Pre-Lithium Laboratory Testing
Before initiating lithium therapy, you must obtain baseline complete blood count, thyroid function tests (TSH), renal function tests (creatinine, BUN), serum calcium, urinalysis, and a pregnancy test in females of reproductive age. 1, 2
Essential Baseline Laboratory Tests
The following tests are required before starting lithium:
Renal function assessment: Serum creatinine and blood urea nitrogen (BUN) to establish baseline kidney function, as lithium is renally excreted and can cause nephropathy 1, 2, 3
Thyroid function tests: TSH (thyroid-stimulating hormone) to detect pre-existing thyroid dysfunction, as lithium commonly causes hypothyroidism 1, 2, 3, 4
Serum calcium: Baseline calcium level to screen for pre-existing parathyroid abnormalities, as lithium is associated with hypercalcemia and hyperparathyroidism 1, 2, 3, 5
Complete blood count (CBC): To establish baseline hematologic parameters 1, 2
Urinalysis: To assess baseline renal function and detect any pre-existing kidney disease 1, 2
Pregnancy test: Mandatory in all females of reproductive age due to teratogenic risks 1, 2
Critical Safety Considerations
Facilities for prompt and accurate serum lithium determinations must be available before initiating therapy, as lithium toxicity can occur at doses close to therapeutic levels. 6 This is an FDA-mandated warning that emphasizes the narrow therapeutic window of lithium.
Rationale for Each Test
Renal Function
Lithium is almost exclusively excreted via the kidney as a free ion, and lithium clearance decreases with aging and renal insufficiency 7. Long-term lithium use is associated with increased risk of stage 3 chronic kidney disease (HR 1.93) 3. Baseline creatinine allows you to calculate estimated GFR, which is essential for dosing adjustments and monitoring.
Thyroid Function
Lithium causes hypothyroidism with a hazard ratio of 2.31 compared to non-lithium users 3. Women are at particularly high risk 3. Baseline TSH allows detection of pre-existing thyroid disease and provides a reference point for monitoring. After 4 months of lithium therapy, TSH typically increases and T4/T3 decrease, though clinical hypothyroidism may not develop immediately 4.
Serum Calcium and Parathyroid Function
Lithium increases the risk of hypercalcemia (HR 1.43) and can cause hyperparathyroidism 3, 5. Baseline calcium measurement is essential to detect pre-existing parathyroid dysfunction.
Pregnancy Testing
This is non-negotiable in females of reproductive age due to lithium's teratogenic effects, particularly cardiac malformations 2.
Common Pitfalls to Avoid
Do not start lithium without ensuring access to lithium level monitoring facilities - this is an FDA black box consideration and critical for safety 6
Do not skip the pregnancy test in any female of reproductive age, regardless of reported sexual activity 1, 2
Do not use estimated GFR normalized to body surface area (mL/min/1.73 m²) for lithium dosing - you need absolute clearance (mL/min) by back-calculating using the patient's actual body surface area, especially in patients significantly larger or smaller than average 8
Women under 60 years and patients with higher lithium concentrations are at greatest risk for adverse effects - consider this when establishing monitoring frequency 3