What labs are recommended before starting Lithium (lithium carbonate) therapy?

Baseline Laboratory Tests Before Starting Lithium

Before initiating lithium therapy, obtain complete blood count, thyroid function tests (TSH and free T4), renal function tests (BUN and creatinine), serum calcium, urinalysis, and pregnancy test in females of childbearing potential. 1, 2

Essential Baseline Laboratory Panel

The following tests are required before starting lithium:

Renal Function Assessment

• Blood urea nitrogen (BUN) and serum creatinine are mandatory to establish baseline kidney function, as lithium is almost exclusively excreted renally and can cause progressive renal impairment 1, 2, 3
• Urinalysis should be performed to detect pre-existing renal abnormalities 1
• Consider calculating absolute creatinine clearance (mL/min) using the patient's actual body surface area rather than normalized eGFR for more accurate lithium dosing 1

Thyroid Function Tests

• TSH and free thyroxine (free T4) must be measured before starting lithium, as lithium commonly causes thyroid dysfunction, particularly hypothyroidism 1, 2, 4
• Lithium increases the risk of hypothyroidism with a hazard ratio of 2.31, making baseline assessment critical 4

Hematologic Testing

• Complete blood cell count is recommended to establish baseline values 1, 2

Calcium and Parathyroid Assessment

• Serum calcium levels should be measured at baseline, as lithium is associated with hypercalcemia and increased risk of parathyroid dysfunction (HR 1.43) 1, 4

Pregnancy Testing

• Pregnancy test in female adolescents and women of childbearing potential is essential, as lithium crosses the placenta and passes into breast milk 1, 3

Critical Context from FDA Labeling

Facilities for prompt and accurate serum lithium determinations must be available before initiating therapy, as lithium toxicity is closely related to serum levels and can occur at doses close to therapeutic levels 5. This is a black box warning emphasizing that you cannot start lithium without the ability to monitor levels.

Evidence Quality and Nuances

The guideline recommendations 1, 2 are based on consensus from the American Academy of Child and Adolescent Psychiatry and align with FDA labeling requirements 5. While these guidelines were developed for adolescent populations, the baseline testing requirements apply universally to adult patients as well.

Research evidence demonstrates that adverse effects occur early in treatment, with women under 60 years at particularly high risk for renal and thyroid complications 4. A large cohort study of 6,659 patients found that while severe outcomes are rare (chronic kidney disease in only 0.6%), baseline testing remains essential for detecting pre-existing conditions and establishing monitoring parameters 6.

Common Pitfalls to Avoid

• Do not start lithium without baseline renal function tests, as patients with renal insufficiency require dose adjustments or may have contraindications to lithium use 1, 3
• Do not skip thyroid testing even in asymptomatic patients, as subclinical hypothyroidism may be present and lithium will exacerbate it 4, 7
• Do not forget calcium measurement, as hyperparathyroidism can develop and may be present at baseline in up to 25% of patients in some studies 8
• Ensure pregnancy testing is performed in all women of childbearing age, as lithium clearance increases 30-50% during pregnancy and the drug passes into breast milk 3