Tests & procedures
Lithium blood tests
Why regular blood tests matter while taking lithium, and how to prepare for them.
Why it matters
Lithium works within a narrow range — too little may not help, and too much can be harmful — so regular blood tests check the level in your body and that your kidneys and thyroid are healthy. The level is never read on its own: your team interprets it alongside how you are feeling, your kidney function, and the dose you have actually been taking.
How to prepare
Step by step
Before
Keep to your usual dose and your normal salt and fluid intake.
On the day
Blood taken about 12 hours after your last dose. Taking lithium at night does not turn the next morning's sample into a full 24-hour one — the 12-hour interval is what the result is read against.
After a dose change
It usually takes about 5 to 7 days for the level to settle after a change, which is a different thing from the 12-hour gap before a test. If you feel unwell in the meantime, do not wait for either interval to pass.
After the test
Your team reviews the level alongside kidney function, electrolytes, thyroid and calcium results. How often these are repeated depends on the plan you and your team are following.
- New or worsening vomiting or diarrhoea
- A coarse, shaky tremor
- Feeling unsteady on your feet
- Slurred speech
- Confusion, or feeling much more drowsy than usual
- Blurred vision, or muscle twitching or jerking
- Do not take the next dose until you have spoken to a clinician or the Poisons Information Centre
- Call 000 or go to an emergency department if you are confused, unsteady on your feet, slurring your speech or very drowsy
- Otherwise call the Poisons Information Centre on 13 11 26 now, even if you feel only mildly unwell — do not wait for your next blood test
Staying safe between tests
Keep your fluid and salt intake reasonably steady and avoid sudden changes. Being unwell with vomiting, diarrhoea, fever or dehydration can push your lithium level up — treat that as urgent: call your doctor, pharmacist, or the Poisons Information Centre on 13 11 26, and do not take the next dose until advised. Check with your doctor or pharmacist before starting or changing any medicine, including anti-inflammatories bought over the counter, and medicines for blood pressure or fluid — these can change your lithium level. Tell your doctor if you are pregnant or planning a pregnancy, and never switch to a different lithium product without advice. For a suspected overdose, call the Poisons Information Centre on 13 11 26 straight away even if you feel well, and call 000 for a collapse, a seizure or any immediate danger.
Where this information comes from
Demonstration content — not clinician-approved. Governance-approved patient information must replace it before any clinical use or sharing.
This sheet is general information, not personal medical advice. Always follow the instructions from your own doctor or pharmacist.