Human Immunodeficiency Virus (HIV) is a retrovirus that causes Acquired Immunodeficiency Syndrome (AIDS). Untreated, AIDS causes the immune system to fail, making patients vulnerable to life threatening opportunistic diseases. HIV can diminish the health of a mother and baby. In the absence of intervention, about one quarter of neonates will acquire the virus from their mothers resulting in 400,000 new cases per year. In high-resource settings, the mother to child transmission rate is less than 1%.
Mechanism of Action
HIV tests detect antibodies or antigens of HIV in saliva, whole blood, or serum. Antibody tests are simpler and less expensive, but cannot detect the virus in the 3-12 week window between HIV infection and seroconversion. Among point of care antibody tests used in clinical settings, serum tests have highest sensitivity (99-100%) followed by whole blood tests (94-99%), followed by oral tests (86.5%). Unlike antibody tests, nucleic acid-based tests (NATs) directly amplify and detect the genetic material of the HIV virus, and can therefore detect infection around 12 days after exposure. NAT requires relatively complex machinery and skill, most suitable for batch screening of multiple samples in a centralized laboratory setting.
Current Use in High-Resource Settings
Most HIV screening in high-resource settings takes place in centralized laboratories. In the US, the algorithm includes both an ELISA and western blot test for serum antibodies. Results are typically available several days after a blood sample is drawn. Since 2001, 100% of US donor blood has been screened using NAT.
Application in Low-Resource Settings
Centralized laboratory services are not widely accessible in low-resource settings. Rapid, point of care HIV tests have become increasingly popular, with the vast majority of them detecting only antibodies. These disposable tests do not require power or other infrastructure, and are relatively easy to use. Once the finger has been pricked, blood is transferred to the test well using a disposable capillary tube. A few drops of chase buffer follow the blood sample onto the immunochromatographic strip. Test results are typically visible without any further equipment in 30 minutes or less. In many countries, the test is available at no charge to the patient, and especially to pregnant mothers coming for antenatal care.