Mantoux test revisited: Variability in reading tuberculin test in pediatric population
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Dimple Goel1, Mukta Mantan2, Gulshan R Sethi3
1Maulana Azad Medical College and associated Lok Nayak, Hospital, New Delhi, India. dr_dimplegoel@yahoo.co.in.
Insights
The Mantoux test for tuberculosis (TB) diagnosis shows significant interobserver variability, with a tendency to under-read results near the cutoff. Using 5 TU Purified Protein Derivative (PPD) at 48 hours improves diagnostic reliability.
Area of Science:
- Pediatrics
- Infectious Diseases
- Diagnostic Medicine
Background:
- The Mantoux test is crucial for tuberculosis (TB) diagnosis.
- Accurate interpretation of the Mantoux test is vital for effective TB management.
- Factors influencing Mantoux test application and interpretation require careful consideration.
Purpose of the Study:
- To evaluate interobserver variability in Mantoux test interpretation.
- To compare the efficacy of different Purified Protein Derivative (PPD) strengths (1 TU vs. 5 TU).
- To assess the impact of reading intervals (48 vs. 72 hours) on Mantoux test results.
Main Methods:
- A prospective study involved 400 children aged 2-12 suspected of having TB.
- Participants received Mantoux tests with 1 TU and 5 TU PPD on separate forearms.
- Induration sizes were measured by two readers at 48 ± 2 and 72 ± 2 hours.
Main Results:
- Significant interobserver variability was observed in induration size readings (p < 0.05).
- Agreement between readers was fair to moderate (Kappa values 0.33-0.73).
- The 5 TU PPD demonstrated a higher positivity rate (61.2%) in confirmed TB patients compared to 1 TU (16.3%).
Conclusions:
- Significant interobserver variability exists in Mantoux testing, with a tendency for under-reading near the diagnostic cutoff.
- The 5 TU PPD strength, when administered and read by a trained physician at 48 hours, may enhance the early and reliable diagnosis of TB.
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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