Thank you for your inquiry. From what we gather from the question, you were asking about whether there is a type or strain of HIV that is not detected by the various HIV tests available.
There are two main types of HIV: HIV-1 and HIV-2. There are tests available that detect both types of HIV, such as the HIV-1/2 serology tests, but many tests, such as the HIV-1 PCR test, are solely for the use of detecting HIV-1. This is due to the high prevalence of HIV-1; approximately 95% of all HIV infections are caused by HIV-1, which can be divided into 4 main strains: M, N, O, and P (1). The group of HIV-1 that is responsible for the majority of HIV infections, group M, can be further divided into 9 distinct subtypes (1).
Although this may seem like too many different things for a simple test to detect, it is not! If someone acquires HIV, regardless of the strain or subtype, their body will start producing antibodies to the virus. Some of the antibodies produced will be similar enough to be detected by the same test, because even though the different HIV-1 strains and subtypes are genetically different, the viruses have certain parts that are essentially identical, and thus there will always be some identical antibodies produced.
It is important to note that HIV tests were specifically designed with the high variability of the HIV virus in mind. This also means that it is very unlikely that any new strain or subtype will not be detected by our current testing methods.
Recommendation: Refer to a healthcare professional for other health related questions.
AIDS Vancouver Helpline/Online, Marie
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1) HIV Strains and Types