False Positive and False Negative
Definition
No test is perfect. There are two types of incorrect results:
| Result | What it means |
|---|---|
| False positive | The test says the disease or condition is present, but it actually is not |
| False negative | The test says the disease or condition is not present, but it actually is |
Purpose
Knowing these two concepts determines how a single test result should be approached. Results are usually correct; incorrect results are not common but are more likely with certain types of tests or when a test is not performed correctly.
Results
If a result is suspected to be incorrect, the test may need to be repeated.
This concept is central to screening tests. A screening test assesses risk in a person without symptoms; a diagnostic test confirms or rules out a condition in a person with symptoms. A positive screening result does not mean the person has that disease, it only shows that the risk is higher than average. Screening tests are estimates; they can give false positives and false negatives. A definitive answer requires a confirmatory diagnostic test.
Risks and Limitations
Many terms in this glossary have concrete examples of false positives or false negatives, for example an elevated D-dimer having many causes besides a clot, a negative rapid antigen test not ruling out disease, or positive ANA and rheumatoid factor being seen in healthy people.