FRIDAY, May 16 (HealthDay News) -- A simple blood test to check levels of circulating tumor cells can help doctors more accurately assess how well treatments are working in women with metastatic breast cancer, according to a Georgetown University Medical Center study.

A blood test could be used to diagnose and assess the severity of certain mental illnesses, such as bipolar disorder, according to a new study. But some experts think this raises ethical concerns about prying into a person's mental status.

It may be possible to use a blood test to detect lung cancer, according to a Duke University Medical Center-led study.

Publishing in the Dec. 10 issue of the Journal of Clinical Oncology, researchers said a test for four blood proteins -- CEA, RBP, SCC and AAT -- may provide a simple follow-up for patients who've had suspicious chest lesions detected by imaging methods such as CT scan.