Serum lithium reference ranges are defined for a trough sample taken about 12 hours after the last dose, usually the morning after an evening dose. A level drawn a few hours after a dose will read falsely high and can prompt an unnecessary dose cut.
Check levels about five days after starting or changing the dose, then at regular intervals once stable, alongside renal and thyroid function. Recheck promptly when a patient becomes dehydrated, starts a diuretic, an ACE inhibitor or an NSAID.
- Time lithium samples for about 12 hours after the last dose.
- Recheck about five days after any dose change.
- Monitor renal and thyroid function alongside levels.
- Recheck early when a patient becomes dehydrated or starts a diuretic, ACE inhibitor or NSAID.
Why it matters
A mistimed sample is one of the commonest reasons for a wrong lithium dose change.
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