Which of the following tests is commonly used to test for HIV?

The ELISA test is commonly used to test for HIV because it is specifically designed to detect antibodies to the HIV virus in the bloodstream. This test is based on enzyme-linked immunosorbent assay technology, which allows for the quantitative measurement of these antibodies, making it an effective screening tool for HIV infection.

The ELISA test is particularly advantageous as it is sensitive and can process multiple samples at once, providing timely results for individuals being screened. In the context of HIV testing, a positive ELISA result typically requires confirmation with a more specific test, such as the Western blot test or a PCR test, ensuring both accuracy and reliability in diagnosis.

Other tests listed do not serve the purpose of screening for HIV. Acid fast stains are used primarily in the diagnosis of tuberculosis and other mycobacterial infections. Pulmonary function tests assess the respiratory system's efficiency but do not pertain to infectious diseases like HIV. A complete blood count measures various components of blood but does not specifically test for the presence of the HIV virus or its antibodies. Therefore, the ELISA test stands out as the direct and specific method for HIV detection.