The 48-hour ppd skin test can basically determine the results. The diameter of the mass is negative within 5 mm; Positive within 5-20mm; More than 20 mm strong positive.
Introduction to PPD:
Tuberculin test, also known as PPD test, usually takes 48-72 hours to observe. Erythema was observed 72 hours after intradermal injection of tuberculin reagent. If the diameter of erythema
If erythema >: 2cm, or blisters, ulcers, induration, etc. It suggests that PPD test is strongly positive, suggesting that tuberculosis infection may occur. However, PPD test is not a definite test to diagnose tuberculosis, and further culture of tuberculin is needed to make a definite diagnosis.
Refer to the above content: Baidu Encyclopedia-Tuberculin