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Laboratory Diagnosis of HIV Infection



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Predictive Value: Single Screening Test

Slide 11

October 2009

I do wish to stress that if one uses the rapid screening antibody test in a population with low prevalence of HIV infection, such as those with HIV prevalence of <5%, the positive and negative predictive value is related to the prevalence of a particular disease. So, for example, if HIV prevalence is 1% in a population that the laboratory serves, then despite having a good sensitivity and specificity of the test, the positive predictive value (meaning that a positive result indicates true positive) is only 83% indicated in this table. And, in many communities in the United States where the prevalence is 0.1% or less (meaning less than 1 in 1000 has HIV infection), the positive predictive value is only 33%, so it's actually less accurate than a flip of a coin.

Single Screening Test

 


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