No, do not hold lithium for an AST of 50 U/L
An isolated AST of 50 U/L does not meet any threshold for discontinuing lithium therapy. This value represents only a mild elevation (typically <1.5× the upper limit of normal, assuming ULN ~40 U/L) and falls well below any established criteria for drug-induced liver injury that would warrant medication discontinuation 1.
Clinical Context and Decision Framework
Why This AST Level Does Not Require Action
The provided evidence focuses primarily on drug-induced liver injury (DILI) thresholds, which are instructive here:
For patients with normal baseline liver enzymes, drug discontinuation is typically considered only when ALT or AST reaches ≥8× ULN (approximately 320 U/L), or ≥3× ULN with concurrent total bilirubin ≥2× ULN or symptoms 2
An AST of 50 U/L represents approximately 1.25× ULN, which is classified as a mild elevation (mild is defined as <5× ULN) 3
At this level, the appropriate action is repeat testing and clinical observation, not medication discontinuation 2
Lithium-Specific Considerations
Lithium itself is not primarily hepatotoxic. The FDA labeling for lithium 1 lists contraindications as:
- Significant renal or cardiovascular disease
- Severe debilitation or dehydration
- Sodium depletion
- Concurrent diuretic use
Hepatic dysfunction is notably absent from lithium's contraindications or warnings. Lithium is almost exclusively excreted via the kidney, not metabolized by the liver 4.
Appropriate Management Algorithm
Step 1: Verify the Elevation
- Repeat AST along with ALT, alkaline phosphatase, and total bilirubin within 2-5 days 2
- Check if this represents a change from baseline or is a chronic finding
- Ensure the sample was properly collected (lithium heparin tubes can affect some enzyme measurements, though this is more relevant for CK and GGT) 5
Step 2: Assess Clinical Context
- Evaluate for symptoms: fatigue, nausea, vomiting, right upper quadrant pain, jaundice 2
- Review other medications that could contribute to hepatotoxicity
- Assess for alternative causes: alcohol use, viral hepatitis, fatty liver disease, other hepatotoxins 6, 7
Step 3: Continue Lithium with Monitoring
- Continue lithium at current dose 1
- Monitor lithium levels as per standard protocol (every 2 months during stable maintenance therapy) 1, 8
- Recheck liver enzymes in 2-4 weeks if initial repeat shows persistent mild elevation
- Maintain therapeutic lithium levels of 0.6-0.8 mEq/L for maintenance therapy 1, 4, 8
Critical Thresholds to Remember
Only consider holding lithium if liver enzymes reach:
- AST/ALT ≥8× ULN (~320 U/L) without other abnormalities
- AST/ALT ≥3× ULN (~120 U/L) plus total bilirubin ≥2× ULN or INR >1.5
- AST/ALT ≥3× ULN (~120 U/L) plus severe hepatic symptoms 2
Common Pitfalls to Avoid
- Do not discontinue lithium prematurely for mild, asymptomatic transaminase elevations—this can destabilize bipolar disorder and increase suicide risk
- Do not confuse AST elevation with hepatotoxicity—AST can be elevated from non-hepatic sources (cardiac, skeletal muscle, hemolysis) 3
- Do not apply DILI discontinuation rules designed for clinical trial settings to routine clinical practice without considering the specific drug's hepatotoxic potential
- Remember that lithium's primary toxicity concerns are renal and neurological, not hepatic 1
The risk-benefit analysis strongly favors continuing lithium therapy at an AST of 50 U/L, given lithium's proven efficacy in reducing morbidity and mortality (including suicide prevention) in bipolar disorder 8.