Question

A screen test for detection of human immunodeficiency virus (HIV) reveals a positive ELISA test. Which test will be used to confirm the diagnosis of HIV? A. Radioimmunoprecipitation assay (RIPA) test B. p24 levels C. Lymphocyte count D. Indirect immunofluorescence assay (IFA)

Short answer

Answer: The indirect immunofluorescence assay (IFA) test is commonly used to confirm the diagnosis of HIV after a positive ELISA test.

Step-by-step solution

Understand ELISA and its role in HIV detection

The enzyme-linked immunosorbent assay (ELISA) is a widely used method for detecting the presence of specific antibodies or antigens in a patient's blood sample. In HIV detection, the ELISA test is used to detect the presence of HIV-specific antibodies. A positive ELISA test means that HIV antibodies have been detected in the patient's blood, but it does not confirm the diagnosis of HIV. A confirmatory test is needed to ensure accuracy and to rule out false-positive results.

Review the given test options

A. Radioimmunoprecipitation assay (RIPA) test: RIPA is an immunoprecipitation technique that involves the use of radioactively labeled antigens to detect specific antibodies in a sample. It can be used as a confirmatory test for HIV, but it is not the most commonly used method. B. p24 levels: p24 is a protein found in the HIV virus. Measuring p24 levels can be helpful in detecting early-stage HIV infection, but it is not a confirmatory test for HIV diagnosis. C. Lymphocyte count: A decrease in lymphocyte count can be a sign of HIV infection since the virus attacks the immune system. However, this is not a specific test for HIV diagnosis, and it cannot be used as a confirmatory test. D. Indirect immunofluorescence assay (IFA): IFA is a method that uses fluorescently labeled antibodies to detect the presence of specific antigens in a sample. In the context of HIV, IFA can detect HIV-specific antibodies and can be used as a confirmatory test for HIV diagnosis.

Identify the best confirmatory test for HIV diagnosis

Based on the explanations above, the best test to confirm the diagnosis of HIV after a positive ELISA test is the indirect immunofluorescence assay (IFA), which is option D. This method specifically detects HIV antibodies and is widely used as a confirmatory test for HIV diagnosis. In conclusion, the correct answer to this question is option D. Indirect immunofluorescence assay (IFA).

Key concepts

Confirmatory Tests

When someone receives a positive ELISA test for HIV, it indicates the possibility that HIV-specific antibodies are present in the blood. However, to confirm the diagnosis of HIV and rule out any false-positive results, a second test is always required. This second test is known as a confirmatory test. Confirmatory tests are crucial because they ensure the accuracy of the initial screening test results. They are specifically designed to offer higher specificity and reliability.
Confirmatory tests for HIV include methods like the Western blot and the indirect immunofluorescence assay (IFA), which are employed to verify the presence of HIV-specific antibodies. These procedures closely examine the antibodies detected during the initial screening, confirming whether they are indeed HIV antibodies.

ELISA Test

The enzyme-linked immunosorbent assay, or ELISA test, is widely used as a primary screening method for detecting antibodies associated with the human immunodeficiency virus (HIV). It works by taking a small blood sample from the patient and applying it to a well that contains HIV antigens. If the patient's sample contains HIV antibodies, they will bind to the antigens in the well.
This binding reaction is detected by an enzyme that produces a color change, indicating a positive result. The ELISA test is advantageous because it is highly sensitive, meaning it can detect even low levels of antibodies. However, the possibility of false positives necessitates further confirmation with a more specific test to ensure an accurate HIV diagnosis.

Indirect Immunofluorescence Assay

The indirect immunofluorescence assay (IFA) is a highly specific confirmatory test used to verify the presence of HIV antibodies in a person's blood. This method involves applying the patient's blood sample to a slide containing immobilized antigens. If HIV antibodies are present, they will bind to these antigens.
To visualize this binding, a secondary antibody labeled with a fluorescent dye is added. This secondary antibody binds to any primary antibody present (e.g., the bound HIV antibodies). Under a fluorescence microscope, areas of fluorescence will indicate the presence of HIV antibodies.

• High specificity and accuracy: Because of its precision, the IFA is an excellent method for confirming positive HIV diagnoses.
• Detects specific antibodies: The assay is not only used for HIV but also for various other diseases that require antibody detection.

Overall, the IFA offers a reliable way to confirm the presence of HIV and ensures that initial screening results are indeed accurate.