To cut medical costs and diagnose minor ailments, WellPoint Inc. and Aetna Inc., among other health insurers, are letting millions of patients get seen online first. In a major expansion of telemedicine, WellPoint this month started offering 4 million patients the ability to have e-visits with doctors, while Aetna says it will boost online access to 8 million people next year from 3 million now.

The insurers are joining with companies such as Teladoc Inc., MDLive Inc. and American Well Corp. that offer virtual visits with doctors who, in some states, can prescribe drugs for anything from sinus infections to back pain. While patients with time constraints like the idea, some doctors say they worry that online visits may offer a higher potential for wrong diagnosis. A stomach ache may be nothing, or it could be appendicitis, said R. Adams Dudley, at the University of California, San Francisco.

"Just one little touch can make a big difference" to feel where the pain is at, said Dudley, a professor of medicine and health policy at the school. For symptoms doctors need to see, "some computer screens just don't have the best resolution, and you can't really adjust the lighting."