Tuberculin testing: Its basis, methods, Tuberculin test and comparative results
DOUGLAS P. HAGEN, D.O. Kirksville, Mo.
Several procedures for administering test has converted to positive. Several methods tuberculin for skin testing of performing tuberculin skin tests will be re- viewed, and the results of the methods will be are reviewed. The Mantoux test is compared. considered the most accurate, in that the test dose can be measured Basis for tuberculin testing accurately, the equipment and During the first infection with the tubercle materials required are available readily, bacillus, the host acquires hypersensitivity to the organism. Hypersensitivity can be induced and the reactions can be read by the whole tubercle bacillus alone or a and recorded quantitatively. Its chief combination of the wax fraction of the or- disadvantage is the skill required ganism containing a lipopolysaccharide and to administer the test. Multiple-puncture tuberculoprotein but not by tuberculoprotein techniques need minimal skill alone. The reaction that occurs when an anti- for administration and false negative gen to tuberculosis is introduced intradermally provides a valuable testing procedure for both reactions are rare. However, the epidemiologic and case finding purposes. tuberculins are not well standardized, Tuberculin testing material is basically of the dose of tuberculin two types, old tuberculin (OT) and purified retained in the skin is unknown, and protein derivative (PPD). Old tuberculin is false positive reactions may a concentrated filtrate of broth in which tu- occur. Because of the variables affecting bercle bacilli have grown for 6 weeks. Cultures of Mycobacterium tuberculosis are heat-ster- the dose, quantitative measures ilized. The dead tubercle bacilli are filtered off, or reactions are only approximate guides and the filtrate is evaporated to 1/10 its orig- to degrees of sensitivity. inal volume. This material contains other con- stituents of tubercle bacilli and the growth medium. Efforts are being directed on a national basis Purified protein derivative consists of the toward elimination of tuberculosis from the active protein principle obtained from cultures United States. Tuberculin skin testing will of M. tuberculosis that have been grown play a part in achieving this goal. on synthetic media and extracted by neutral Tuberculin testing is performed for several ammonium sulfate precipitation. In 1952, a purposes. One is to aid in establishing the diag- large batch of PPD was produced as described nosis when signs and symptoms of the disease and adopted by the World Health Organization are noted. Another is for epidemiologic sur- (WHO) as the international standard tuber- veys of population groups to determine the culin, designated PPD-S.2 incidence and prevalence of the disease. A In about 1958 a batch of a new standard third is for case finding, which may involve PPD called RT 23 was prepared in Copen- case detection during surveys or follow-up of hagen for WHO. The batch was large enough contacts of patients in whom the disease has so it was anticipated that it would suffice as a been diagnosed recently or those whose skin standard until a PPD more specific than that