Metals, toxins and medication
Lithium
The lithium level checks the dose in people who take lithium as a medicine; it is not a preventive test.
Everything about this testWhat it measures
The analysis measures how much lithium is in your blood. Lithium is a medicine used mainly for bipolar disorder, and sometimes as an add-on in depression. The body does not make lithium itself: normally there is no lithium in the blood. The kidneys remove lithium, so the level depends strongly on kidney function and on the fluid and salt balance.
- Whether the lithium dose is in the right range in someone who takes this medicine
- A level that is too high, which may point to impending lithium poisoning
- A level that is too low, at which the medicine does not work well enough
High
A level that is too high means there is more lithium in the blood than the prescriber intends. According to the Farmacotherapeutisch Kompas (Dutch drug formulary), the dose is set to a target level that differs per situation, with an upper limit of 1.5 mmol/l; the Dutch Society for Clinical Chemistry (NVKC) considers a value above 1.5 mmol, measured 12 hours after intake, a sign of an increased risk of lithium poisoning. Early signs of this are drowsiness, trembling, muscle weakness, slurred speech, nausea and unsteady walking. Dehydration, fever, vomiting, diarrhea, a low-salt diet and certain medicines such as water pills (diuretics) and anti-inflammatory drugs can make the level rise quickly.
Low
A low level usually means that the dose is too low, that a dose was missed, or that absorption or breakdown is different than expected. According to the Farmacotherapeutisch Kompas, the desired effect is not reached with a level that is too low. In someone who does not take lithium, no lithium can normally be detected in the blood; a low or unmeasurable value is then expected and does not mean a deficiency.
Preparation
- Have your blood taken about 12 hours after your last lithium dose.
- Take your morning dose after the sample is taken.
If your result is abnormal
The prescriber adjusts the dose based on the level and repeats the measurement. With a level that is too high and signs of poisoning, immediate assessment by a doctor is needed.
Reliability
Lithium has a narrow therapeutic range: the difference between an effective level and a level that is too high is small. That is why the measurement can only be interpreted if the time of the blood draw is right. The Farmacotherapeutisch Kompas prescribes always measuring the level 12 hours after the last dose; if blood is taken earlier or later, the result is not usable. The level is part of the treatment of someone who takes lithium and says nothing about someone who does not take the medicine.
Limitations
- The time of the blood draw is decisive: only a measurement 12 hours after the last dose can be compared with the target values used.
- Dehydration, fever, vomiting, diarrhea and a low-salt diet raise the level.
- Water pills (diuretics), anti-inflammatory drugs (NSAIDs) and some blood pressure medicines can raise the level.
- Reduced kidney function slows the removal of lithium and raises the level.
How common is this
Bipolar disorder affects about 1 in 100 people. Lithium is one of the medicines used long term for it. Only people who take this medicine have a lithium level.
Who is this useful for
This is not a preventive test. The measurement is intended for people who take lithium; the prescriber requests the level and assesses it, together with kidney function and thyroid function. According to the Farmacotherapeutisch Kompas, once the dose is set, the level is checked at least every 3 to 6 months, and additionally during illness, when the dose changes or when new medicines are started. For people who do not take lithium, the measurement has no meaning.
Downsides and risks
- A measurement at a time other than 12 hours after intake gives a result that cannot be interpreted and can lead to a wrong dose adjustment.
- A level measured outside the treatment relationship, without information on kidney function, dose and timing, gives the prescriber no usable information.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results