What this test measures
Lithium is one of the oldest and most effective mood stabilisers, used in bipolar disorder, recurrent unipolar depression as augmentation, and to reduce suicide risk. Unlike most psychiatric drugs, lithium has a narrow therapeutic window: the difference between an effective level and a toxic level is small, so the dose must be guided by blood levels.
The assay measures the concentration of lithium ion in serum and is reported in mmol/L (or mEq/L — the same number). The standard sample is a 12-hour trough — drawn the morning after the previous evening dose, before the next dose is taken. Peak levels (1–3 hours post-dose) are higher and not used for routine monitoring.
Why it matters
Lithium remains the gold standard for long-term bipolar prophylaxis. Indian psychiatrists prescribe it widely because it is inexpensive and proven — but it needs regular monitoring. Levels are affected by hydration, salt intake, kidney function, sweating, NSAIDs, ACE inhibitors, and diuretics. A patient stable for years can become toxic during a summer heat wave, a bout of gastroenteritis, or after starting a new blood-pressure pill.
Clinical monitoring schedule: check level 5–7 days after starting or changing dose, then every 3 months once stable; every 6 months in long-standing stable patients. Also check kidney function (creatinine, eGFR) and thyroid (TSH) at the same visit, because chronic lithium can affect both organs.
How to prepare
Sample timing is critical — draw exactly 12 hours after the previous evening dose, before the morning dose. If your last dose was at 9 pm, the sample should be at 9 am. Bring a note of your dosing schedule so the lab can verify the trough. No fasting is needed. Continue all other medications. Stay well hydrated in the 24 hours before the test — dehydration falsely elevates lithium.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Lithium (mmol/L (mEq/L))[1][2][3] | Therapeutic 0.6 – 1.2 mmol/L (acute mania up to 1.2 · maintenance 0.6 – 0.8) | < 0.4 mmol/L: sub-therapeutic — risk of relapse. May indicate non-adherence, increased renal clearance (pregnancy, young age), or sample drawn too late after the dose. | 1.2 – 1.5 mmol/L: borderline; watch for tremor, GI upset. 1.5 – 2.0 mmol/L: mild toxicity — coarse tremor, drowsiness, vomiting, ataxia. 2.0 – 2.5 mmol/L: moderate toxicity — confusion, hyperreflexia, myoclonus. > 2.5 mmol/L: severe toxicity — seizures, coma, renal failure, cardiac arrhythmia; requires haemodialysis. |
Lithium serum levels — therapeutic and toxic ranges
| Lithium (mmol/L) | Category | Clinical implication |
|---|---|---|
| < 0.4 | Sub-therapeutic | Likely under-dosed or non-adherent; mood relapse risk |
| 0.6 – 0.8 | Maintenance therapeutic | Target for long-term prophylaxis in bipolar disorder |
| 0.8 – 1.2 | Acute therapeutic | Target for acute mania; monitor closely |
| 1.2 – 1.5 | Borderline / high | Early side effects: tremor, GI upset; reduce dose |
| 1.5 – 2.5 | Toxic | Ataxia, confusion, hyperreflexia — hospital admission |
| > 2.5 | Severe toxicity | Seizures, coma — haemodialysis indicated |
Frequently asked questions
Why must lithium be drawn exactly 12 hours after the dose?
Lithium levels follow a predictable curve after each dose — they peak 1–3 hours after, then fall steadily. A "trough" level drawn 12 hours after the last dose is comparable from visit to visit and from patient to patient. Sampling at a random time gives a number that cannot be safely interpreted.
What is a safe lithium level?
For long-term maintenance, 0.6–0.8 mmol/L is the modern target. For acute mania, doctors may push up to 1.0–1.2 mmol/L for a few weeks. Above 1.2 mmol/L the side-effect rate climbs steeply, and above 1.5 mmol/L lithium is considered toxic.
How often should I get a lithium level checked?
After starting or changing dose: 5–7 days later. Once stable: every 3 months. Long-term stable patients: every 6 months. Also check whenever you start a new medication that can affect lithium (NSAIDs, ACE inhibitors, diuretics) or after illness with vomiting, diarrhoea, or fever.
Can dehydration cause lithium toxicity?
Yes — and it is one of the most common causes of toxicity in India. Hot weather, gastroenteritis, vomiting, sweating during fever, or restricted fluid intake all concentrate lithium in the blood. Drink water consistently and avoid sudden low-salt diets while on lithium.
Which other tests are done alongside lithium?
Kidney function (creatinine, eGFR) at every level check; thyroid (TSH) every 6 months; calcium yearly. Long-term lithium can affect kidney concentrating ability and the thyroid (causing hypothyroidism), so these are baseline and follow-up tests.
What are the early signs of lithium toxicity?
New or worsening coarse tremor, drowsiness, slurred speech, nausea, diarrhoea, unsteadiness, blurred vision, muscle twitching. If any of these appear, hold the next dose and get a level the same day. Severe toxicity can progress to seizures and coma.
Should I take my morning dose before the blood test?
No. The trough sample is drawn before the morning dose. Take your medication immediately after the blood is drawn so you do not miss the dose.
Can I stop lithium suddenly?
No — abrupt withdrawal is associated with a high risk of mood relapse, sometimes within weeks. Any reduction or stop should be planned with your psychiatrist over weeks to months.
Related Drugs / Therapeutic Monitoring tests
Tests commonly ordered alongside LITHIUM, or that help interpret an unexpected result.
Sources & references
- NCBI StatPearls — Lithium Toxicity · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Lithium Test · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Lithium, Serum · accessed 2026-05-30T00:00:00.000Z
- FDA — Lithium Carbonate Prescribing Information · accessed 2026-05-30T00:00:00.000Z
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