What labs need to be checked prior to starting a patient with partial kidney disease on lithium (lithium carbonate)?

Pre-Lithium Laboratory Assessment in Patients with Partial Kidney Disease

Before starting lithium in a patient with pre-existing kidney disease, you must obtain baseline serum creatinine with calculated eGFR, electrolytes (sodium, potassium, calcium), complete blood count, thyroid function tests (TSH), and urinalysis with urine albumin-to-creatinine ratio (UACR). 1, 2, 3

Essential Baseline Laboratory Tests

Renal Function Assessment

• Serum creatinine with eGFR calculation using the CKD-EPI equation is mandatory before lithium initiation 4, 1, 3
• Urine albumin-to-creatinine ratio (UACR) in a spot urine sample to detect baseline proteinuria, which is more sensitive than dipstick urinalysis 4, 3
• Blood urea nitrogen (BUN) to differentiate pre-renal from intrinsic renal causes if creatinine is already elevated 2, 3
• Complete urinalysis with urine specific gravity to establish baseline concentrating ability, as lithium commonly causes nephrogenic diabetes insipidus 3, 5

The eGFR is critical because patients with eGFR <60 mL/min/1.73 m² require intensified monitoring and may need dose adjustments or alternative treatments 1, 2. In your patient with "partial kidney disease," if the eGFR is 30-60 mL/min/1.73 m² (CKD stage 3), nephrology consultation should be strongly considered before initiating lithium 1.

Electrolyte Panel

• Serum sodium, potassium, calcium, and magnesium must be checked, as electrolyte disturbances are common with lithium and can worsen with underlying kidney disease 1, 2, 3
• Baseline potassium is particularly important because potassium >5.5 mmol/L requires review before starting lithium 2
• Calcium screening is essential as 7% of lithium-treated patients develop hypercalcemia, though this is often neglected in monitoring 6

Additional Required Tests

• Thyroid function tests (TSH) are mandatory at baseline, as lithium commonly affects thyroid function 2, 7
• Complete blood count (CBC) with differential to document any pre-existing cytopenias that could be exacerbated by lithium 2

Critical Decision Points Based on Baseline eGFR

eGFR ≥60 mL/min/1.73 m²

• Lithium can be initiated with standard monitoring every 6 months 1, 2
• Consider more frequent monitoring (every 3 months) if other risk factors present 1

eGFR 45-60 mL/min/1.73 m² (CKD Stage 3a)

• Increase monitoring frequency to every 3 months 1
• Nephrology consultation should be considered 1
• Carefully evaluate risk-benefit ratio of lithium versus alternatives 1

eGFR 30-45 mL/min/1.73 m² (CKD Stage 3b)

• Strongly consider discontinuation or dose reduction with mandatory nephrology consultation 1
• If lithium is still chosen, monitoring must occur at least monthly 2
• Dosing intervals should be extended (not doses increased) to avoid toxicity 2

eGFR <30 mL/min/1.73 m² (CKD Stage 4-5)

• Lithium should generally be avoided 1
• If absolutely necessary, monitor at least monthly with nephrology co-management 2
• Risk of end-stage renal disease is substantially elevated 8, 9

Common Pitfalls and How to Avoid Them

Do not rely on serum creatinine alone—always calculate eGFR using CKD-EPI equation, as creatinine can be misleadingly normal in patients with reduced muscle mass 4, 3. However, note that eGFR is unreliable when creatinine is changing rapidly, so use absolute creatinine values in acute settings 3.

Do not use urine dipstick for albumin screening—UACR is more sensitive and should be the standard test 4. This is particularly important in patients with pre-existing kidney disease where early detection of worsening proteinuria is crucial.

Screen for concomitant nephrotoxic medications at baseline, particularly NSAIDs, ACE inhibitors, ARBs, and diuretics, as these significantly increase lithium nephrotoxicity risk 1, 2, 3. NSAIDs should be avoided entirely in lithium-treated patients 1.

Document baseline urine concentrating ability because 51% of lithium-treated patients develop impaired renal concentrating ability, and clinical symptoms do not reliably predict this complication 5. Baseline testing allows you to detect changes during treatment.

Post-Initiation Monitoring Schedule

Once lithium is started, serum lithium levels should be checked twice per week until stabilized during the acute phase 2, 7. After stabilization, the standard monitoring includes:

• Serum lithium levels, creatinine/eGFR, and electrolytes every 6 months in patients with normal baseline kidney function 1, 2
• Every 3 months if eGFR 45-60 mL/min/1.73 m² 1
• Monthly if eGFR <30 mL/min/1.73 m² 2
• Thyroid function and weight annually 2

Monitoring frequency must increase with dose changes, addition of interacting medications, acute illness, or significant weight changes 2.