Is it possible to have a 100% accurate AIDS test result?

First, that depends on what you consider 100% accurate. In epidemiology, there is a concept for screening tests called sensitivity and specificity. Sensitivity is the percentage of people who are positive that will test positive. Specificity is the percentage of people who are negative who will test negative.

A test that is 100% sensitive will never miss a person who has HIV (the virus that is tested for is Human Immunodeficiency Virus, not the disease it causes AIDS-Acquired Immunodeficiency Syndrome) but it will also probably have a number of false positives. Inversely, a test that never has a false positive would probably miss quite a few true positives.

For this reason, a second set of calculations is used to evaluate the worth of a test called positive predictive value (PPV) and Negative Predictive Value (NPV) that are given a percent. The PPV is the percent of occurrences when an individual that tests positive that they actually are positive. Inversely, NPV is the percent of negative test results that do not have HIV.

These values can vary greatly depending on the population you test. For example, if you have a high prevalence of HIV in the population, a test may have good PPV and NPV, but if you have a low prevalence of HIV, the test may identify too many false positives and therefore have a low PPV.

With this in mind, there is a test for HIV that is considered very accurate called a western blot. This test screens for viral genetic products rather than viral proteins like the commonly used ELIZA (Enzyme Linked ImmunoSorbent Assay) test. Unfortunately, a western blot is not as quick to run as an ELIZA test and is much more expensive. Because of this, it is usually only used to confirm positive results.

In addition, there is the human factor when running these tests. People running the tests or manufacturing and delivering the testing supplies are bound to make a mistake eventually. Even if a test has 100% PPV and 100% NPV, mistakes could produce a false result.

I would say no, because you can never totally eliminate factors such as tech error (during testing), flaws in the test method itself, poor blood draws, and so forth. Think of the accuracy of HIV testing, or any medical testing, as a curve gradually increasing but never reaching 100% - I hate to use a calculus analogy but it fits.