Lithium erythrocyte/plasma ratio as a predictor of response

The authors measured RBC/plasma lithium ratios in 33 patients with primary diagnoses of unipolar depression (N=20), bipolar depression (N=9), schizo-affective psychosis (N=2), and alcoholism (N=2). Subjects rated as having marked or moderate improvement at follow-up (average = 17.1 months) tended to have high ratios (greater than or equal to .41), whereas all 9 patients rated as minimally improved were in the low-ratio group. Although further research with larger samples, controls, and longer follow-up is necessary, the results suggest a predictive value for the RBC/lithium ratio.