Platelet serotonin levels support depression scores for women with postpartum depression

OBJECTIVE: It is very challenging to make an unbiased diagnosis of psychiatric illness. Platelets have long been proposed as easily obtainable, neurological models of serotonergic neurons. This study examined whether a new measurement for platelet serotonin could aid in the diagnosis of postpartum depression and support the results from questionnaires. METHODS: Study participants included 11 patients with postpartum clinical depression according to the Diagnostic and Statistical Manual of Mental Disorders, fourth edition, criteria. Blood was donated either at acute onset of depression before treatment (n = 5) or while patients were nonresponsive to paroxetine treatment (n = 8; 2 of these patients dropped out). A follow-up sample was donated approximately 8 weeks later during paroxetine treatment (n = 11). Platelet serotonin was determined with a new immunocytochemical assay and standard high-pressure liquid chromatography. Serotonin levels were compared with Hamilton Depression Rating Scale scores. RESULTS: Platelet serotonin levels in patients with depression before paroxetine treatment or nonresponsive to their initial paroxetine regimen were reduced to 50% of normal levels. Treatment-induced severe reduction of platelet-associated serotonin only occurred in responsive patients. Mean platelet serotonin levels were significantly lower in responders (17.3%, standard deviation [SD] 4%), compared with nonresponders (33.4%, SD 8%; p < 0.001). CONCLUSION: Platelet serotonin levels obtained with a new immunocytochemical test correlated well with results from depression scoring and might be useful as evidence-based support for questionnaires.