Mantoux test revisited: Variability in reading tuberculin test in pediatric population
Keywords:interobserver variability, Mantoux test, tuberculin test, tuberculosis, PPD
Introduction: Mantoux test aids in the diagnosis of tuberculosis (TB), however its application and interpretation are dependent on multiple factors.
Methodology: A prospective study enrolling 400 children (aged 2-12) suspected to have tuberculosis. All participants received Mantoux test with two different strengths (1 TU and 5 TU) of Purified Protein Derivative (PPD) on different forearms. The test was read by two readers after 48 ± 2 and 72 ± 2 hours. Primary outcome was difference in the size of induration when read by two readers (interobserver variability). Secondary outcomes were difference in the size of induration at different intervals, with different strengths of PPD and percentage positivity of Mantoux test in TB patients.
Results: Statistically significant difference was seen in the size of induration when read by two different readers, with fair to moderate agreement when read at 48 and 72 hours (1 TU: p = 0.002, k = 0.52 and p = 0.1, k = 0.73 respectively, 5 TU: p = 0.001, k = 0.39 and p = 0.0009, k = 0.33 respectively). Tendency of under-reading occurred when size of induration was close to significant level (10-14 mm). Size of induration was similar when read at 48 or 72 hours (1 TU: p = 0.9, 5 TU: p = 1.0). Mantoux positivity rate in patients with TB was more with 5 TU as compared to 1 TU (61.2% vs. 16.3%).
Conclusions: There is significant interobserver variability with a tendency to under-read around the cutoff point. The use of 5 TU PPD at 48 hours by a trained physician can aid in early and more reliable diagnosis of TB.
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