From the Guidelines
For patients on lithium, regular blood monitoring is crucial to prevent toxicity and ensure therapeutic efficacy, and this should include baseline and periodic assessments of complete blood count, renal function, electrolytes, thyroid function, and serum lithium levels, as recommended by recent guidelines 1. When initiating lithium therapy, baseline laboratory tests should include:
- Complete blood count
- Renal function tests (creatinine, BUN, eGFR)
- Electrolytes (especially sodium)
- Thyroid function tests
- Calcium levels
- Pregnancy test if applicable, as suggested by earlier studies 1 After starting lithium, serum lithium levels should be checked:
- Weekly until stable
- Every 3 months for the first year
- Every 6-12 months thereafter, with adjustments as needed based on clinical judgment and patient factors The therapeutic range for lithium is typically 0.6-1.2 mmol/L, with lower targets (0.4-0.8 mmol/L) for maintenance therapy, and blood samples for lithium levels should be drawn 12 hours after the last dose, typically in the morning before the first daily dose 1. More frequent monitoring is necessary for:
- Dose changes
- Medication interactions
- Illness
- Dehydration
- Signs of toxicity, which can include tremor, confusion, ataxia, and potentially seizures or coma if lithium levels exceed 1.5 mmol/L Long-term lithium use can affect kidney and thyroid function, hence the need for ongoing monitoring of these systems, as emphasized by the recommendation to regularly monitor GFR, electrolytes, and drug levels in patients taking potentially nephrotoxic agents like lithium 1.
From the FDA Drug Label
Blood samples for serum lithium determination should be drawn immediately prior to the next dose when lithium concentrations are relatively stable (i.e., 8-12 hours after the next dose).
- Serum lithium levels should be determined:
- Twice per week during the acute phase
- Until the serum level and clinical condition of the patient have been stabilized
- At least every two months during maintenance therapy
- Blood samples should be drawn 8-12 hours after the previous dose, immediately prior to the next dose 2
- Monitoring is necessary to avoid lithium toxicity, which can occur at doses close to therapeutic levels 2
From the Research
Blood Tests for Patients on Lithium
When monitoring patients on lithium, several blood tests are recommended to assess kidney function and prevent potential complications. These tests include:
- Serum creatinine concentration: This test measures the level of creatinine in the blood, which can be influenced by extrarenal factors 3.
- Estimated glomerular filtration rate (eGFR): This test estimates the rate at which the kidneys filter waste from the blood and can be used to monitor kidney function in patients on lithium 3, 4.
- Thyroid function tests: Lithium treatment can affect thyroid function, and regular monitoring is recommended to detect any abnormalities 5.
- Parathyroid function tests: Elevated ionized serum calcium and serum intact parathyroid hormone levels have been found in patients on lithium treatment 5.
Kidney Function Tests
Kidney function tests, such as serum creatinine, creatinine clearance, and eGFR, have limitations and can be influenced by various factors, including thyroid function 6. Cystatin C, a marker of kidney function, is strongly influenced by thyroid function and should be avoided in patients with thyroid disorders 6.
Monitoring Kidney Function
Regular monitoring of kidney function is essential for the safe and effective use of lithium 3, 4. This includes measuring urine osmolality, serum creatinine, and eGFR, as well as monitoring for signs of kidney damage or disease. By using these tests and monitoring kidney function regularly, healthcare providers can help prevent chronic kidney disease and other complications associated with lithium treatment 3, 4.