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Tuberculin reactivity in a chest clinic: the effects of age and prior BCG vaccination
Insights
Heaf tests in healthy individuals show that a strongly positive result is common in adults and does not necessarily indicate active tuberculosis infection. Local population data is crucial for interpreting tuberculin test results.
Area of Science:
- Immunology
- Infectious Diseases
- Public Health
Background:
- Tuberculosis (TB) diagnosis relies on tests like the Heaf test, but interpretation can be challenging.
- Understanding the prevalence of positive Heaf tests in a healthy population is essential for accurate TB diagnosis.
Purpose of the Study:
- To evaluate the significance of Heaf test results in a 'healthy' Caucasian population in Edinburgh.
- To determine the diagnostic value of strongly positive Heaf tests (grade III-IV) for active tuberculosis infection.
Main Methods:
- Heaf tests were conducted on 749 healthy adults and children from a tuberculosis contact clinic.
- Subjects were stratified by age, BCG vaccination status, and tuberculosis history.
- Results were analyzed to assess the correlation between Heaf test grades and demographic factors.
Main Results:
- In unvaccinated children, Heaf tests were predominantly negative or grade I. BCG-vaccinated children showed higher positive rates (grade I-II).
- Strongly positive Heaf tests (grade III-IV) increased with age in unvaccinated adults, peaking at 55% in the 45-65 age group.
- BCG-vaccinated adults had more low-grade positives (I-II) and fewer strong positives compared to unvaccinated adults.
Conclusions:
- A strongly positive Heaf test is frequent in healthy adults and has limited value for diagnosing active tuberculosis in the UK.
- Interpreting positive tuberculin tests requires considering the local population's tuberculin test profile.
Abstract:
Heaf tests were performed in 834 adults and children seen during one year in a tuberculosis contact clinic in Edinburgh. All subjects with a past history of tuberculosis, or who subsequently developed evidence of tuberculous infection and 63 subjects of Asian origin were excluded to leave 749 'healthy' adults and children broadly representative of the local caucasian population. All Heaf tests in 178 children without BCG vaccination were negative or grade I whereas 16 (73%) of the 22 children with a history of previous BCG vaccination were positive grade I or II. A strongly positive Heaf test (grade III-IV) in any child with or without previous BCG vaccination seen as a tuberculosis contact implies recent infection and merits consideration for chemoprophylaxis or prolonged follow-up. Two hundred and seventy adults without previous BCG vaccination showed an increasing incidence of strongly positive Heaf tests (grade III or IV) with age reaching a peak of 55% in the 45-65 age group; beyond the age of 65 this fell to 37%. Two hundred and eighty-one adults with previous BCG vaccination showed significantly more Heaf grades I and II, fewer negatives and fewer strong positives than the unvaccinated group. A strongly positive Heaf test (III-IV) is a frequent finding in a healthy adult and has little discriminatory value in the diagnosis of active tuberculosis infection in Edinburgh, and by implication elsewhere in the United Kingdom. Positive tuberculin tests should be viewed in the context of the tuberculin profile of the local population.