Today's Concept of the Tuberculin Test

¹ Associate Professor of Pediatrics, Baylor University College of Medicine
² Departments of Pediatrics and Medicine, Baylor University College of Medicine, and the Tuberculosis Division of Jefferson Davis Hospital (City and County)

(1) The tuberculin test is the most effective means of detecting tuberculosis in children. It is essential for early diagnosis and prevention of serious consequences of this disease.

(2) Recent studies on mycobacterial infections have provided better understanding of the tuberculin reaction. When a standard dose of 0.0001 mg. PPD is used, the size of the reaction carries great significance. A large reaction usually indicates a tuberculous infection, whereas a small reaction may or may not be tuberculous in origin.

(3) The specific tuberculin reaction caused by the tubercle bacilli is usually strongly positive. In differential skin testing, the standard tuberculin (PPD-S) usually gives a stronger reaction than the other mycobacterial antigens.

(4) The tuberculin cross reaction may be caused by a variety of non-tuberculosis mycobacteria. It is usually weakly positive. In differential skin testing, the homologous mycobacteria antigen usually gives stronger reaction than the standard tuberculin.

(5) When the standard tuberculin (PPD-S) is used alone, it is not always possible to distinguish between the specific reaction and the cross reaction by its size. Generally speaking, the stronger the reaction, the greater the likelihood of its being a specific tuberculin reaction.

(6) The multiple puncture tuberculin tests are useful for routine screening. However, because of lack of dosage control they are not recommended for diagnostic use. In areas where low-grade tuberculin sensitivity is prevalent, the Grade I (discrete papules) reactions should be classified as doubtful instead of positive, because many of them probably represent a cross reaction from nontuberculous infections.

(7) The patch test is much inferior to the Mantoux test because it may give both false positive and false negative reactions. When other methods cannot be used, the patch test may be utilized as a preliminary measure pending confirmation by the standard intradermal test.