Ultrasonography – a novel auxiliary interpretive approach for tuberculin-purified pure protein derivative skin test: a comparative study

BACKGROUND: The tuberculin-purified protein derivative (PPD) test is commonly used as a screening tool for tuberculosis (TB). However, the traditional judgment standard of the PPD test is influenced by subjective factors, which can lead to less accurate and intuitive test results. OBJECTIVES: To evaluate the accuracy of ultrasonography as a novel auxiliary judgment method for the tuberculin-PPD test and its clinical application. DESIGN: This study was designed as a comparative study following the STROBE guidance. METHODS: From February to May 2022, 208 patients with active tuberculosis infection were enrolled. Manual judgment and ultrasonography were employed in a double-blind-utilized manner, and the PPD examination results were recorded. Kappa statistic was performed to measure the concordance between the two diagnostic methods. Fisher’s exact test was used for the analyses of the PPD test results of all 208 active tuberculosis infection patients’ PPD results. RESULTS: There was a significant difference between the two methods in the PPD result judgment (p < 0.001), particularly in the positive ratio of the PPD test results, (p < 0.05). Overall, 50 patients were determined as PPD positive based on manual judgment. However, only 24 patients’ PPD test results were determined as positive via ultrasonography. The remaining 26 patients should have been classified as strong positive but were misclassified as positive. The misdiagnosis ratio was 52% (26/50). CONCLUSION: Ultrasonography has superior accuracy to traditional manual judgment. Moreover, it does not rely on sophisticated clinical experience or training and can reveal subtle changes of the skin corresponding to each PPD test result providing intuitive results. In conclusion, ultrasonography can be used as an auxiliary interpretive approach for PPD test and has a promising future for clinical application.