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 356/67 Journal AOA/vol. 70, December 1970 Tuberculin testing presently available could be developed. This tration and tissue induration. The reaction new PPD RT 23 was assayed against PPD-S is not associated with circulating antibodies. and other batches of PPD used in international and cannot be transferred passively by means work. Two reasons for preparing the large of serum, although it sometimes can be trans- batch of PPD were to make it unnecessary ferred passively by means of cells. to standardize new batches and to increase the When tuberculin testing is carried out, there comparability of data obtained by tuberculin is no immediate reaction to the intracutaneous testing in different areas for different periods.3 injection of tuberculin. Induration and er- The amounts of tuberculin used have been ythema develop hours after the injection of measured both in tuberculin units (TU) and the material intracutaneously. The reaction by the weight of the material. Although the continues to increase in magnitude for from WHO committee has decided to abandon the 24 to 72 hours. tuberculin unit and substitute weight of ma- terial, doses are still referred to in the United Methods States as first strength (0.00002 mg./0.1 ml., Several testing procedures are available for 1 TU) ; intermediate strength (0.0001 mg./0.1 the administration of tuberculin for skin test- ml., 5 TU or 0.0002 mg./0.1 ml., 10 TU) ; ing. They include the tuberculin tine test, the and second strength (0.005 mg./0.1 ml., 250 Mantoux test, the Heaf test, and the injection TU) . gun test. The tuberculin tine test utilizes OT, The field of allergy and hypersensitivity is and the Mantoux, Heaf tests and injection concerned with an individuals abnormal reac- guns utilize PPD. tions to a specific substance with which he has had previous contact. Allergic reactions Mantoux test are divided into two main groups, immediate The Mantoux test is a procedure by which 0.1 (anaphylactic) and delayed (tuberculin type) . ml. of a test solution of PPD antigen is placed An example of an immediate reaction is intradermally in the skin of the suspect. The anaphylactic shock, which begins immediately strength of the test solution can be varied or within minutes after contact with the al- considerably to compensate for the type of lergen and disappears within hours. The prin- response anticipated. For persons in whom the cipal pathologic change consists of dilation chances of active tuberculosis are high, it is of capillaries and arterioles, with prominent advisable to use a dilute (first strength) test erythema and edema but little cellular infiltra- dose of 1 tuberculin unit (TU) of antigen con- tion. The reaction is associated with circulat- taining 0.00002 mg. of PPD per 0.1 ml. of solu- ing antibodies and can frequently be trans- tion. The hypersensitivity reaction to this dose ferred passively by means of serum. is rarely severe. For those in whom the risk of Examples of the delayed, or tuberculin type, tuberculosis is average, the intermediate reaction are bacterial allergy and tuberculin strength (called intermediate test dose) is the hypersensitivity. The reaction begins within antigen of choice. This contains 0.0001 or several hours or days after contact with the 0.0002 mg. of PPD per 0.1 ml. of test solution. allergen and lasts for several days. The main These two doses correspond to 5 TU and 10 pathologic reaction consists of inflammatory TU, respectively. For persons in whom the change, with predominant mononuclear infil- diagnosis of tuberculosis is suspected but hi 357/68 whom skin tests of lesser strength have been subject should be advised to return in from negative, the second strength antigen is avail- 48 to 72 hours, depending on the procedure able. This dose form contains 0.005 mg. of being followed by the testing team. The Man- PPD per 0.1 ml. of test solution. This dose toux test is best evaluated at 72 hours. Al- corresponds to 250 TU. The use of the second though erythema is frequently present, the strength testing antigen can produce severe size of the area of palpable induration is the necrotizing cutaneous reactions as well as cel- significant reaction to be observed. The test lular changes at the site of tuberculous lesions. site is carefully palpated, and if an area of The Mantoux test is suitable for screening induration is present, its limits are deter- programs or for use in private offices for mined and the transverse diameter is mea- single patients. sured, the largest diameter at right angles to It is important that exactly 0.1 ml. of test the long axis of the arm being noted. The in- antigen be injected and that the material be duration may be more or less easily recognized. placed intradermally as superficially as pos- It may vary from a firm, well-circumscribed sible, with the bevel of the needle facing up- density in the skin to a soft, ill-defined swelling. ward. It is best not to give the test dose in a The latter type may easily escape notice un- spot known to have been used for a previous less the site is palpated with a light touch. test. When the material is placed intradermal- An inexperienced observer may tend to over- ly, a small white wheal, from 6 to 10 mm. in estimate a strong reaction by failing to include diameter, will be raised. Its superficial surface its softer, flatter marginal part. Gentle strok- will resemble an orange peel. After a few ing of the area of induration will allow its out- minutes the wheal disappears, and the site of line to be appreciated. Marking the points at the needle puncture is the only sign that the which induration becomes noticeable to pal- test has been done. pation will facilitate measurement of the in- If the antigen is placed subcutaneously, a durated area. In recording the findings, the false negative response may be obtained. If size of the reaction in millimeters and the it is observed that the material is being de- strength of the test antigen used should be posited subcutaneously, the needle should be noted, rather than an impression or negative withdrawn and the material injected at a dif- or positive. The facts should be recorded, ferent site, which must be intradermal. If a as, for example, 7 mm. induration with 5 TU subject who would normally exhibit a positive at 72 hours. This type of information can be Mantoux reaction receives the test antigen sub- kept for evaluation in the future if the need cutaneously, he may experience mild systemic should arise.