The target serum lithium concentration ranges between 0.4 and 0.8 mmol/1. Concentrations above 1 mmol/1 are associated with an increased risk of toxicity. Take blood samples at a standard time—12 h after the last dose. In my view routine monitoring is unnecessary, and the serum lithium concentration should be measured at times when toxicity is most likely, for example in patients with changing renal function or with acute alterations in electrolyte balance. However, this is a contentious view, and most psychiatrists prefer to measure the serum lithium concentration routinely at, say, 3- or 6-monthly intervals. Regular monitoring certainly emphasizes the dangers to the patient and gives an opportunity for a consultation, but it is no substitute for proper monitoring at the appropriate times.
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