RBC and plasma choline levels in control and depressed individuals: a critical evaluation.

Red blood cell (RBC) and plasma choline (Ch) were measured in 78 depressed, drug-free patients and in 23 normal, drug-free control subjects. RBC Ch levels displayed a huge variability among the patients, in contrast to those measured in normal controls. Plasma Ch levels, on the other hand, were more consistent within each group, and were correlated with age among the two populations studied. RBC Ch levels would appear to be independent of plasma Ch levels, and to be highly individualized and reproducible within each subject. A segment of the depressed population exhibited significantly higher RBC Ch levels than those seen in the normal control population. A clinical correlation of RBC and plasma Ch levels within the depressed population indicated that the patients with RBC Ch levels exceeding 35 nmole/ml might represent a diagnostically distinct subpopulation with specific clinical characteristics. Results presented here, although preliminary, suggest a role for RBC Ch as a biological marker in certain categories of depressive illness.