سؤال: Q. What can cause a false-positive result in an HIV antibody ELISA test? A. There are many reasons for a false-positive ELISA result. Some of the more common reasons for a false positive are: Contamination: In a laboratory, samples may be placed in the wrong testing well; wells containing negative samples may be contaminated from adjacent positive wells; plate washers may malfunction. In addition, treated blood and blood abnormalities have been implicated in false positive reactions. False positive reactions have been reported in 19% of people with hemophilia, 13% of alcoholic patients with hepatitis, and 4% of hemodialysis patients. Pregnancy. If this is not her first pregnancy, a woman may react positively when she is, in fact, negative. History of injection drug use. Cross-reactivity with other retroviruses. Q. What is the expected false-positive rate for an HIV antibody ELISA? A. The false-positive rate is 1 to 5 per 100,000 assays.