Medical test

A medical test is a specific procedure used to find, identify, or track diseases. Healthcare providers use these tools to understand disease processes or a person's susceptibility to illness. They also use tests to determine the best course of treatment for a patient. Medical tests are typically performed in professional medical settings. These procedures can range from simple visual exams to complex chemical and cellular analyses.

By using these tools, doctors can move from guessing to knowing about a patient's health.

Medical tests are classified by their primary purpose into three main categories. The first is diagnostic testing, which is used to confirm a disease in someone showing symptoms. For example, a doctor might use nuclear medicine to examine a patient suspected of having lymphoma. They might also measure blood sugar in a person with increased urination to check for diabetes mellitus. The second category is screening, which looks for disease in at-risk groups or populations. This includes newborn screening for congenital hypothyroidism by measuring TSH levels in the blood. A third category is monitoring, which tracks how a patient responds to a specific medical treatment.

There are several distinct methods used to conduct these tests. Patient observations might include photographs or recorded medical histories. Physical examinations are another common method used to detect signs of illness. Radiologic tests use tools like x-rays to create images of a body target. These often require a contrast agent to make the images clearer. Some tests are performed in vivo, which means they happen inside the living body. An example is manometry, which uses a catheter to test the colon. Other in vivo methods involve administering a diagnostic agent to measure a body's response, such as an oral food challenge.

Many tests are performed in vitro, meaning they happen outside the living body. This involves testing a sample of tissue or bodily fluids. Common samples include blood, urine, stool, and sputum. In these samples, scientists might perform microbiological culturing to find pathogenic bacteria. They may also perform genetic testing or check for electrolytes like sodium, potassium, creatinine, and urea. These in vitro tests allow for precise chemical and molecular diagnostics in a controlled laboratory setting.

When evaluating a test, scientists look at accuracy and precision. Accuracy refers to how closely a test result matches the true value. Accuracy is maximized by calibrating equipment with reference material and using quality control programs. Precision is the ability of a test to produce the same result when repeated on the same sample. An imprecise test will yield widely varying results during repeated measurements. Laboratories monitor precision by using specific control materials to ensure consistency.

Test results are often reported as positive or negative. In a binary classification, a positive result means the parameter being evaluated was present. A negative result means the parameter was absent. It is important to note that a negative result is not always bad news. For example, a negative screening test for breast cancer is actually a very positive outcome for the patient. Some tests also provide quantification, which measures exactly how much of a substance is present. A blood test might provide a specific mass concentration of a target entity.

Doctors must carefully consider the indications and contraindications for every test. An indication is a valid medical reason to perform a test, such as a cholesterol test for a middle-aged person. A contraindication is a valid reason to avoid a test. If a person recently had the same test, that recent result might be a contraindication. Doctors aim to ensure the net benefit of a test is greater than the potential harm. This calculation includes the benefits of changing an intervention versus the harms of the test itself or its side effects. They also consider practical factors like cost, time, and the availability of resources.