Alert: Inaccurate Lithium Assay Results

Abstract

Objectives: A patient who had experienced bipolar disorder for over 20 years and who had been euthymic for most of that period while highly compliant with lithium, had falsely low lithium levels reported over two periods, 6 years apart, and was actually lithium toxic on the most recent occasion. At that latter time the spuriously low lithium levels reported on the assay risked dispelling any clinical suspicion of lithium toxicity, although toxicity was later confirmed. Method: Case report. Results: The latter incident identified a serious problem, whereby it is likely that the particular assay risks generating spuriously low values when high serum levels of lithium are present – a so-called ‘hook phenomenon’ that has been described for some quantitative immunoassays. Conclusions: It is in situations of high potential gravity – when lithium toxicity is present – that lithium quantification is most likely to be compromised and low values generated. Also of grave concern is the fact that there are no regulatory processes in place to communicate this problem to lithium prescribers.