Only relatively higher and lower Li⁺ ratio might predict clinical responses

Objective: To revisit the controversial issue regarding any possible relationship between Li⁺ ratio and clinical response with a view to explaining the contradictory reports on the subject. Method: Analysis of Li⁺ ratio and clinical response in 98 bipolar patients. The patients selected in this study were based on the following criteria: (i) fulfilment of DSM-III-R criteria for bipolar disorder; (ii) indication for long-term lithium therapy; (iii) continued lithium therapy for at least 2 years; (iv) had data on lithium ratio. Clinical responses were classified into good responders and poor responders (partial responder + nonresponder). Results: High lithium ratio (≥ 0.50) was associated with better clinical response (χ² = 5.80, d.f. = 1, P < 0.05). In a further analysis, subjects with lithium ratios in the range (mean + 1SD) or (0.50-0.67) and mean - 1SD or (0.32-0.49) showed the highest and lowest response rates. However, lithium ratios lower than 0.32 appear to be associated with a high response rate. Conclusion: The inconsistent results concerning the association between lithium ratio and clinical response reported since the 1970s may have been at least partially due or related to the inadequate inclusion of extreme lithium ratio data. However, this hypothesis needs to be tested in a larger, prospective study.