Unit Converter
Lithium (Li)
(Therapeutic Drug Monitoring – Key Marker for Bipolar Disorder Management & Toxicity)
Synonyms
- Lithium
- Serum lithium
- Lithium level
- Li⁺ ion concentration
Units of Measurement
- µmol/L
- mmol/L
- mg/dL
- mg/100 mL
- mg%
- mg/L
- µg/mL
- mEq/L
Molecular Weight
Lithium ion = 6.94 g/mol
Key Unit Conversions
1. Mass ↔ Molar
1 mmol/L = 6.94 mg/L
1 µmol/L = 0.00694 mg/L
1 mg/L = 0.144 mmol/L
1 mg/dL = 10 mg/L = 1.44 mmol/L
2. mEq/L
Lithium is monovalent →
1 mmol = 1 mEq
1 mEq/L = 1 mmol/L
3. µg/mL
1 µg/mL = 1 mg/L
4. mg%
mg% = mg/dL
Description
Lithium is a monovalent cation (Li⁺) used as a mood stabilizer in psychiatry.
Major uses:
- Bipolar disorder (mania & maintenance)
- Schizoaffective disorder
- Aggression reduction
- Adjunct in depression (augmentation therapy)
Lithium has a narrow therapeutic window, requiring routine monitoring to prevent:
- Neurotoxicity
- Renal toxicity
- Thyroid dysfunction
Mechanism of Action
- Inhibits inositol monophosphatase → affects second messengers
- Modulates GSK-3β, serotonin, norepinephrine pathways
- Stabilizes neuronal firing
- Reduces suicide risk significantly
Clinical Significance
HIGH Lithium (Toxicity)
(Major clinical concern)
1. Mild Toxicity
- >1.5 mEq/L (mmol/L)
Symptoms: - Tremor
- Weakness
- Nausea
- Polyuria / polydipsia
2. Moderate Toxicity
- 1.5 – 2.5 mEq/L
Symptoms: - Ataxia
- Confusion
- Slurred speech
- Agitation
- GI upset
3. Severe Toxicity
- >2.5 mEq/L
Symptoms: - Seizures
- Coma
- Arrhythmias
- Renal failure
- Neurotoxicity
Causes of Elevated Lithium
- Dehydration
- Renal impairment
- Drug interactions (NSAIDs, ACEI, thiazides)
- Acute overdose
- Sodium depletion
LOW Lithium
- Subtherapeutic dose
- Non-adherence
- Rapid renal clearance
- Drug interactions (caffeine, theophylline)
Clinical consequence: poor mood stabilization.
Therapeutic Range
(APA psychiatric guidelines + Mayo + ARUP)
Acute Mania
- 0.8 – 1.2 mEq/L (mmol/L)
Maintenance Therapy
- 0.6 – 1.0 mEq/L
Elderly
- 0.4 – 0.8 mEq/L (increased sensitivity)
Toxic Levels
- >1.5 mEq/L early toxicity
- >2.5 mEq/L severe/life-threatening
Reference Intervals (non-treated individuals)
- <0.2 mEq/L (essentially undetectable)
Diagnostic Uses
1. Therapeutic Drug Monitoring
Check levels:
- 12 hours after last dose (“trough level”)
- Weekly during initiation
- Every 3 months during maintenance
- More frequently in elderly or renal impairment
2. Suspected Lithium Toxicity
Measure urgently in:
- Confusion
- Ataxia
- GI symptoms
- Dehydration
3. Renal Function Assessment
Lithium clearance depends on kidney function
→ Must monitor creatinine & eGFR.
4. Thyroid Monitoring
Lithium can cause:
- Hypothyroidism
- Goiter
→ TSH testing recommended.
5. Pregnancy
Levels fluctuate; dose adjustments needed.
Analytical Notes
- Serum lithium (not plasma) preferred
- Collect at 12-hour post-dose
- Hemolysis has minimal effect
- Interferences: sodium changes, dehydration
- Lithium heparin tubes should NOT be used (falsely high)
Clinical Pearls
- Lithium toxicity mimics stroke - ataxia, slurred speech, confusion.
- Dehydration is the most common cause of sudden toxicity.
- NSAIDs, ACE inhibitors & thiazide diuretics increase lithium levels.
- Caffeine & theophylline lower lithium levels.
- Hemodialysis is required for severe toxicity (>3.5–4 mEq/L).
- Lithium reduces suicide risk by >60% — unique among mood stabilizers.
Interesting Fact
Lithium is the lightest metal in the periodic table, and uniquely, it is a natural element with powerful mood-stabilizing properties discovered serendipitously in the 1940s.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Therapeutic Drug Monitoring
- APA Guidelines - Bipolar Disorder Management
- Mayo Clinic Laboratories - Lithium Level
- ARUP Consult - Psychiatric Drug Monitoring
- AACT Toxicology Guidelines - Lithium Overdose
- MedlinePlus / NIH - Lithium Test