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 20 to 30 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.

Another common biopsy method, core needle biopsy, uses a larger needle than the FNA, allowing for a wider range of use depending on the pathology suspected. It is less invasive than surgical biopsies and offers relatively quick results. Sometimes, biopsies are guided by imaging tools, such as ultrasound, stereotactic X-ray, or a computerized tomography (CT) scan. This aids medical practitioners when taking a biopsy from areas that are difficult to reach.

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. Capsule endoscopy using a swallowable camera can also be used to investigate and diagnose gastrointestinal problems.

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 heart health. Pictures of the heart can be taken as the catheter is advanced into 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 minimize infections and mortality caused by infections. With proper care, the risks of invasive testing are outweighed by the benefits of early and accurate diagnosis that such tests provide. As medicine advances in the twenty-first century, some tests that have historically been invasive have become less so with the invention of new technology, imaging techniques, and a deeper understanding of the human body.

Bibliography

“Biopsy.” MedlinePlus, 2 May 2017, medlineplus.gov/biopsy.html. Accessed 19 Sept. 2025.

Cavanaugh, Bonita Morrow. Nurse’s Manual of Laboratory and Diagnostic Tests. 4th ed., F. A. Davis, 2003.

Chandrasekhara, Vinay, et al. Clinical Gastrointestinal Endoscopy . 4th ed., Elsevier, 2025.

Dabbs, David J. Breast Pathology. 3rd ed., Elsevier, 2024.

"Diagnostic Tests/Procedures ." Yale Medicine, www.yalemedicine.org/clinical-keywords/diagnostic-testsprocedures. Accessed 19 Sept. 2025.

Dugdale, David C., et al. “Cerebrospinal Fluid (CSF) Analysis.” MedlinePlus, 13 Mar. 2025, medlineplus.gov/lab-tests/cerebrospinal-fluid-csf-analysis. Accessed 19 Sept. 2025.

“Endoscopy.” MedlinePlus, 3 Mar. 2023, medlineplus.gov/ency/article/003338.htm. Accessed 19 Sept. 2025.

Fischbach, Frances Talaska, et al. Fischbach’s A Manual of Laboratory and Diagnostic Tests. 11th ed., Wolters Kluwer, 2022.

Griffith, H. Winter. Complete Guide to Symptoms, Illness, and Surgery. Revised and updated by Stephen Moore and Kenneth Yoder, 6th ed., Perigee, 2012.

Pagana, Kathleen Deska, and Timothy J. Pagana. Mosby’s Diagnostic and Laboratory Test Reference. 17th ed., Elsevier, 2024.

Ravin, Carl E., editor. Imaging and Invasive Radiology in the Intensive Care Unit. Churchill Livingstone, 1993.

Van Leeuwen, Anne M., and Mickey Lynn Bladh. Davis’s Comprehensive Manual of Laboratory and Diagnostic Tests with Nursing Implications. 11th ed., F.A. Davis, 2025.

Zaret, Barry L., et al., editors. The Yale University School of Medicine Patient’s Guide to Medical Tests. Houghton Mifflin, 1997.