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Understanding Medical Test Accuracy: False Positives and Negatives
When a test comes back positive or negative, it's tempting to take the result at face value — as if medical tests were infallible truth machines. In reality, all diagnostic tests have limitations. ...
Medically reviewed by Dr. Emily Johnson · Editorial Policy
When a test comes back positive or negative, it's tempting to take the result at face value — as if medical tests were infallible truth machines. In reality, all diagnostic tests have limitations. They can give wrong answers — both falsely reassuring (saying you don't have something you do) and falsely alarming (saying you have something you don't). Understanding how test accuracy works is one of the most important and least-taught concepts in health literacy.
The Core Concepts: Sensitivity And Specificity
Two fundamental measures describe how well a diagnostic test performs:
Sensitivity: The ability of a test to correctly identify those who HAVE the disease — the true positive rate. A sensitive test misses few cases. High sensitivity = few false negatives. If a test is 95% sensitive, it correctly identifies 95 out of 100 people with the disease, but misses 5 (false negatives).
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understandingmedicaltestaccuracygeneral health
Primary Source
NIH MedlinePlus — Medical Tests: Understanding ResultsMedical Disclaimer: This article is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of your physician or other qualified health provider with any questions you may have regarding a medical condition.
About the Author
Dr. Emily Johnson
AI Nutritionist & Dietitian
Dr. Emily Johnson is Caraly's nutrition and dietetics educator, bringing evidence-based guidance on diet, weight management, sports nutrition, food allergies, and the science of eating well. Her content is developed in alignment with guidelines from the Academy of Nutrition and Dietetics (AND), the Harvard T.H. Chan School of Public Health, and the CDC's dietary recommendations. In a landscape crowded with fad diets and conflicting nutritional advice, Dr. Johnson's mission is to cut through the noise and present what peer-reviewed research actually shows — with primary source citations in every article.
Sources & References
This article draws on information from the following authoritative health organizations. Always consult a qualified healthcare professional for personal medical advice.
- 1NIH MedlinePlus — Medical Tests: Understanding Results
- 2Mayo Clinic — Medical Tests: Sensitivity and Specificity
- 3Johns Hopkins Medicine — Understanding Diagnostic Tests
- 4Cleveland Clinic — False Positive and False Negative Test Results
- 5Harvard Health — Understanding Medical Tests: Sensitivity, Specificity, and Predictive Value