How often should lithium assay be checked in patients on lithium therapy?

Lithium Level Monitoring Frequency

During acute stabilization, check serum lithium levels twice weekly until both levels and clinical condition stabilize; once stable on maintenance therapy, check levels every 2-3 months, with renal and thyroid function tests every 3-6 months. 1, 2

Acute Phase Monitoring

• Check serum lithium levels twice per week during the acute phase until both serum levels and clinical condition have stabilized 1, 2
• Blood samples must be drawn 8-12 hours after the previous dose when lithium concentrations are relatively stable 1, 2
• Continue this intensive monitoring schedule throughout the entire acute treatment period until therapeutic stability is achieved 2

Maintenance Phase Monitoring

Serum Lithium Levels

• For uncomplicated cases receiving maintenance therapy during remission, monitor serum lithium levels at least every 2 months 2
• The FDA label specifies "at least every two months" as the minimum standard for stable patients 2
• Recent evidence suggests that for patients who maintain lithium levels consistently within the 0.40-0.79 mmol/L range for 12 months, the testing interval could potentially be extended to 6 months (90% remain within target range at this interval) 3
• However, patients with levels in the 0.80-0.99 mmol/L range should continue 3-monthly testing due to higher risk (10%) of progressing to toxic levels 3

Renal and Thyroid Function

• Check renal function tests (BUN, creatinine), thyroid function tests (TSH, free T4), and urinalysis every 3-6 months 1
• Check serum calcium at least annually 1
• The American Academy of Child and Adolescent Psychiatry recommends this 3-6 month interval for ongoing monitoring of renal and thyroid function 1

Baseline Testing Requirements

Before initiating lithium therapy, obtain:

• Complete blood count 1
• Thyroid function tests (TSH, free T4) 1
• Renal function tests (BUN, creatinine) 1
• Serum calcium 1
• Urinalysis 1
• Pregnancy test in females of reproductive age 1

Special Circumstances Requiring Increased Monitoring

• Increase monitoring frequency during intercurrent illness 1
• Patients with reduced kidney function (GFR <60 mL/min/1.73 m²) require more frequent monitoring 4
• Elderly patients often require closer monitoring as they may exhibit toxicity at levels ordinarily tolerated by younger patients 2
• Patients abnormally sensitive to lithium may show toxic signs at serum levels of 1.0-1.5 mEq/L, necessitating more frequent checks 2

Critical Monitoring Pitfalls

• Total reliance must not be placed on serum levels alone—accurate patient evaluation requires both clinical and laboratory analysis 2
• Early signs of lithium toxicity (tremor, nausea, diarrhea, polyuria-polydipsia) warrant immediate testing regardless of scheduled monitoring intervals 1
• Lithium toxicity can occur at doses close to therapeutic levels, with toxicity beginning at 1.5 mEq/L and serious toxicity at >2.0 mEq/L 4
• National audits have shown that only 30% of patients meet NICE standards for lithium level monitoring and 50-55% meet standards for renal and thyroid monitoring, indicating widespread undermonitoring in clinical practice 5