What tests are required before initiating lithium (lithium carbonate) therapy?

Required Tests Before Starting Lithium Therapy

Before initiating lithium therapy, baseline assessments must include renal function tests, thyroid function tests, electrolyte tests (particularly calcium), urinalysis, and a pregnancy test for females of reproductive age. 1

Comprehensive Pre-Lithium Testing Protocol

Essential Laboratory Tests

• Renal Function Tests:

  • Complete blood count
  • Blood urea nitrogen (BUN)
  • Creatinine
  • Estimated glomerular filtration rate (eGFR) 1

• Thyroid Function Tests:

  • Thyroid stimulating hormone (TSH)
  • Free T4 1

• Electrolyte Panel:

  • Serum calcium (particularly important due to lithium's effects on parathyroid function) 1, 2
  • Sodium (relevant for lithium clearance)

• Other Tests:

  • Urinalysis (to assess baseline renal function) 1
  • Pregnancy test for women of reproductive age 1

Medical Evaluation

A complete medical history and physical examination should be performed to rule out any conditions that might affect lithium metabolism or increase risk of toxicity 3. This is particularly important because:

• Lithium is primarily excreted by the kidneys, making renal function assessment critical 1
• Patients with renal failure are at high risk for lithium accumulation and toxicity 4
• Treatment with thiazide diuretics is a contraindication due to increased risk of lithium toxicity 4

Rationale for Testing Requirements

1. Renal Function: Lithium is eliminated primarily through the kidneys. Impaired renal function can lead to lithium accumulation and toxicity. The FDA warns that "lithium toxicity is closely related to serum lithium levels, and can occur at doses close to therapeutic levels" 5.

2. Thyroid Function: Lithium significantly increases the risk of clinical hypothyroidism (odds ratio 5.78) 2. Baseline thyroid function tests are essential to detect pre-existing conditions and monitor changes during treatment.

3. Calcium Levels: Lithium treatment is associated with increased blood calcium (+0.09 mmol/L) and parathyroid hormone (+7.32 pg/mL) 2. The high prevalence of hyperparathyroidism necessitates calcium screening before and during treatment 2.

4. Pregnancy Testing: Lithium may cause fetal harm if administered during pregnancy, particularly in the first trimester 1, 4.

Monitoring Protocol After Initiation

Once lithium therapy begins, regular monitoring is essential:

• Serum Lithium Levels:

  • Twice weekly until stabilized in the acute phase 1
  • Every 2-3 months during maintenance phase 1
  • Samples should be drawn 12 hours after the last dose 1, 5
  • Target therapeutic range: 0.6-1.2 mEq/L for maintenance 5

• Ongoing Assessments:

  • Renal function, thyroid function, and urinalysis every 3-6 months 1
  • Annual assessment of urinary concentrating capacity after 5 years of treatment 6

Common Pitfalls to Avoid

1. Inadequate Monitoring: Some practitioners fail to check lithium levels as frequently as recommended (25% of GPs and 11% of psychiatrists), and monitoring of creatinine and TSH is even less consistent 7.

2. Failure to Recognize Drug Interactions: Thiazide diuretics can increase lithium levels and toxicity risk 4.

3. Overlooking Calcium Monitoring: Despite consistent findings of hyperparathyroidism risk, calcium monitoring is often neglected 2.

4. Improper Timing of Blood Samples: Lithium levels should be measured 12 hours after the last dose when concentrations are relatively stable 5.

5. Relying Solely on Serum Levels: The FDA emphasizes that "total reliance must not be placed on serum levels alone. Accurate patient evaluation requires both clinical and laboratory analysis" 5.

By following this comprehensive pre-lithium testing protocol, clinicians can minimize risks and establish appropriate baseline values for ongoing monitoring during lithium therapy.