Invasive tests
Invasive tests are medical procedures designed to gather diagnostic information by penetrating the body's defenses, which include skin, sphincters, and various reflex systems. These tests are typically employed when noninvasive options are insufficient, and they can provide critical insights into a patient's health. Common types of invasive tests include biopsies, lumbar punctures, and endoscopies, which allow for the collection of tissue or fluid samples directly from affected areas. Procedures like amniocentesis and thoracentesis are examples of fluid aspiration tests used in prenatal care and to assess abnormalities in body cavities, respectively.
Despite their benefits, invasive tests carry inherent risks, such as infection, which is mitigated through sterile techniques. As medical technology progresses, some traditionally invasive tests have become less so, improving patient safety and comfort. Ultimately, while invasive tests can involve discomfort or pain, they are vital in diagnosing conditions that might otherwise go undetected.
Invasive tests
Anatomy or system affected: All
Definition: Tests that require the passage of an instrument through the body’s protective barriers
Indications and Procedures
Skin, sphincters, and gag- and cough-reflex systems are some of the defenses that can be penetrated to gather important diagnostic information. Invasive tests provide medical insights that are unattainable by noninvasive or laboratory tests. Invasive tests are typically performed last in a diagnostic protocol because penetration of the body's defenses is not without risk. An anesthetic agent is commonly used to minimize any discomfort or pain that may arise during the tests. Although invasive, these tests often circumvent the trauma of exploratory surgery.
In general, invasive tests may be classified as those that allow the physician to obtain samples of fluid, tissue, or tumors directly from their site of origin through aspiration, lumbar puncture, or biopsy, or those that allow direct viewing of specific areas of the body through endoscopy. Some test procedures allow both direct viewing and sample collection; bronchoscopy is one such procedure.
One of the more familiar aspiration tests is amniocentesis. Amniocentesis involves removing twenty to thirty milliliters of fluid from the amniotic sac for analysis. This test is used in prenatal care between weeks fifteen and eighteen to assess the genetic makeup of the fetus or to detect developmental abnormalities.
Fluid from effusions can also be aspirated for analysis. Effusions are collections of an abnormally large quantity of fluid within a serous or synovial cavity. While a small amount of fluid is normal in these cavities, a large amount indicates a pathology that should be identified and treated. Once an effusion is tapped, the fluid is grossly examined for color and for clarity or turbidity. Microscopic investigations of the fluids are performed to assess the types of cells present, such as immune cells or malignant cells, and to identify microorganisms that may be present. Paracentesis is the removal of fluid from effusions within the abdominal, or peritoneal, cavity. If the effusion in this region is large, it is called ascites. Removal of fluid from the lung cavity, called thoracentesis, requires penetration of the chest wall between the ribs (intercostal spaces). Common causes of effusions include infections, congestive heart failure, kidney disease, and malignancy.
Synovial fluid is most commonly aspirated from the knee, but other joints can also be investigated in this manner. Red blood cells, inflammatory cells, or crystals may be identified by microscopic evaluation of the aspirated fluid. Osteoarthritis, rheumatoid arthritis, and gout are some diseases that can be diagnosed through synovial fluid aspiration.
Cerebrospinal fluid (CSF) is housed within the bony cranium and spinal column. Fluid from this space is collected by lumbar puncture (spinal tap) when viral, bacterial, or fungal meningitis is suspected. Lumbar puncture may also be performed when a tumor or leukemia of the central nervous system is suspected or to determine whether a subarachnoid hemorrhage is present.
Fine-needle aspiration (FNA) is a specific kind of percutaneous (through-the-skin) needle biopsy. FNA can be used to collect a sample of cells from any palpable mass. By directly inserting a needle into the mass and then washing, or flushing, the region, some cells can be eroded from the tissue surface. These cells are set adrift in the fluid, which is sucked back into the flushing syringe. Microscopic evaluation of the cells can then be performed. Breast, neck, abdominal, and lymph nodes are some of the places where FNA is utilized.
Alternative biopsy techniques include gently scraping off a small surface, as in the Papanicolaou (Pap) testing of the cervix, or removing a deeper tissue sample, as in the punch biopsy of the cervix. Biopsy can sometimes require small surgical incisions to reach a certain organ, such as muscle, skin, breast, bone, or renal (kidney) biopsy.
Tissue biopsies may be taken directly from an organ without surgical incisions; one way to do this is with endoscopy. Typically, endoscopes are flexible probing instruments fitted with fiber-optic viewing devices. Often, a tool attachment allows the use of tiny cutting and sampling devices. Small pieces of tissue can be removed from some otherwise inaccessible areas of the body. Different kinds of endoscopes are used to accommodate the unique structural features of body regions, such as the bronchi, stomach, or colon. Sterile techniques are implemented in all cases.
Bronchoscopy is utilized in diagnosing pulmonary infections and lung cancers or in locating and removing foreign objects found in the airways. Esophageal gastroscopy is used to determine the source of upper gastrointestinal problems, such as gastric or peptic ulcers, esophageal varices, esophageal reflux, or malignancy. Colonoscopy is similarly used to evaluate the origins of lower gastrointestinal problems. Colon polyps can be identified, and the mucosal lining of the colon can be evaluated for ulcerative colitis, diverticula, or adenocarcinomas.
Finally, arteriography (including angiography) and cardiac catheterization are important and frequently used invasive tests. These tests are used to evaluate the cardiovascular system. Angiography combines radiographic techniques with the injection of dyes into arteries. This combination allows the physician to determine whether an artery is blocked (occluded). Angiography is particularly useful in patients who have heart conditions, such as angina, and can be used to evaluate renal (kidney) arteries, aortic dissection, or cerebral aneurysms. The result of arteriography is a critical component in determining whether surgery or drug intervention is best for a given patient.
As a diagnostic tool, cardiac catheterization provides insight into the health of a heart. Pictures of the heart can be taken as the catheter is advanced into first the right side and then the left side of the heart. A dye is injected into the heart so that the flow can be traced as the heart pumps. The heart chambers, valves, and blood vessels can be evaluated. Additionally, pressures within the heart chambers can be recorded.
Uses and Complications
The greatest health risk with any invasive test is infection. For this reason, sterile methods are used to keep infections and mortality caused by infections to a minimum. With proper care, the risks of invasive testing are surpassed by the benefits of the early and proper diagnosis that such tests provide. As medicine advances in the twenty-first century, some tests which have historically been invasive have become less so with the invention of new technology and a deeper understanding of the human body.
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