Pattern of lithium exposure predicts poisoning severity: evaluation of referrals to a regional poisons unit.

BACKGROUND Lithium toxicity may result in severe clinical features. There is on-going uncertainty about the significance of serum lithium concentrations in patients with lithium toxicity. AIM To examine potential relationships between stated quantity of lithium ingested, serum lithium concentrations, and poisoning severity among patients referred to a regional poisons centre. METHODS Prospective evaluation of enquiries to the Scottish Poisons Information Bureau about lithium toxicity between 2000-2005 inclusive. RESULTS There were 172 enquiries, relating to acute ingestion (n = 101), acute-on-therapeutic ingestion (n = 38), or chronic poisoning (n = 33). Poisoning severity was moderate or severe in 9.9%, 26.3% (p < 0.05 vs. acute) and 54.5% (p < 0.005 vs. acute) of each group, respectively. Median (IQR) serum lithium concentrations in each group were: 2.4 (1.7-3.3) mmol/l, 2.1 (1.4-3.8) mmol/l, and 2.3 (1.9-3.3) mmol/l, respectively. The median stated quantities ingested in acute and acute-on-therapeutic lithium exposure were 5000 mg (2000-11 050 mg) and 4000 mg (2400-8820 mg), respectively. DISCUSSION Patients with acute-on-therapeutic and chronic poisoning are at greatest risk of severe toxicity. These differences cannot be explained by either the quantity of lithium ingested or serum lithium concentration alone.