Lithium ratio in psychiatric patients: a caveat

We divided bipolar patient samples into two groups: Group I (off lithium 10 days to 2 weeks, n = 14) and group II (off lithium 3 weeks or longer, n = 13). Only group I was significantly different from controls. The mean for group II was significantly different from that for group I but not that for controls. Previous reports may have exaggerated the number of "high ratio" patients due to a treatment artifact. We recommend that patients be tested only after having been withdrawn from lithium treatment for 3 weeks or more. Otherwise spurious differences between patients and controls may result.