Lithium blood test explained

Lithium is a chemical element used as a medicine (a mood stabiliser) in bipolar disorder, mania, hypomania and severe depression that has not responded to other treatment. Unlike most blood markers, which reflect the body's own processes, the amount of lithium in the blood depends almost entirely on the dose of the medicine being taken — so this test is a therapeutic drug monitoring tool, not a diagnostic biomarker for healthy people. Lithium has a narrow therapeutic window: the amount that works therapeutically is close to the amount that already causes signs of poisoning, which is why regular blood testing is a necessary part of treatment. According to the NHS, blood is taken 12 hours after the last dose of the medicine, so that the result is comparable. Besides the lithium level itself, kidney and thyroid function are also monitored during treatment, because long-term lithium use can affect them.

• When starting treatment with lithium medicines — according to the NHS, blood is tested every week during the first weeks, while the dose is being stabilised
• Regularly during treatment, once the level is stable — according to the NHS, usually every 3–6 months
• After a dose change, or after adding a new medicine that could affect the amount of lithium in the blood
• When lithium poisoning is suspected — nausea, vomiting, tremor, blurred vision or confusion
• Before surgery or during dehydration, when the lithium level can change suddenly

The exact therapeutic range (the normal range) is set by the doctor individually, taking into account the diagnosis and the form of the medicine — a single publicly published figure cannot be given without the doctor's context. The result always needs to be discussed with the doctor who prescribed the medicine, and assessed together with the range given on your own laboratory report.

Too high a lithium level

Too much lithium in the blood (lithium poisoning) is an urgent condition. According to the NHS, it can be caused by too high a dose, dehydration, a reduced amount of salt in the diet, some other medicines, or worsened kidney function, because lithium is removed through the kidneys.

Possible causes of a high level

• Too high a dose of lithium, or increasing it without enough monitoring
• Dehydration, or a reduced amount of fluid or salt (sodium) in the body
• Worsened kidney function — lithium is removed through the kidneys, so a kidney disorder slows its removal
• Some medicines taken at the same time — for example certain medicines that affect blood pressure or fluid balance (diuretics), or anti-inflammatory medicines (NSAIDs)

Signs of too much lithium

• Nausea, vomiting, diarrhoea, abdominal pain
• Blurred vision
• Passing urine more often, reduced control of urine or bowel movements
• Dizziness, drowsiness
• Confusion, clouding of consciousness
• Tremor, muscle weakness, twitching or spasms
• Speech problems

• Any signs of poisoning (nausea, tremor, confusion) call for urgent help — tell the doctor about them immediately
• Kidney function markers (creatinine) and electrolytes (sodium, potassium) — they help assess whether lithium is being removed properly
• Whether other medicines being taken or the diet (the amount of salt) have changed, as these can affect the lithium concentration
• Adjusting the dose — only on the doctor's decision, based on a repeat blood test

Too low a lithium level

Too little lithium in the blood means the dose of the medicine may not be enough for the therapeutic effect — stabilising mood. According to the NHS, regular blood tests are there precisely so that lithium is neither too high nor too low.

Possible causes of a low level

• Too low a prescribed dose of lithium
• Missed doses of the medicine, or taking it irregularly
• Increased removal of lithium from the body (for example because of an increased amount of fluid, or certain kidney conditions)

What is assessed alongside a low result

• Whether the medicine is being taken regularly, at the prescribed dose and time
• The return or worsening of mood symptoms — it is important to tell the doctor about this
• A review of the dose and a repeat blood test after the adjustment, only on the doctor's decision

Related tests

• Sodium and potassium — electrolytes assessed alongside lithium
• Creatinine — kidney function, since lithium is removed through the kidneys
• TSH — thyroid function, monitored during lithium treatment
• Calcium — another related blood test