Lithium | Pathology Tests Explained

What is being tested?

This test measures the amount of lithium in the blood. Lithium is a drug that is used to treat bipolar disorder. Bipolar disorder is 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 fatigued 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 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 a person's age, general state of health, and other medications that they are taking. Lithium levels must be maintained within a narrow therapeutic range. Too little and the medication will not be effective; too much and patients will experience symptoms associated with lithium toxicity, such as nausea, vomiting, diarrhea, confusion, and tremors. Extremely high levels can lead to stupor, seizures, and can be fatal.

How is it used?

The lithium test is ordered to measure and monitor the amount of lithium in the blood in order to determine whether drug concentrations are in the therapeutic range. It may be ordered every few days when a patient first begins taking lithium to help adjust the dose to the desired blood level. The test may be ordered at regular intervals or as needed to monitor blood concentrations. One or more lithium tests may be ordered if a patient starts taking additional medications (to judge their effect, if any, on lithium levels) and may be ordered if the doctor suspects toxicity.

When is it requested?

Lithium is ordered frequently 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 may be monitored at regular intervals to ensure that it remains in this range.

The test may be ordered when a patient's condition does not appear to be responding to lithium to determine whether concentrations are too low, the medication is ineffective, and/or to determine if the patient is complying with therapy (taking the lithium regularly). It may also be ordered 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 are generally performed 12-18 hours after the last dose. Since dosage timing varies and some formulations are time released, collection specifics may vary.

What does the result mean?

The therapeutic range for lithium has previously been established at 0.6 - 1.2 mmol/L but recent studies have suggested a range of 0.6 - 1.0 mmol/L. Within this range, most people will respond to the drug without symptoms of toxicity. Response and side effects will be individual, however. Some people's bipolar condition will not be adequately treated at the low end of the therapeutic range and some people will experience excessive side effects at the upper end. Patients should work closely with their doctor to find the dosage and concentration that works the best for them.

In general, when lithium results are in the therapeutic range, the doctor and patient are satisfied that the patient's bipolar disorder is being appropriately managed and the patient is not experiencing significant side effects, then the dosage of lithium a patient is receiving is adequate. If the patient is below the therapeutic range, it is likely that they are not receiving adequate medication. If they are above the therapeutic range and/or are experiencing significant side effects at their current dose, then it is likely that they are taking too much medication. Patients should not decrease or stop taking their medication without consulting with their doctor, however, as it can worsen their bipolar symptoms. Dosage determinations and adjustments must be evaluated on a case-by-case basis.

Is there anything else I should know?

Lithium is excreted primarily 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 a urea and creatinine.

Patients who take lithium may develop hypothyroidism. Doctors will often regularly monitor a patient's thyroid function with a TSH and/or a free T4 test.

Women who use lithium during pregnancy are at an increased risk of having their foetus develop a rare heart valve defect. Women who want to become pregnant should talk to their doctors about this subject.

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 in the body include anti-inflammatories such as ibuprofen and naproxen and diuretics such as hydrochlorothiazide and frusemide. Drugs that can increase the side effects of lithium include antipsychotics such as clozapine and olanzapine, blood pressure medications such as calcium channel blockers and angiotensin converting enzyme inhibitors, and antiseizure medications such as carbamazepine. Drugs that can decrease lithium include theophylline and prescription levels of caffeine.

Lithium levels and side effects can increase with the loss of salt and water from the body, such as may occur with a salt-free diet, excessive sweating, or with an illness that causes vomiting and diarrhoea.

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