Positive
Overview
Positive (Korean: 양성; 陽性, positive) is a test result indicating that a target substance, antibody, gene, condition, etc. has been detected or confirmed through a specific medical or scientific test or assay. Its opposite is negative (陰性, negative); when interpreting test results, one must consider not only the presence or absence of disease but also the test's sensitivity, specificity, and prevalence. It cannot simply be concluded that 'positive = disease present,' and the possibility of false positives and false negatives must always be kept in mind.
Key Concepts
Definition and Etymology
The term 'positive' (yangseong) comes from the Latin positivus and means that a particular reaction or signal is 'present.' Conversely, a case with no reaction or one below the threshold is called 'negative.' In addition to medical tests, it is used in various fields such as chemistry (e.g., Gram-positive bacteria), physics, and psychology (e.g., positive reinforcement).
Positive Results in Diagnostic Tests
In medical settings, positivity is determined through various methods such as blood tests, urine tests, imaging tests, and molecular diagnostics (PCR). For example, a positive RT-PCR test for coronavirus disease 2019 (COVID-19) means that viral RNA has been detected, while a positive antibody test is interpreted as evidence of an immune response from past infection or vaccination. HIV antibody tests, hepatitis B surface antigen (HBsAg) tests, and syphilis tests are also representative positive/negative tests.
Sensitivity, Specificity, and False Positives/Negatives
The key indicators for evaluating a test's reliability are sensitivity and specificity. Sensitivity refers to the proportion of people who actually have the disease who test positive, while specificity refers to the proportion of people who are actually healthy who test negative. The errors that can occur are as follows:
- False positive: A case that tests positive even though the disease is absent. Causes may include cross-reactivity of the test method itself, contamination, or reagent problems.
- False negative: A case that tests negative even though the disease is present. Causes include problems with the timing or method of specimen collection, or low viral concentration.
In particular, in populations with low prevalence, the false-positive rate becomes relatively higher, so it is common to perform an additional confirmatory test. Using Bayes' theorem, the positive predictive value (PPV) can be calculated.
Positivity in Infectious and Chronic Diseases
In infectious disease diagnosis, a positive result serves as the starting point for isolation, treatment, and epidemiological investigation. In the case of tuberculosis, if a tuberculin test or interferon-gamma release assay (IGRA) is positive, chest X-ray and sputum tests are used for confirmation. In cancer screening, a positive result for a tumor marker (e.g., PSA, CA-125) does not necessarily mean cancer, and a biopsy is used for final confirmation.
Positivity in Science and Chemistry
In microbiology, bacteria are classified as Gram-positive or Gram-negative according to the results of Gram staining. In chemistry, the appearance of a reaction with a specific reagent is called a 'positive reaction'; for example, urine tests determine whether proteinuria, hematuria, or glucose are positive. In psychology, a stimulus that reinforces behavior, such as a reward or praise, is called a 'positive reinforcer.'
Recent Trends
In 2024–2025, AI-based diagnostic support systems are contributing to improving the accuracy of positive determinations. Research is active on deep learning models detecting pulmonary nodules or pneumonia opacities on chest X-ray and CT images to reduce false positives and false negatives. In addition, with the spread of rapid antigen tests (RAT), the proportion of individuals checking their own positivity has increased, and the importance of result reporting systems and linkage to confirmatory testing has grown accordingly. Furthermore, genetic-based liquid biopsy is developing in the direction of improving positive predictive value in early cancer diagnosis, and result delivery guidelines are being emphasized to ease the psychological impact of the word 'positive' when explaining test results to patients.
Related Topics
- [[위양성]] (false positive)
- [[민감도와 특이도]] (sensitivity and specificity)
- [[PCR 검사]] (PCR test)
- [[감염병 진단]] (infectious disease diagnosis)
- [[그람 염색]] (Gram staining)
- [[양성평등]] (gender equality)