The **Anti-Parietal Cell Antibody (APCA) test** is a crucial diagnostic tool used primarily to identify autoimmune gastritis and pernicious anemia. The test detects specialized autoantibodies in the blood that mistakenly target and destroy the stomach's parietal cells. These cells are responsible for producing both hydrochloric acid and Intrinsic Factor (IF). Because Intrinsic Factor is essential for Vitamin B12 absorption in the small intestine, its deficiency leads to B12 malabsorption. Over time, this causes the characteristic megaloblastic anemia and potential neurological damage. A positive APCA result, combined with low B12 levels, is highly indicative of autoimmune-mediated pernicious anemia.

The **Anti-Ovarian Antibody (AOA) test** is a blood test that detects autoantibodies targeting ovarian tissue, such as the granulosa cells, oocytes, or the corpus luteum. The presence of these antibodies indicates an autoimmune response where the body's immune system mistakenly attacks its own ovaries.

This test is primarily used as a diagnostic tool in investigating Premature Ovarian Insufficiency (POI)—also known as premature ovarian failure—and unexplained female infertility. By identifying an autoimmune etiology for decreased ovarian function, the AOA test helps clinicians distinguish autoimmune-mediated tissue damage from other causes of reproductive dysfunction.

The **Antinuclear Antibody (ANA) test**—often mistakenly abbreviated as ADA—is a primary blood test used to detect autoantibodies that target the nucleus of a body's own cells. It serves as a vital screening tool for evaluating suspected systemic autoimmune disorders, most notably Systemic Lupus Erythematosus (SLE), Sjogren's syndrome, and scleroderma.

A positive ANA result indicates that the immune system is attacking its own tissues, though it requires further specific testing (like an ENA panel) and clinical evaluation to confirm a definitive diagnosis, as low levels of these antibodies can sometimes occur in healthy individuals.

The **Anti-Mullerian Hormone (AMH) test** is a blood test that measures the levels of AMH, a hormone produced by the small, growing follicles in a woman's ovaries. Because the amount of AMH in the blood directly corresponds to the number of remaining eggs, the test is widely used to assess a woman’s ovarian reserve (egg count).

This diagnostic tool is valuable in fertility planning, helping to predict responses to IVF treatments and evaluate conditions like Polycystic Ovary Syndrome (PCOS). Additionally, it can help estimate the onset of menopause or investigate early ovarian insufficiency.

The **Anti-Mitochondrial Antibody (AMA) test** is a specialized blood test used primarily to diagnose Primary Biliary Cholangitis (PBC), a chronic and progressive autoimmune liver disease. Mitochondria serve as the energy powerhouses within cells, but in patients with PBC, the immune system mistakenly produces autoantibodies that target these structures. This autoimmune attack causes inflammation and scarring of the small bile ducts inside the liver, potentially leading to liver failure if left untreated.

A positive AMA test—particularly the highly specific AMA-M2 subtype—is detected in approximately 90% to 95% of individuals with PBC, making it a definitive diagnostic marker.

**Anti-Infliximab Antibodies (ATIs)** are immune proteins produced by the body that mistakenly target and neutralize infliximab, a biologic medication used to treat autoimmune conditions like Crohn's disease and rheumatoid arthritis.

When a patient develops ATIs, the antibodies bind to the drug, clearing it from the bloodstream much faster than normal. This primary response leads to a significant drop in drug efficacy, often causing a return of disease symptoms (loss of response). Additionally, the formation of these immune complexes increases the risk of acute infusion reactions, such as fever, chills, or rashes, during treatment.
An Anti-Infliximab Antibodies (ATI) diagnostic test measures the level of these neutralizing antibodies in a patient's blood, typically alongside infliximab drug levels. This dual assessment, known as therapeutic drug monitoring (TDM), is crucial when a patient is losing response to treatment.

The **Anti-Hepatitis E Virus (HEV) IgM** test is a serological blood test designed to detect Immunoglobulin M (IgM) antibodies, which the body produces in response to a sudden, acute Hepatitis E virus infection.

Because IgM antibodies appear early during the initial phase of exposure and typically decline within a few weeks to months, a positive or reactive result serves as a strong diagnostic indicator of a current or very recent infection. Clinicians rely on this critical marker to differentiate acute illness from historical exposure (IgG) and to promptly manage or monitor acute liver inflammation.

The **Anti-Hepatitis E Virus (HEV) IgG** test is a serological blood test used to detect Immunoglobulin G (IgG) antibodies against the Hepatitis E virus.

A positive or reactive IgG result indicates that an individual has been exposed to HEV in the past. Because IgG antibodies develop during the recovery phase and persist in the bloodstream for years, they signify long-term immunity or a resolved, historical infection rather than an active illness. To diagnose an ongoing, acute Hepatitis E infection, clinicians evaluate these results alongside clinical symptoms, liver enzyme panels, and HEV IgM or HEV RNA PCR tests.

The **Anti-Hepatitis C Virus (HCV) Total** test is a primary screening blood test used to detect antibodies manufactured by the immune system in response to a Hepatitis C virus infection.

A "reactive" or positive result indicates exposure to the virus at some point in time, though it cannot distinguish between an active, ongoing chronic infection and a past infection that has cleared spontaneously or been successfully treated. Because these antibodies persist long-term, a positive total antibody screening must always be followed by an HCV RNA quantitative PCR test to confirm the current presence of the active virus.

The **Anti-Hepatitis B Envelope Antibody (AHBe) - Total** test (also known as the Anti-HBe or HBeAb test) is a crucial blood marker used to monitor and evaluate a Hepatitis B virus (HBV) infection.

This test detects total antibodies produced by the body’s immune system to target the Hepatitis B "e" antigen (HBeAg), a protein associated with active viral replication. A positive or reactive result generally signals "seroconversion"—meaning the immune system is gaining control, viral multiplication is slowing down, and the patient's infectivity (risk of transmitting the virus to others) has significantly decreased. Doctors use it alongside other HBV tests to determine the infection stage and assess treatment success.