This is the first report to demonstrate the validity of an instrument used in determining the need for a tuberculin skin test in children. The NYCDOH risk assessment strategy had a high sensitivity and negative predictive value in this cohort. Children with at least 1 identifiable risk factor were 35 times more likely to have a positive skin test result. Using this strategy, the vast majority of children in our sample would not have required a skin test, yet very few children with a positive skin test result would have been missed.
Most of the children not identified by the NYCDOH questionnaire but who later had a positive skin test result were older than 11 years. This may be because children in that age group, due to their increased mobility, are at higher risk of exposure to individuals outside of the immediate household. The NYCDOH questionnaire primarily focuses on household contacts. When we included this age group as a risk factor, the sensitivity of the questionnaire increased to 96.3% but the specificity dropped to 61.0%. In our sample, it would have meant testing an additional 723 children to pick up 3 positive skin test results. These circumstances may be acceptable to some clinicians. Obviously, the prevalence of reactive skin tests and TB in a given population should be considered in making such a decision.
Of note, 10 children with prior positive PPD results were excluded from this study. A retrospective review indicated that 9 of the 10 children would have been identified by the questionnaire. Therefore, the exclusion of children with prior positive tuberculin skin test results biased the results against the validity of the risk assessment questionnaire.
We did not make any attempts to verify the caretakers' answers to the risk assessment questions. It is possible that some of the responses may have been inaccurate. However, in the clinical setting, the truthfulness of these responses may not be as important as the caretakers' self-identification as belonging to a high-risk category. For the same reason, we accepted at face value a response of "no" to the questions. Additional information was obtained in some instances; for example, we inquired about the specific countries of travel.
The low positive predictive values calculated in this report reflect the prevalence rate (1%) of positive skin test results. In the clinical setting, however, the negative predictive values are more relevant for screening tests in which the vast majority of children do not have the disease. Positive predictive values are more critical with diagnostic tests such as the PPD. Universal PPD testing in low prevalence areas yields high false-positive results because of the direct relationship between positive predictive values and prevalence. The children in this study were drawn from a community with a high case rate of TB. Even in this setting, universal skin testing would have yielded high false-positive rates, based on our findings. While the screening questionnaire was validated in this setting, this approach should be examined in different settings with varying prevalence of TB.
This is the first report to demonstrate the validity of an instrument used in determining the need for a tuberculin skin test in children. The NYCDOH risk assessment strategy had a high sensitivity and negative predictive value in this cohort. Children with at least 1 identifiable risk factor were 35 times more likely to have a positive skin test result. Using this strategy, the vast majority of children in our sample would not have required a skin test, yet very few children with a positive skin test result would have been missed.Most of the children not identified by the NYCDOH questionnaire but who later had a positive skin test result were older than 11 years. This may be because children in that age group, due to their increased mobility, are at higher risk of exposure to individuals outside of the immediate household. The NYCDOH questionnaire primarily focuses on household contacts. When we included this age group as a risk factor, the sensitivity of the questionnaire increased to 96.3% but the specificity dropped to 61.0%. In our sample, it would have meant testing an additional 723 children to pick up 3 positive skin test results. These circumstances may be acceptable to some clinicians. Obviously, the prevalence of reactive skin tests and TB in a given population should be considered in making such a decision.Of note, 10 children with prior positive PPD results were excluded from this study. A retrospective review indicated that 9 of the 10 children would have been identified by the questionnaire. Therefore, the exclusion of children with prior positive tuberculin skin test results biased the results against the validity of the risk assessment questionnaire.We did not make any attempts to verify the caretakers' answers to the risk assessment questions. It is possible that some of the responses may have been inaccurate. However, in the clinical setting, the truthfulness of these responses may not be as important as the caretakers' self-identification as belonging to a high-risk category. For the same reason, we accepted at face value a response of "no" to the questions. Additional information was obtained in some instances; for example, we inquired about the specific countries of travel.The low positive predictive values calculated in this report reflect the prevalence rate (1%) of positive skin test results. In the clinical setting, however, the negative predictive values are more relevant for screening tests in which the vast majority of children do not have the disease. Positive predictive values are more critical with diagnostic tests such as the PPD. Universal PPD testing in low prevalence areas yields high false-positive results because of the direct relationship between positive predictive values and prevalence. The children in this study were drawn from a community with a high case rate of TB. Even in this setting, universal skin testing would have yielded high false-positive rates, based on our findings. While the screening questionnaire was validated in this setting, this approach should be examined in different settings with varying prevalence of TB.
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