Question

Enzyme immunoassay (EIA) tests are used to screen blood specimens for the presence of antibodies to HIV, the virus that causes AIDS. Antibodies indicate the presence of the virus. The test is quite accurate but is not always correct. Here are approximate probabilities of positive and negative EIA outcomes when the blood tested does and does not actually contain antibodies to HIV:

A) Provide the probabilities for positive and negative EIA outcomes.
B) Describe the accuracy of the EIA test.
C) Explain the mechanism of EIA testing.
D) Analyze the implications of false-positive EIA results.

Answer 1

EIA tests are used to detect HIV antibodies with a high degree of accuracy, employing antibodies linked to enzymes. Though EIA tests are accurate, false positives can occur and are typically confirmed with additional, sensitive tests like western blots or NAATs.

Step-by-step explanation:

Enzyme immunoassay (EIA) tests are critical in screening for the presence of antibodies to HIV, indicating potential exposure to the virus. The accuracy of these tests is high, usually with a false-positive rate around 0.5%. The EIA operates by using a detection antibody that attaches to a specific antigen with high specificity. This antibody is linked to an enzyme that, when a substrate is added, creates a colored product if the antigen is present, indicating a positive result. False positives can occur, often due to cross-reactivity with antibodies from other infections. Consequently, a positive EIA test is typically validated with a confirmatory western blot or a nucleic acid amplification test (NAAT) to ensure accuracy.

EIAs generally involve multiple layers of antibodies that capture the antigen of interest, such as HIV peptides in the case of HIV screening. These tests can be performed in microtiter plates and use antibody-enzyme conjugates that interact with a substrate to produce a visual or quantifiable signal.
While EIA tests are careful to eliminate cross-reactive antibodies, false positives can have profound implications, such as psychological stress and unnecessary follow-up testing. To avoid such consequences, confirmatory tests like western blot or NAAT are employed whenever a positive EIA result is obtained.