Study type: Blood collected in a red-top tube; related body system: Circulatory/Hematopoietic and Immune systems.

HIV is the etiological agent of AIDS and is transmitted through bodily secretions, especially by blood or sexual contact. The virus preferentially binds to the T4 helper lymphocytes and replicates within the cells using viral reverse transcriptase, integrase, and protease enzymes. World Health Organization guidelines recommend that antiretroviral therapy (ART) should be offered to any person with HIV, regardless of CD4 test results or clinical stage, along with a discussion of the availability of daily oral pre-exposure prophylactic medications for patients considered to be at high risk for HIV infection. High-risk populations include gay and bisexual men, bisexual women, transgender people, sex workers, people who share IV needles contaminated with HIV-positive blood, people who receive HIV-positive blood products, and neonates who become infected in utero or during birth. Availability of postexposure prophylactic regimens should also be discussed as appropriate.

The process for obtaining specimens and communicating test results has changed dramatically since the disease was first identified. However, confirmed positive HIV findings continue to have a significant medical, psychological, and social impact on affected individuals and their potentially infected contacts. Test methods and algorithms have been developed to include as many potentially infected people as possible. Testing is available in a variety of settings, including the traditional laboratory (generally from blood specimens), specialty laboratories by mail (generally oral, finger stick, or urine specimens collected at home and mailed to the testing facility), clinical settings (using approved rapid-test kits in labor and delivery for emergencies), and nonclinical community-based screening sites (using either approved rapid-test kits or mail-in test kits). Accuracy of test results varies depending on specimen type, quality of collection technique, and test method.

In the traditional laboratory setting, initial HIV screening is generally performed using a combined immunoassay for HIV1 p24 antigen and antibodies to HIV1/HIV2. The antibody screening tests most commonly used do not distinguish between HIV1 and HIV2. A positive antigen/antibody screen may be followed by repeat testing by the same method, in duplicate, if recommended by the manufacturer. Otherwise, positive initial screens should be followed by an immunoassay that differentiates between HIV1 and HIV2 antibodies. A negative or indeterminate result for HIV1 obtained by HIV1/HIV2 differentiation testing could mean that the initial positive screen was related to the presence of HIV1 p24 antigen and the specimen was obtained after infection occurred but before the development of antibodies to the virus. Negative or indeterminate differentiation testing should be followed by a nucleic acid amplification test (NAAT or NAT) to determine whether HIV1 viral RNA is present. Positive HIV1 NAT results indicate acute HIV infection. The HIV screening test is routinely recommended as part of a prenatal work-up, unless the patient declines, and is required for evaluating donated blood units before release for transfusion.

The Centers for Disease Control and Prevention (CDC) has structured its recommendations to increase identification of patients who are infected with HIV as early as possible; early identification increases treatment options, increases frequency of successful treatment, and can decrease further spread of disease. The CDC recommends the following:

• Include HIV testing in routine medical care, and screen all patients between the ages of 13 and 64 years of age as part of routine medical care unless the patient requests to opt out.
• Implement new models to diagnose HIV infections outside medical settings; promote availability of rapid waived test kits such as OraQuick.
• Prevent new infections by working with persons diagnosed with HIV and their partners; adapt a voluntary opt-out approach that includes elimination of pretest counseling and consent requirements specific for HIV. General consents should cover all aspects of care.
• Perform initial testing for hepatitis B and C along with liver function tests. Co-infection may assist in determining the most appropriate selection of ART.
• Further decrease prenatal transmission of HIV by incorporating HIV testing as a routine part of prenatal medical care, and also perform third-trimester testing in areas with high rates of HIV infection among pregnant women.

HIV genotyping by polymerase chain reaction (PCR) methods may also be required to guide selection of medications for therapeutic regimens, investigate failure of therapeutic response to combination drug therapy, assess potential for drug resistance, and monitor for transmission of drug-resistant HIV. Genotyping for viral tropism should be used to determine eligibility before initiating treatment with a CCR5 co-receptor antagonist. Tropism testing should also be used to select alternate drugs once resistance to current drug therapy has been identified. An HIV tropism refers to the cell co-receptor used by the HIV-1 virus to penetrate the host cell and begin the infection. The discovery of two co-receptors used by the virus, either CCR5 or CXCR4 or both, to enter target CD4 cells led to development of CCR5 antagonists that block the virus from entering the cells. Genotyping for HIV-1 mutations in the integrase region of the viral DNA should be performed before initiation of therapy with integrase strand transfer inhibitors (bictegravir, dolutegravir, elvitegravir, raltegravir) in order to identify mutations that might compromise the selected therapy. Genotyping by PCR for the presence of the HLA-B*5701 mutation (inheritance pattern, autosomal dominant) should be performed before initiation of nucleoside analog reverse transcriptase inhibitor therapy (abacavir) as the mutation predisposes an individual to hypersensitivity reactions to abacavir or any abacavir-containing combination drug.

Molecular technologies are another approach to testing various specimen types; there are now numerous applications in the areas of pathogen identification (e.g., HIV), disease identification (e.g., oncology), and treatment development. Next-generation sequencing (NGS) is a category of molecular testing used to sequence DNA fragments. NGS technology is capable of sequencing DNA fragments from pathogenic organisms across a range in size from small sequences (single-nucleotide polymorphisms) to large sequences (thousands or billions). Multiplex assays are another type of molecular testing designed to simultaneously sequence DNA fragments from multiple pathogens to help identify mixed populations of infectious agents. The indications for NGS have expanded significantly and it is now an important tool in the diagnosis/identification of pathogenic organisms. NGS also provides a means and/or the potential to perform prognostic epidemiologic studies, lineage tracing (cell lines), discovery of genetic variants with drug resistance mutations, development of individualized therapeutic regimens, and development of preventive measures (e.g., vaccines).