Comparing the adrenaline-Pirquet test with international PPD tuberculin tests

Several tuberculins, strengths and setting methods are in everyday use. We wanted to compare the Norwegian reference adrenaline-Pirquet test with the internationally recommended Mantoux PPD test and Rhoditest. In responders of a random sample of young adults, with randomization of test subjects, we intra-individually compared the adrenaline-Pirquet (aP) test with Norwegian-produced synthetic medium tuberculin (SMT) with either the Mantoux test with PPD 2 tuberculin units (TU) (M2), the Mantoux-PPD 5 TU (M5) or the PPD 2 TU-Rhoditest (Rh). The criteria for a positive reaction were greater than or equal to 4 mm for the aP test, greater than or equal to 10 mm for the M2 test, greater than or equal to6 mm for the M5 test and greater than or equal to2 mm for the Rh test. Strongly positive reactions were defined as aP test greater than or equal to 10 mm and M2/M5 test greater than or equal to 15 mm. One of the tuberculin tests was positive while the comparison test was negative in 14% of the M2 test group (n = 236), 15% in the M5 test group (n = 162) and 20% in the Rh test group (n = 187). The three PPD tests had positive reactions 3-10 times as often, with a simultaneous negative aP test, than vice versa. Strongly positive reactions occurred in 7% of the aP tests (greater than or equal to 10 mm), 32% of the M2 tests (greater than or equal to 15 mm) and in 41% of the M5 tests (greater than or equal to 15 mm). Receiver operating characteristic (ROC) curves gave the best agreement, with aP test greater than or equal to3 mm compared with the M2 and the Rh tests. Regression equations are presented for transformations of the Norwegian reference method of adrenaline-Pirquet results to internationally recommended PPD tests. The international recommendations, globalization in general and the skill of Norwegian public health nurses in performing intra-dermal BCG suggest a future shift to the PPD 2 TU Mantoux test in Norway. Due to the lack of sensitivity and specificity of all tuberculin tests they might be used in targeted tuberculin testing and not as a general screening procedure in a low-incidence tuberculosis area with BCG-vaccinated inhabitants.