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Blood Test Tracker

Lithium

Measures how much lithium, a mood-stabilizing medicine, is in your blood so your care team can keep it in a range that works and is safe.

AI-verified against cited sources. Awaiting expert reviewAlso called LiLOINC 14334-7

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What it is

Lithium is a prescription medicine used mainly for bipolar disorder. Your kidneys clear it from your blood, and the gap between a helpful level and a harmful one is small. That is why this test is done regularly. The blood is usually drawn about 12 hours after your last dose and just before the next one, when the level is steadiest.

Why it matters

The FDA label warns that lithium toxicity is closely related to blood levels and can occur at doses close to the usual treatment range. Kidney function, dehydration, salt intake, illness and some common medicines can all push the level up. Checking it on a regular schedule lets your team catch a rising level before it causes harm. The label also says the number should not be relied on alone, so your symptoms matter too.

If it’s low

A level below 0.6 mmol/L is under the usual maintenance range, so lithium may be giving less protection than your team intended. It can also reflect when the blood was drawn. Your care team looks at the number together with how you are feeling.

Common causes

  • Missed or skipped doses
  • A sample drawn much later than 12 hours after the last dose
  • A dose change in the last few days, before the level has settled
  • Taking the medicine at different times than prescribed

What can help

  • Tell your care team about any missed doses
  • Ask whether the timing of your blood draw matched your dosing schedule
  • Check with your care team before changing or skipping any dose

If it’s high

A level above the usual range means more lithium is in your blood than expected. At higher levels, side effects such as hand tremor, nausea, diarrhea, thirst and frequent urination become more likely, and the FDA label calls levels of 1.5 mEq/L (the same as 1.5 mmol/L) and above toxic. Older adults and some other people can have symptoms at lower levels. Your care team will decide what to do.

Common causes

  • Dehydration from vomiting, diarrhea, fever or heavy sweating
  • Reduced kidney function, since lithium leaves the body through the kidneys
  • Low salt intake or sodium loss, because the kidneys handle lithium and sodium together
  • Medicines that raise lithium levels, including NSAID pain relievers, ACE inhibitors, ARBs and some water pills
  • Older age
  • A sample drawn soon after a dose instead of about 12 hours later
  • Taking more than prescribed

What can help

  • Keep your fluid and salt intake steady, as your care team advised
  • Call your care team if you have vomiting, diarrhea or a fever, since you can lose fluid quickly
  • Ask your care team before using over-the-counter pain relievers such as ibuprofen or naproxen
  • Tell every clinician you see that you take lithium

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 0.6–1.2 mmol/L. Source: ANI Pharmaceuticals, via DailyMed (NIH National Library of Medicine), National Institute for Health and Care Excellence (NICE). Labs treat above 1.6 mmol/L as urgent.

If this applies to you

Lithium means a little more for some people. Open the one that fits you.

Taking lithium

The lithium level shows whether the amount in the blood is in the range your clinician is aiming for. NICE suggests checking it 1 week after starting and after every dose change, weekly until stable, every 3 months in the first year, then every 6 months for most people.

Blood tests on lithium

What can affect your result

  • Time between your last dose and the blood draw
  • Kidney function
  • Hydration, salt intake, vomiting, diarrhea and sweating
  • Medicines such as NSAIDs, ACE inhibitors, ARBs and some water pills
  • Age
  • The blood tube used (lithium-heparin tubes give false high results)
  • Blood collected in a lithium-heparin (green-top) tube falsely raises the result. Serum from a plain red-top tube, or plasma from a tube without lithium, should be used.
  • A sample drawn soon after a dose will read higher than a true trough.

A trough: about 12 hours after your last dose and just before the next one (the FDA label says 8 to 12 hours). About a week to settle at a new level after a dose change. The label reports a half-life of about 24 hours, and NICE advises checking a level 1 week after starting lithium or changing the dose.

When to talk to a clinician

A level of 1.5 mmol/L or higher is in the range the FDA label calls toxic, and 1.6 mmol/L or higher is on ARUP's critical-values list. If you get a result at or above 1.5, contact your clinician today, even if you feel well. Call 911 or your local emergency number for confusion, severe tremor, trouble walking, slurred speech, a seizure, fainting, or vomiting that will not stop. NICE also advises seeking medical care if you develop diarrhea or vomiting, and talking with your doctor as soon as possible if you become pregnant or plan a pregnancy.

Questions you could ask

  • How often should my lithium level and kidney function be checked?
  • What should I do if I have vomiting, diarrhea or a fever?
  • What level am I aiming for, and why?
  • Could an illness or one of my other medicines have raised my level?
  • How are my kidney and thyroid tests?
  • Could a missed dose or the timing of the draw explain a low level?

Questions people ask

Why is my blood drawn 12 hours after my dose?

Lithium levels peak soon after a dose and then settle. About 12 hours after the dose, the level is steady and comparable from one test to the next. A sample taken sooner reads higher and can look like a problem that isn't there.

Is mmol/L the same as mEq/L?

For lithium, yes. One mmol/L equals one mEq/L, so a result of 0.8 in either unit means the same thing.

Why is my target different from what I read online?

Guidelines differ. The FDA label gives 0.6 to 1.2 for long-term use, while NICE in England aims for 0.6 to 0.8 for first-time users and 0.8 to 1.0 for people who relapsed. Your prescriber sets the target that fits you.

Show the science and sources

Units

  • 1 mmol/L = 1 mmol/L
  • 1 mmol/L = 1 mEq/L

For clinicians and researchers

Lithium is a monovalent cation (atomic weight 6.94; lithium carbonate 73.89) with a volume of distribution near total body water and no protein binding. It is excreted almost entirely in urine, renal excretion is proportional to plasma concentration, and the elimination half-life is about 24 hours (FDA label). Lithium reduces tubular sodium reabsorption, so sodium depletion or volume contraction raises levels. Samples should be drawn as a 12-hour post-dose trough; the label says 8 to 12 hours. The FDA label gives a desirable long-term range of 0.6 to 1.2 mEq/L, toxicity at 1.5 mEq/L and above, mild to moderate reactions from 1.5 to 2.5, and moderate to severe reactions from 2.0 and above. NICE CG185 aims for 0.6 to 0.8 mmol/L in first-time use and 0.8 to 1.0 mmol/L after relapse or with subthreshold symptoms. The 2017 AGNP consensus uses 1.2 mmol/L as its laboratory alert level, which a 2026 survey found most hospital critical limits (median 1.6) exceed. Serum levels correlate imperfectly with brain levels and symptoms, and chronic accumulation can cause toxicity at lower serum levels than acute ingestion. Lithium-heparin collection tubes falsely raise results.

LOINC 14334-7 (primary), 74806-1, 3719-2, 3723-4. Specimen: serum.

Sources

  1. LITHOBID (lithium carbonate) extended-release tablets: prescribing information, ANI Pharmaceuticals, via DailyMed (NIH National Library of Medicine) (2026)
  2. Bipolar disorder: assessment and management (CG185), recommendations, National Institute for Health and Care Excellence (NICE) (2014)
  3. ARUP Laboratories Critical Values List, ARUP Laboratories (2026)
  4. Drug Critical Limits for Urgent Physician Notification, Clinical Pharmacology & Therapeutics (2026)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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