False-Positive and False-Negative Results Explained

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.

Why a result may need confirmation

Some tests are used to screen a large group, where a positive result may be followed by a more specific test. Other tests help a clinician evaluate symptoms or monitor a known condition. A negative result can lower the likelihood of what was tested for, but it may not exclude every cause of symptoms. An inconclusive result may mean the sample or measurement did not provide a clear answer. The next step, if any, depends on the test and clinical question.

What to do with a result

Start by checking which test was performed and what question it was meant to answer. Ask the ordering clinician whether the result is final, whether confirmation is customary, and whether timing or preparation matters. Mention relevant medicines and supplements and whether you followed preparation instructions. Do not assume that a positive screening result is a diagnosis, or that a negative result means symptoms should be ignored. If symptoms are severe or rapidly worsening, use local urgent or emergency care guidance rather than waiting for routine test follow-up.

What the journal evidence adds

A 2017 diagnostic-methods article in Jornal Brasileiro de Pneumologia explains sensitivity and specificity. These describe a test's performance under defined conditions, not the certainty of an individual person's diagnosis. The article's 2022 erratum corrects a table formula; this guide uses the basic definitions, not that numerical example.

Avoid turning the possibility of error into a reason to disregard every result. Instead, ask what the test was designed to detect, whether confirmation is usual, and what symptoms or timing affect the next step. A useful discussion can acknowledge uncertainty while still producing a clear follow-up plan. If comparing claims about two tests, check whether they were studied in similar populations and against an appropriate reference. A screening advertisement's accuracy percentage cannot, by itself, tell you your personal probability of disease.

Sources and further reading

• How to Understand Your Lab Results - MedlinePlus, U.S. National Library of Medicine. NIH consumer reference.
• How Cancer Is Diagnosed - National Cancer Institute. NIH consumer reference.
• Understanding diagnostic tests. Part 1 - Jornal brasileiro de pneumologia : publicacao oficial da Sociedade Brasileira de Pneumologia e Tisilogia (2017). diagnostic methods article.
• Erratum: Understanding diagnostic tests. Part 1 - Jornal Brasileiro de Pneumologia (2022). published correction; corrected specificity formula.

Health disclaimer

This article is for general education only. Its information and suggestions are not medical advice, diagnosis, or treatment and may not be right for everyone. Ask a qualified health professional for advice that fits your health, medications, and needs before changing your diet, exercise, supplement use, or care.