Medicine: Unbelievable Blood Tests

Medical testing centers have plenty of business these days -- perhaps more than they can properly handle. Prompted by fears of everything from AIDS and Lyme disease to high cholesterol, record numbers of people are lining up to give a blood sample and get back the good news, or bad. Too frequently, though, the news is just plain wrong. Several recent studies have revealed disturbing sloppiness or simple error in the way some blood tests are conducted and interpreted.

Among the worst offenders are public cholesterol-screening programs. Such centers, already a familiar sight in supermarkets and shopping malls in some parts...