Lithium

The test measures blood lithium concentration in people treated with lithium. Lithium has a narrow therapeutic range: effective and potentially harmful levels are close together, so treatment is regularly monitored with blood tests.

Who the test is for

• people starting lithium, about a week after starting treatment and after every dose change until levels stabilise;
• people on long-term lithium treatment, at regular monitoring visits;
• people starting a medicine alongside lithium that can raise its level, such as an anti-inflammatory painkiller (ibuprofen, diclofenac), certain blood pressure medicines (ACE inhibitors, sartans) or diuretics;
• people taking lithium who have diarrhoea, vomiting, high fever or other substantial fluid loss;
• people taking lithium who develop symptoms suggesting an excessive level or whose mood changes.

What lithium is and why it is measured

Lithium salts, most often lithium carbonate, are medicines for bipolar disorder, previously called manic-depressive psychosis. They are used to treat manic episodes and, more often, for long-term prevention of new manic and depressive episodes. Psychiatrists sometimes also prescribe lithium alongside an antidepressant for depression responding inadequately to treatment. Exactly how lithium stabilises mood is still not fully understood.

The same dose does not produce the same blood level in everyone. Lithium is excreted by the kidneys, so levels depend on kidney function, fluid and salt intake and other medicines. Dosage is therefore determined by the measured concentration, not just the number of tablets.

During long-term treatment lithium is monitored regularly: according to UK NICE guidelines, every 3 months in the first year, then every 6 months, or every 3 months in older people, with medicines affecting lithium or if the last level was at the higher limit.

Preparation and sample

Lithium is measured in venous blood. Collection timing is crucial: blood is taken approximately 12 hours after the last dose. If you take it in the evening, blood is collected the next morning; take any morning dose only after collection. A sample taken earlier will show a higher value that cannot be compared with the recommended range, and two measurements can be compared only if blood was taken at the same interval after the dose.

Write down when you took the last dose and state this during collection. Do not skip medicine or change the dose before testing unless your doctor has told you to. Fasting is not needed unless other tests requiring it are performed the same day.

How to interpret the result

Lithium is expressed in mmol/L. A psychiatrist sets an individual target for each patient. NICE guidelines recommend 0,6 to 0,8 mmol/L for most people, and 0,8 to 1,0 mmol/L for some, for example after a previous relapse while taking lithium. Lower targets are often used in older people. The range printed on the report is a guide; the treating doctor decides on dosage.

• Below-target level may mean the dose is too low, the medicine is not taken regularly or blood was collected too long after the dose.
• Above-target level requires checking the dose and cause, for example dehydration, reduced kidney function or a new medicine.
• At levels above 1,5 mmol/L toxic effects are expected, but signs of poisoning can occur at lower values too, particularly in older people.

Signs of excessive lithium: urgent

Contact a doctor or emergency department immediately if diarrhoea or vomiting, marked hand tremor, unsteady walking, slurred speech, muscle twitching, confusion or unusual sleepiness develop while taking lithium. These may be signs of lithium poisoning, which needs urgent care rather than waiting for routine monitoring.

What else is monitored with lithium

Long-term lithium can affect the kidneys, thyroid and parathyroid glands. Before treatment and then approximately every 6 months, monitoring therefore includes creatinine with estimated glomerular filtration rate (eGFR), urea and electrolytes, calcium and TSH, alongside body weight. People with heart disease or risk factors also have an ECG before treatment. The treating doctor decides which tests you need and how often.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). During collection, state that this is a lithium level and when you took the last dose. Prices for all tests and panels are in the service price list.

Frequently asked questions

Should I skip a lithium dose before blood collection?

Do not skip the evening dose. Blood is collected about 12 hours afterwards; take the morning dose after collection. If you take it differently, for example once daily in the morning, agree collection timing with your doctor.

Can the lithium level change without changing the dose?

Yes. Levels rise with dehydration from heat, diarrhoea, vomiting or high fever, sudden changes in salt intake and some medicines, such as anti-inflammatory painkillers, certain blood pressure medicines and diuretics. Before taking a new medicine, including an over-the-counter one, tell the pharmacist or doctor that you take lithium.

Why is thyroid function monitored with lithium?

Lithium can slow thyroid function and sometimes enlarge the gland. If this happens the disorder is treated, while the psychiatrist decides whether lithium should continue. TSH is therefore checked before and during treatment.