BMJ Open 2:e001751 doi:10.1136/bmjopen-2012-001751
  • Infectious diseases
    • Research

Evaluation of the filter paper IP-10 tests in school children after exposure to tuberculosis: a prospective cohort study with a 4-year follow-up

  1. Morten Ruhwald5
  1. 1Department of Bacteriology and Immunology, Haartman Institute, University of Helsinki, Helsinki, Finland
  2. 2Laboratory of Clinical Microbiology, Eastern Finland Laboratory Centre Joint Authority Enterprise, Mikkeli, Finland
  3. 3Children's Hospital, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland
  4. 4Helsinki Municipal Epidemiology, Helsinki, Finland
  5. 5Clinical Research Centre, Copenhagen University Hospital, Hvidovre, Denmark
  1. Correspondence to Dr Morten Ruhwald; mruhwald{at}
  • Received 29 June 2012
  • Accepted 29 October 2012
  • Published 4 December 2012


Objectives The prevalence of active tuberculosis (TB) is low in Finland, but outbreaks do occur. Following exposure national guidelines recommend either tuberculosis skin test or interferon-γ-release assay-testing of asymptomatic children. The aim of this study was to compare QuantiFERON-TB Gold In-Tube test (QFT) and interferon-γ-inducible protein (IP-10) release assay for detection of Mycobacterium tuberculosis infection following exposure to TB in a primary school.

Design A prospective cohort study.

Setting School children in Helsinki, Finland.

Participants Two siblings of the index case and 58 classmates exposed to M tuberculosis.

Intervention All the children were screened using the QFT, which was used to guide preventive treatment. All those exposed were followed up through the national TB registry.

Outcome measures IP-10 was measured in plasma supernatants from the QFT test supernatants and in plasma dried and stored for 1 year on filter paper. IP-10 test results were calculated using preset algorithms for positive and indeterminate tests. The negative predictive values of the tests were assessed.

Results At an initial screening 2 months after the debut of symptoms in the index case, QFT was positive in two children; 56 tests were negative; one was indeterminate and one was borderline. IP-10 showed a perfect concordance between the dried plasma spot and plasma method; two children were IP-10 positive and two were IP-10 indeterminate. There were two (3%) discordant results between the QFT and IP-10 tests. Four children converted to positive QFT at a 1–3 month follow-up. None of the QFT negative/borderline children developed TB in the 4-year period since exposure.

Conclusions We demonstrated that IP-10 and QFT perform comparably as screening tools for infection with M tuberculosis in a contact investigation. IP-10 determined in dried plasma spots was at par with IP-10 determined in plasma, which further supports the usefulness of this alternative approach.

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