Farhad Majoo:

The Pap smear is the most effective cancer-screening test ever developed. When it was introduced in the United States in the 1940s, about 26,000 women died every of year of cervical cancer. Today, the exam—now known as the Pap test, since the modern method of preparation no longer requires smearing cells on a slide—is performed about 55 million times a year in this country, and about 120 million times annually worldwide. The effect of widespread, routine testing has been dramatic: Fewer than 5,000 American women now die each year of cervical cancer. If you account for population growth since the 1940s, the Pap test has reduced cervical cancer mortality by more than 90 percent.

The Pap test isn’t just good for women. It’s also a good business for doctors and diagnostic laboratories—maybe as much as a $500 million industry in the United States. The techs and doctors who look at Pap slides are the TSA agents of the medical world: They spend their days examining dozens of slides in search of tiny, subtle, and rare visual cues of disease. The process begins with a doctor collecting a sample of cells from a woman’s cervix. The cells are preserved in liquid, mixed with laboratory reagents, separated from blood and other biological material by centrifuge, and then deposited onto a slide. The cervical cells are examined first by cytotechnologists—specialists trained to analyze certain types of medical slides. If abnormalities are found, the Pap slides are then screened by pathologists, medical doctors who diagnose disease. Because the vast majority of Pap tests are performed on healthy women, about 90 percent of the slides seen by a typical lab are completely normal. The entire process costs about $25 to $100 per test, depending on the lab’s efficiency.