How is it used?
The lithium test is used 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 used to measure blood levels every few days when a person first begins taking lithium to help adjust the dose and reach the desired blood level. The test may be used at regular intervals or as needed to monitor blood concentrations. One or more lithium tests may be ordered if a person starts taking additional medications to judge their effect, if any, on lithium levels and may be ordered if the doctor suspects toxicity.
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When is it ordered?
Lithium is ordered frequently when a person 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 drug levels remain in this range.
The test may be ordered when a person'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 person is complying with therapy (taking the lithium regularly). It may also be ordered when someone experiences a troublesome level of side effects and/or exhibits symptoms that the doctor suspects may be due to toxicity. Some and of lithium toxicity include:
- Drowsiness, lack of energy
- Muscle weakness
- Lack of coordination
- Slurred speech
- Nausea, vomiting and/or diarrhea
- Confusion
- Irregular tremors or shaking
Blood samples for lithium levels are generally drawn 12-18 hours after the last dose. Since dosage timing varies and some formulations are time-released, collection specifics may vary.
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What does the test result mean?
The therapeutic range for lithium has been established at 0.6 - 1.2 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. People 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 and the doctor and affected person are satisfied that the person's bipolar disorder is being appropriately managed, then the dosage of lithium is adequate, particularly if the person is not experiencing significant side effects. If the blood level is below the therapeutic range, it is likely that the affected person is not receiving adequate medication. If levels are above the therapeutic range and if there are significant side effects present at the current dose, then it is likely that the dose is too high. However, people should not decrease or stop taking their medication without consulting with their doctor as it can worsen their bipolar symptoms. Dosage determinations and adjustments must be evaluated on a case-by-case basis.
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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. People with
kidney disease may have increased lithium levels because of decreased elimination. Doctors will monitor kidney function over time with tests such as a
BUN and
creatinine.
People who take lithium may develop hypothyroidism. Doctors will often regularly monitor a person's thyroid function with a TSH test.
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 such as hydrochlorothiazide and furosemide. 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 diarrhea.
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