Because doctors have not traditionally screened patients for the virus, many people do not even know they are infected until their livers show signs of serious damage.

Until now, doctors have not routinely screened people for lung cancer because X-rays could not detect tumors in time to cure them, or significantly prolong patients' lives.

If doctors can screen for autism and mental retardation at birth, scientists say, affected babies could be given special early enrichments or drugs designed to help their brains develop more normally.

A recommendation being considered by the federal Centers for Disease Control and Prevention urges doctors to routinely screen every patient ages 13 to 64.

But the results suggest that doctors should screen the families of children facing surgery to see if there are members who smoke.

Given this, the study says, doctors who suspect their patients have been exposed to carbon monoxide should screen them for heart muscle damage, and the patients should be monitored.

Dr. Shafer said most doctors routinely screen sexually active young women for chlamydial infections, but do not do so for young men.

Under a procedure known as preimplantation genetic diagnosis, doctors screen embryos for a high risk of developing breast cancer or arthritis, and implant only embryos with the desired genetic makeup.

Results could indicate whether doctors should routinely screen for Lyme disease in endemic areas, he said.