CBC for Lithium Initiation in Older Adults with Impaired Renal Function
A complete blood count (CBC) is recommended as part of baseline laboratory assessment before initiating lithium therapy, but it is not the primary concern in older adults with impaired renal function—renal function assessment and monitoring are far more critical for this population. 1, 2
Baseline Laboratory Testing Before Lithium Initiation
The standard pre-lithium workup should include:
- Complete blood count (CBC) 1, 2
- Thyroid function tests (TSH, free T4) 2
- Renal function (blood urea nitrogen, creatinine, GFR) 2
- Serum electrolytes including calcium 2
- Urinalysis 2
While CBC is part of the comprehensive baseline assessment, it serves primarily to establish a reference point rather than to identify contraindications to lithium therapy. 1
Critical Considerations for Impaired Renal Function
The FDA label explicitly warns that lithium should generally not be given to patients with significant renal disease, as the risk of lithium toxicity is very high in such patients. 3 If the psychiatric indication is life-threatening and other measures have failed, lithium may be undertaken with extreme caution, including daily serum lithium determinations, usually low doses, and hospitalization. 3
Renal Function Takes Priority
- Renal function must be assessed before starting lithium and monitored regularly to minimize toxicity risk in patients with impaired renal function. 4
- For patients with GFR < 60 mL/min/1.73 m², consider lower doses and more frequent monitoring. 2
- For patients with GFR < 30 mL/min/1.73 m², reduce dose by 50%. 2
Evidence of Renal Risk
Research demonstrates that patients with compromised renal function prior to lithium initiation have a 6.7-fold increased risk of progressing to severe renal impairment (CKD 4-5) compared to those with normal baseline function. 5 Almost half of patients with elevated baseline creatinine progressed to severe kidney disease during lithium treatment, versus only 10% of those with normal baseline function. 5
Special Considerations for Older Adults
For elderly patients, use lower starting doses (150 mg/day) due to increased sensitivity to lithium and reduced clearance. 2 Older patients who progress to severe renal impairment are characterized by higher burden of comorbid somatic diseases, particularly cardiovascular disease. 5
Monitoring Strategy After Initiation
Once lithium is started (if deemed appropriate despite renal impairment):
- Serum lithium concentrations should be checked twice per week during the acute phase until levels and clinical condition stabilize. 4, 1, 2
- More frequent monitoring is essential if symptoms of toxicity appear, regardless of scheduled intervals. 4
- Temporarily suspend lithium during intercurrent illness, planned IV radiocontrast administration, bowel preparation, or prior to major surgery to prevent toxicity. 4
Common Pitfalls to Avoid
- Failing to establish baseline renal function before initiating lithium is a critical error. 4
- Overlooking the need for dose reduction in patients with reduced GFR. 2
- Concurrent use of NSAIDs and diuretics can precipitate toxicity and necessitate earlier, more frequent monitoring. 4, 2
- Inadequate hydration, especially during intercurrent illness, increases toxicity risk. 2
Bottom Line
While CBC is part of standard baseline testing before lithium initiation 1, 2, the presence of impaired renal function in an older adult represents a relative contraindication to lithium therapy 3 and demands extraordinary caution, aggressive monitoring, and consideration of alternative mood stabilizers. The renal assessment—not the CBC—is the laboratory test that should guide the decision of whether to proceed with lithium in this high-risk population.