoring

• Monitor BUN, creatinine, and urinalysis every 3-6 months during stable maintenance therapy 1
• Increase monitoring frequency during intercurrent illness 1
• Lithium is associated with increased risk of chronic kidney disease (hazard ratio 1.93), making regular renal monitoring essential 4
• Temporarily discontinue lithium during serious intercurrent illness that increases acute kidney injury risk, especially in patients with GFR <60 mL/min/1.73 m² 1

Thyroid Function Monitoring

• Monitor TSH (and free T4 if indicated) every 3-6 months 1
• Subclinical hypothyroidism is a common adverse effect requiring regular surveillance 1
• Hypothyroidism occurs in 8-20% of lithium-treated patients, more frequently in women and those with pre-existing thyroid autoimmunity 5
• Pre-existing thyroid disorders do not necessarily contraindicate lithium, but require careful monitoring with supplemental thyroid treatment if hypothyroidism develops 2

Serum Calcium Monitoring

• Check serum calcium at least annually (periodically) 1
• Lithium stimulates parathyroid cell proliferation, resulting in 4-6 fold higher risk of primary hyperparathyroidism compared to the general population 5
• Monitor for hypercalcemia, which may present with a phenotype mimicking hypercalcemia-hypocalciuria syndrome 5

Electrolyte Monitoring

While not explicitly detailed in lithium-specific guidelines, monitor:

• Serum sodium: Lithium decreases sodium reabsorption by renal tubules, potentially leading to sodium depletion 2
• Patients must maintain normal diet including salt and adequate fluid intake (2500-3000 mL) during initial stabilization 2
• Supplemental fluid and salt should be administered if protracted sweating or diarrhea occurs 2

Monitoring Frequency Adjustments

Increase monitoring frequency in these situations:

• During intercurrent illness 1
• When initiating or discontinuing NSAIDs (which can significantly increase lithium levels) 2
• When starting diuretics or ACE inhibitors (which reduce renal clearance of lithium) 2
• Prior to IV radiocontrast administration, bowel preparation, or major surgery (temporarily suspend lithium) 6, 4
• In elderly patients who often exhibit toxicity at levels ordinarily tolerated by others 2

Clinical Monitoring for Toxicity

Educate patients to immediately report early signs of lithium toxicity:

• Tremor 1, 6
• Nausea and diarrhea 1, 6
• Polyuria-polydipsia 1, 6
• Vomiting, mild ataxia, drowsiness, or muscular weakness 2

These symptoms warrant immediate lithium level testing and clinical evaluation. 2

Common Monitoring Pitfalls

• Avoid drawing lithium levels within 8-12 hours of the last dose, as this will not reflect trough levels 2
• Do not rely solely on serum lithium levels—clinical assessment is equally important 2
• Real-world audits show only 30% of patients meet NICE standards for lithium level monitoring frequency, 55% for renal monitoring, and 50% for thyroid monitoring 7
• NSAIDs are contraindicated in lithium-treated patients due to significant drug interactions 1, 2