Screening vs Diagnostic Tests & Follow-Up Questions

A false-positive result suggests that a condition or substance is present when it is not. A false-negative result suggests that it is absent when it is actually present. These terms describe possible test errors; they do not tell you that a particular result is wrong. How likely an error is depends on the test, the condition being assessed, when and how the sample was collected, and the person's circumstances.

A mammogram is an X-ray image of the breast. It can be used to screen people who do not have symptoms or to evaluate a specific concern. The test and follow-up depend on the reason for imaging, age, personal risk, prior results, and local clinical guidance.

A colonoscopy uses a flexible tube with a camera to examine the rectum and colon. NIDDK says clinicians may use it to investigate symptoms such as rectal bleeding, changes in bowel movements, abdominal pain, or unexplained weight loss. It is also used to screen for colon polyps and colorectal cancer. The reason for the test affects how a clinician interprets what is found.

Lung function tests, also called pulmonary function tests, measure how well air moves in and out of the lungs and how the lungs exchange gases. Spirometry is a common type: you breathe in deeply and blow into a mouthpiece, and the device measures how much air you exhale and how quickly. Other tests may measure lung volumes, gas transfer, or breathing during exercise. A clinician selects a test based on symptoms and the question being evaluated.