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June 21, 1985

Screening for HTLV-III Antibodies: The Relation Between Prevalence and Positive Predictive Value and Its Social Consequences

Author Affiliations

American Red Cross Blood Services Los Angeles-Orange Counties Region

JAMA. 1985;253(23):3396-3397. doi:10.1001/jama.1985.03350470047009

To the Editor.—  The article by Weiss et al1 concerning human T-cell leukemia (lymphotropic) retrovirus type III (HTLV-III) antibody testing published in the Jan 11 issue of The Journal fails to draw the crucial distinction between the use of the test in a diagnostic setting and its use in screening large populations of asymptomatic individuals such as blood donors. The authors neglect to mention that the predictive value of a positive test result (ie, the likelihood that a reactive laboratory test result represents prior exposure to HTLV-III) is dependent not only on test sensitivity and test specificity, but is even more closely related to the prevalence of the disease state in the tested population. We can estimate the prevalence of HTLV-III exposure in blood donors from three pieces of data: (1) the 1983-1984 incidence of the acquired immunodeficiency syndrome (AIDS) in non—risk group individuals has been estimated at one