What blood tests should be done for a patient on Lithium (lithium carbonate) therapy, considering their kidney function, thyroid function, and potential comorbidities?

Complete Blood Test Panel for Lithium Monitoring

Baseline Testing (Before Starting Lithium)

Before initiating lithium therapy, obtain a comprehensive baseline laboratory panel including complete blood count, serum electrolytes (including calcium and magnesium), blood urea nitrogen, serum creatinine with estimated glomerular filtration rate (eGFR), thyroid function tests (TSH and free T4), fasting glucose or glycated hemoglobin (HbA1c), and urinalysis. 1, 2

• Complete blood count (CBC) with differential is required to document pre-existing cytopenias and identify contraindications such as severe baseline neutropenia or thrombocytopenia, particularly in patients with a history of blood disorders 1
• Serum creatinine and eGFR establish baseline renal function, as lithium causes progressive renal impairment in a substantial proportion of patients 2, 3, 4
• Thyroid function tests (TSH and free T4) are essential because lithium causes hypothyroidism in a significant percentage of patients, with women at particularly high risk 1, 3
• Serum electrolytes including calcium and magnesium identify baseline abnormalities and establish reference values for monitoring hypercalcemia and parathyroid dysfunction 1, 3
• Fasting glucose or HbA1c screens for diabetes, which affects lithium toxicity risk and monitoring frequency 1
• Urinalysis and assessment of urine concentrating ability (urine specific gravity or osmolality) evaluate baseline tubular function 2

Routine Maintenance Monitoring

During stable maintenance therapy, check serum lithium levels every 3 months, and monitor renal function (creatinine/eGFR), electrolytes, thyroid function (TSH, free T4), and calcium every 6 months. 1, 5

Lithium Levels

• Check serum lithium concentration every 3-6 months during stable maintenance therapy 1
• Draw levels 12 hours post-dose (trough level) for accurate interpretation 1
• Target therapeutic range is typically 0.6-1.2 mEq/L for maintenance (1.0-1.5 mEq/L for acute mania) 1

Renal Function Panel

• Monitor serum creatinine, eGFR, and electrolytes (sodium, potassium, calcium, magnesium) every 6 months 1, 2
• Progressive or sudden changes in renal function, even within normal range, require treatment reevaluation 2
• Up to 30% increase in creatinine from baseline is acceptable and does not require immediate intervention 1
• Creatinine increase >50% from baseline or >266 μmol/L triggers review of nephrotoxic medications and consideration of dose reduction 1
• Creatinine increase >100% from baseline or >310 μmol/L requires lithium discontinuation 1

Thyroid Function

• Check TSH and free T4 every 6-12 months 1, 5
• Women and younger patients (<60 years) are at higher risk for thyroid dysfunction 3
• Hypothyroidism develops in approximately 20-30% of patients on long-term lithium 3, 6

Calcium and Parathyroid Function

• Monitor serum calcium (total and ionized) every 6-12 months 1, 3
• Consider parathyroid hormone (PTH) levels if calcium is elevated, as hypercalcemia occurs in approximately 25% of long-term lithium patients 3, 6

Additional Annual Tests

• Weight and blood pressure annually 1
• Complete blood count annually to monitor for cytopenias 1

Intensified Monitoring Situations

Increase monitoring frequency to every 1-2 weeks after dose adjustments, addition of interacting medications (NSAIDs, ACE inhibitors, ARBs, thiazide diuretics), changes in renal function, significant weight changes, or acute illness. 1

Acute Treatment Phase

• Check lithium levels twice per week until both serum level and clinical condition stabilize during acute treatment 1, 7
• Steady-state concentrations are reached after 7-8 days (approximately 5-7 half-lives) 1

Impaired Renal Function

• If eGFR <60 mL/min/1.73 m²: increase monitoring frequency beyond standard 3-6 month intervals 1
• If eGFR <30 mL/min/1.73 m²: monitor at least monthly and consider risk-benefit of continuing lithium 1
• Patients with reduced renal function require more frequent monitoring of lithium levels, electrolytes, and renal function 1

Drug Interactions

• Patients taking NSAIDs, ACE inhibitors, ARBs, or thiazide diuretics require increased monitoring frequency due to elevated lithium toxicity risk 1
• Potassium >5.5 mmol/L requires review of lithium dose and consideration of temporary discontinuation 1

Intercurrent Illness

• Temporarily discontinue lithium during serious intercurrent illness that increases acute kidney injury risk (if eGFR <60 mL/min/1.73 m²), planned IV radiocontrast administration, bowel preparation, or prior to major surgery 1, 7
• Check lithium levels and renal function more frequently during and after illness 1, 7

Critical Monitoring Pitfalls to Avoid

• Never rely on lithium levels alone—toxicity can occur at therapeutic levels, particularly in chronic toxicity or with drug interactions 2
• Avoid concomitant NSAIDs whenever possible due to significant nephrotoxicity risk and increased lithium levels 1, 7
• Always start steroids before thyroid hormone replacement if both adrenal insufficiency and hypothyroidism are present, to avoid precipitating adrenal crisis 8
• Do not wait beyond 7-8 days to check initial lithium levels after starting therapy or dose adjustment, as steady state is achieved and delays risk toxicity 1
• Monitor for early toxicity signs including tremor, nausea, diarrhea, and polyuria-polydipsia, which warrant immediate level checking 7
• Women under 60 years are at highest risk for renal and thyroid dysfunction and may warrant more frequent monitoring 3