The Human Immunodeficiency Virus (HIV) targets and weakens the body’s immune system, making individuals vulnerable to severe infections. HIV primarily attacks CD4 T-cells, which are the immune system’s main orchestrators, leading to a progressive loss of defense capability. Blood work is essential for managing this condition, confirming the infection, and continually monitoring its status and the effectiveness of treatment. Laboratory testing provides a quantifiable way to track the virus’s activity and its effects on the body’s health over time.
Blood Tests Used for HIV Diagnosis
Detecting HIV infection relies on specialized blood tests that look for the virus or the body’s response to it. The most common initial screening methods are combination antigen/antibody tests, which look for both HIV antibodies and a specific viral protein called p24. The p24 antigen appears in the blood sooner than antibodies after initial infection, allowing for earlier detection, typically between 18 and 45 days post-exposure.
Antibody-only tests are also used, particularly in rapid and at-home tests, but they generally require a longer window period of 23 to 90 days for reliable results. Nucleic Acid Tests (NATs) are the most sensitive method, directly searching for the virus’s genetic material (HIV RNA) in the blood. NATs can detect the virus as early as 10 to 33 days after exposure, but they are typically reserved for confirming initial positive results or for high-risk exposure cases due to their higher cost.
Primary Markers of Disease Progression
Monitoring the course of an HIV infection and the health of the immune system relies on two laboratory measurements: the CD4 T-cell count and the HIV viral load. The CD4 count is the most reliable indicator of immune function, as HIV specifically infiltrates and destroys these white blood cells. A healthy immune system typically maintains a CD4 count between 500 and 1,200 cells per cubic millimeter of blood. As the virus replicates, the CD4 count progressively declines, signaling a weakening immune defense.
A count that drops below 200 cells/mm³ is the clinical threshold used to define Stage 3 HIV (AIDS), indicating a severe risk of opportunistic infections. The viral load test measures the quantity of HIV RNA present in a milliliter of blood, indicating how actively the virus is multiplying. This measurement is expressed in copies/mL. The goal of treatment is to reduce this number to an “undetectable” status, meaning the virus is present at levels too low to be measured, often defined as less than 40 copies/mL.
These two markers are inversely related in untreated infection, meaning a high viral load generally corresponds with a low and declining CD4 count. Successful Antiretroviral Therapy (ART) rapidly drives the viral load down, which then allows the CD4 count to slowly rise as the immune system begins to rebuild its cell population. Achieving and maintaining an undetectable viral load is the primary objective of treatment, as it indicates the therapy is effectively suppressing the virus and minimizing the risk of disease progression.
Impact on Routine Complete Blood Count and Organ Function
Beyond the specific viral markers, HIV infection can alter routine blood tests, even independently of treatment effects. The Complete Blood Count (CBC) frequently reveals hematologic abnormalities due to the chronic nature of the infection. Anemia, characterized by a low red blood cell count or hemoglobin level, is the most common finding. The infection can also lead to leukopenia (a decrease in the total white blood cell count) and thrombocytopenia (a low platelet count).
These changes tend to worsen as the disease progresses and are associated with lower CD4 counts. HIV infection and associated conditions can also stress major organs, which is reflected in chemistry panels. Liver function tests (LFTs) may show abnormal readings, such as elevated liver enzymes like ALT and AST, often resulting from chronic inflammation or co-infection with hepatitis B or C. Kidney function is commonly monitored using serum creatinine and estimated glomerular filtration rate (eGFR), as chronic HIV can affect the kidneys and signal impairment.
Monitoring Health During Antiretroviral Therapy
Once a person begins Antiretroviral Therapy (ART), blood tests shift to monitoring both the therapy’s effectiveness and its potential side effects on the body. While the primary goal is viral suppression and CD4 recovery, monitoring involves tracking metabolic changes, as certain ART medications can affect how the body processes fats and sugars. Lipid panels are routinely checked to measure cholesterol and triglyceride levels, which may become elevated due to some regimens, increasing the risk for cardiovascular issues. Glucose monitoring is also performed to check for insulin resistance or the development of diabetes.
Additionally, kidney and liver function tests, including creatinine, eGFR, and liver enzymes, are regularly performed to detect any drug-related toxicity. If the viral load does not decrease as expected, specialized resistance tests, known as genotyping or phenotyping, may be performed to determine if the virus has developed mutations that make it resistant to the current medication regimen.