How to read PPD results
PPD (Purified Protein Derivative) is a skin test method used for tuberculosis screening and is widely used in the medical and health field. Many people have questions about the interpretation of PPD test results. This article will combine the hot topics and hot content on the Internet in the past 10 days to provide you with a detailed analysis of the meaning of PPD results and related precautions.
1. Basic principles of PPD testing
The PPD test determines whether you are infected with Mycobacterium tuberculosis by injecting tuberculin intradermally and observing the reaction at the injection site. The diameter of the induration, not the extent of redness and swelling, needs to be measured by a professional 48-72 hours after the test.
2. Judgment criteria for PPD results
According to the World Health Organization (WHO) and national guidelines, the criteria for determining PPD results are as follows:
| Induration diameter (mm) | Result judgment | clinical significance |
|---|---|---|
| <5 | negative | Not infected with Mycobacterium tuberculosis (except those with immunodeficiency) |
| 5-9 | Generally positive | Possible BCG vaccination or nontuberculous mycobacterial infection |
| 10-14 | Moderately positive | Indicates higher risk of tuberculosis infection |
| ≥15 | Strong positive | Highly suggestive of active tuberculosis |
3. Factors affecting PPD results
1.immune status: People with HIV infection and those who use immunosuppressants for a long time may have false negative results.
2.vaccination history: BCG vaccination may result in false positives.
3.other infections: Non-tuberculous mycobacterial infections may cause cross-reactivity.
4.operating factors: Injection technology, measurement error, etc.
4. Treatment suggestions after PPD is positive
| Crowd classification | Solutions |
|---|---|
| General healthy people | Recommended chest X-ray examination and close observation of symptoms |
| High-risk groups (such as close contacts) | Further examinations such as sputum examination and imaging are required |
| Strongly positive children | Recommend preventive anti-tuberculosis treatment |
5. Answers to recent hot questions
1.Does PPD conflict with the new coronavirus vaccine?
Recent studies have shown that COVID-19 vaccination does not affect PPD test results, and it is recommended that the interval be more than 4 weeks.
2.What situations require review?
A second test (boosting effect) may be performed when the first test result is negative but clinical suspicion is high.
3.What are alternative testing methods?
The gamma-interferon release test (IGRA) is more specific and suitable for BCG vaccinated people.
6. Precautions
1. Avoid scratching the injection site after the test
2. It is forbidden to wash the test area within 72 hours
3. The results must be judged by professional medical staff
4. A positive result does not mean a confirmed diagnosis of tuberculosis
Through the above display of structured data, I believe you will have a clearer understanding of the interpretation of PPD results. If the test result is abnormal, please seek medical advice promptly.
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