Serum Lithium

Specimen Required

3-5cc Clotted Blood or Serum

Fasting Required

Purpose of the Test

To determine the lithium concentration in the blood to maintain an appropriate level or to detect lithium toxicity

When this test is required

Lithium salts are potentially toxic and should not be prescribed unless facilities for monitoring serum lithium concentration are available (British National Formulary, 2022).Lithium tests are often requested when a patient is starting lithium treatment or returning to it after an absence. Once stable blood concentrations in the therapeutic range have been achieved, then lithium should be monitored at regular intervals (3 monthly in the first year, 3-6 monthly thereafter) to ensure that the concentration remains in this range. Different brands of lithium release lithium into the stomach differently, and blood testing may be required if the brand of lithium is changed, to ensure that blood levels stay the same.The test may also be requested when a patient’s condition does not appear to be responding to lithium to determine whether concentrations are too low, the medication is ineffective, or if the patient is taking the lithium as prescribed. It may also be requested when a patient experiences a troublesome level of side effects and/or exhibits symptoms that the doctor suspects may be due to toxicity.Patients should talk to their doctor about the timing of the sample collection. Lithium blood levels must be performed at least 12 hours (usually 12-18 hours) after the last dose of lithium. Since dosage timing varies and some types of tablet release lithium more slowly, detailed collection instructions may vary.

What the Test Detects

This test measures the amount of lithium in the blood. Lithium is a drug that is used to treat mood disorders such as bipolar disorder, a mental condition that is characterised by cycles of depression and mania. These cycles may be as short as a few days or weeks or may be months or years long. During a depressive episode, those affected may feel sad, hopeless, worthless, and lose interest in daily activities. They may be tired but have trouble sleeping, experience weight loss or gain, have difficulty concentrating, and have thoughts of suicide. During a manic episode, those affected may be euphoric, irritable, have high energy and grandiose ideas, use poor judgment, and participate in risky behaviour. Sometimes affected patients will have mixed episodes with aspects of both mania and depression. Bipolar disorder can affect both adults and children.Lithium is prescribed to even out the moods of the person with bipolar disorder and is sometimes prescribed for patients with recurrent depression who are not responding well to other medications. It may take several weeks to months for lithium to affect a person’s mood. Dosages of the drug are adjusted until a steady concentration in the blood is reached. The actual amount of drug that it will take to reach this steady state will vary from person to person and may be affected by the individual’s age, general state of health, and other medications. Lithium levels must be maintained within a narrow therapeutic range. Too little lithium and the medication will not be effective; too much and patients will experience symptoms of lithium toxicity, such as, nausea, vomiting, diarrhoea, stomach ache, confusion, blurred vision, sleepiness and tremors (shaking). Patients experiencing any of these symptoms should consult their doctor promptly. Extremely high lithium levels can lead to loss of consciousness and/or seizures, and can be fatal.

Preparation for the Test

No test preparation is needed. However, timing of the sample collection may affect results. Lithium blood levels must be performed at least 12 hours (usually 12-18 hours) after the last dose of lithium. Tell the person who draws your blood when you took your last dose so that the results can be interpreted correctly.

Sample Requirements

A blood sample is obtained by inserting a needle into a vein in the arm.

Additional Notes

Lithium is excreted mainly by the kidneys. Long-term use of lithium carries a risk of decreased kidney function. Patients with kidney disease may have increased lithium levels because of decreased elimination. Doctors will monitor kidney function over time with tests such as urea, and creatinine, before starting treatment and at intervals thereafter, usually every six months.Lithium levels and side effects can increase with the loss of salt and water from the body, such as may occur with a low-salt or salt=-ree diet, excessive sweating, or with an illness that causes dehydration, vomiting or diarrhoea. If sickness and diarrhoea persists for a day or two, or if food or fluid intake is reduced, patients should contact their doctor urgently. Patients who take lithium may develop hypothyroidism (decreased thyroid function). Doctors will regularly monitor a patient’s thyroid function with a TSH and/or a T4 test before starting treatment and at intervals thereafter usually every six months.Women who use lithium during pregnancy are at an increased risk of having their baby develop a rare heart valve defect. Women who want to become pregnant while taking lithium should talk to their doctors, but it is important not to stop taking lithium without medical advice.. There are two different types of lithium preparation – lithium carbonate and lithium citrate. Lithium citrate comes as a liquid and is usually only prescribed for patients who have difficulty swallowing tablets. It is important not to change to a different type of preparation unless recommended to do ao by a doctor.A variety of prescribed drugs, over-the-counter medications, and supplements can increase, decrease, or interfere with the concentrations of lithium in the blood. Drugs that can increase lithium concentrations include anti-inflammatory agents such as aspirin, ibuprofen and naproxen and diuretics such as bendroflumethazide and furosemide. Drugs that can increase the side effects of lithium include antidepressants such as paroxetine fluoxetine and antipsychotics such as clozapine and olanzapine, blood pressure medications such as calcium channel blockers and angiotensin converting enzyme inhibitors (enalapril, lisinopril, ramipril) and antiseizure medications such as carbamazepine and phenytoin.Drugs that can decrease lithium concentrations include theophylline and prescription levels of caffeine.All patients on lithium therapy are recommended to carry a ‘Lithium Alert Card’ to alert health professionals that they are taking lithium, and to keep a ‘Lithium Record Book’ recording details of their treatment. In the UK, the Lithium Treatment Pack (“Purple Book” can be obtained from your doctor or your pharmacist.

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