Each year about 4 million Americans receive blood transfusions, and despite screening for hepatitis, thousands of cases of transfusion-related hepatitis occur.

Until recently, blood banks have been unable to prevent the transmission of the disease, because there has been no blood test for the virus that causes it--newly discovered hepatitis C virus. In the past year, however, a test allowing the screening of blood for hepatitis C virus was approved by the Food and Drug Administration. The test--used in blood banks--promises to reduce the cases of hepatitis C in Los Angeles County, where as many as 1 in 200 adults are infected with the virus. Most of those afflicted, however, acquired the infection from sources other than transfusions, usually from sexual intercourse.

Even with this test and the screening tests for other types of hepatitis and AIDS, the risk of contracting HIV, the virus that causes AIDS, is 1 in 104,000 in the Los Angeles area, according to the Red Cross. The odds are lower for contracting hepatitis C. They are estimated to be 1 in 300 to 1 in 1,000. Thus, if you plan to undergo elective surgery, you may want to arrange with your doctor to store your own blood for later use. If that is not possible, you might consider using "donor-directed" blood from someone of your choice.