Lithium Level
Also written as: Serum lithium, Li level
The amount of lithium in blood, checked regularly because its safe window is narrow.
What it measures
The concentration of lithium, a mood-stabilizing medication, in the blood. The standard sample is a trough, drawn about 12 hours after the last dose, because that is the timing the published interpretation of levels is built on.
Why a doctor orders it
Routine monitoring is part of taking lithium: at the start, after any dose change, after other medications change, and periodically thereafter. The gap between an effective level and a harmful one is small, and the kidneys' handling of lithium shifts with hydration, salt intake, and other drugs, so the level moves even when the dose does not.
What is generally associated with a higher result
Higher levels are broadly associated with dehydration, reduced kidney function, reduced salt intake, and interacting medications - NSAIDs such as ibuprofen, thiazide diuretics, and ACE inhibitor blood pressure drugs are the classic examples. A sample drawn earlier than the standard 12 hours after a dose also reads higher without the true steady level having changed. The target range is individual and set by the prescriber.
What is generally associated with a lower result
Lower levels are broadly associated with missed doses, increased fluid and salt intake, pregnancy, which increases clearance, and drugs that speed elimination. Caffeine can nudge levels down as well.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- Timing - the standard draw is about 12 hours after the last dose, and earlier draws read high
- Hydration, heavy sweating, and hot weather
- Salt intake - large changes in either direction shift the level
- Over-the-counter NSAIDs such as ibuprofen and naproxen
- Caffeine intake
Questions to take to your appointment
- Was this drawn about 12 hours after my last dose?
- Which of my other medications, including over-the-counter ones, can move this level?
- What should I do about monitoring when I am ill, sweating heavily, or drinking less than usual?
- Are my kidney and thyroid tests being checked alongside this?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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