Lithium is a mood-stabilising medication used primarily for bipolar disorder. Because lithium has a narrow therapeutic window, regular blood level monitoring is essential. Too little provides no clinical benefit; too much causes toxicity. Blood lithium testing measures the serum concentration to ensure levels remain within the therapeutic range.
Lithium toxicity can range from mild (tremor, thirst, polyuria, nausea, diarrhoea) to severe (confusion, ataxia, seizures, cardiac arrhythmias, and kidney failure). Kidney function and thyroid function are also monitored in people on lithium, as long-term therapy can impair both. The standard monitoring target is a 12-hour post-dose trough level.
FAQs
How often should lithium levels be checked?
When starting or adjusting the dose, levels should be checked 5-7 days after the change. In stable patients on long-term therapy, monitoring every 3-6 months is standard, along with kidney and thyroid function tests. More frequent monitoring is needed if clinical factors change (new medications, illness, dehydration).
What are the signs of lithium toxicity?
Early signs include tremor, thirst, increased urination, nausea, diarrhoea, and mild confusion. Moderate toxicity causes increasing tremor, unsteadiness, slurred speech, and confusion. Severe toxicity causes seizures, heart rhythm abnormalities, kidney failure, and potentially coma. If toxicity is suspected, seek urgent medical review.
Why do NSAIDs and diuretics affect lithium levels?
NSAIDs reduce renal prostaglandin synthesis, decreasing kidney blood flow and lithium clearance. Diuretics cause sodium loss, prompting the kidney to reabsorb more sodium and lithium to compensate. Both can raise lithium to toxic levels without any dose change.
When should lithium be collected for monitoring?
Lithium should be collected exactly 12 hours after the last dose (the trough level). This standard timing is essential for accurate interpretation against therapeutic ranges. Samples collected at other times cannot be meaningfully compared.
