Flow Cytometry Assay Speeds Diagnosis of Pediatric Tuberculosis

By LabMedica International staff writers
Posted on 15 Sep 2014

Epidemiologists working with samples obtained from groups of children in Tanzania, used a novel blood test to quickly diagnose victims of pediatric tuberculosis (TB).

The diagnosis of pediatric tuberculosis is complicated by nonspecific symptoms, difficult specimen collection, and the low number of organisms usually observed in biopsy specimens.

Image: M. tuberculosis (stained red) in tissue (blue) (Photo courtesy of Wikimedia Commons).

Investigators at the Swiss Tropical and Public Health Institute (Basel, Switzerland) and colleagues at Ludwigs-Maximilians-Universität (Munich, Germany) worked with samples collected from children with symptoms that suggested tuberculosis who had been prospectively recruited at the NIMR-Mbeya Medical Research Center in Mbeya (Tanzania), and the Ifakara Health Institute in Bagamoyo (Tanzania), between May 10, 2011, and September 4, 2012. Sputum and peripheral blood mononuclear cells were obtained for Mycobacterium tuberculosis culture and for performance assessment of the novel TAM-TB blood test.

The TAM-TB assay is based on flow cytometry detection of loss of the CD27 surface marker usually expressed on CD4+ T-cells. This marker disappears after infection of these cells by M. tuberculosis. Results from this assay are available in about 24 hours as compared to results from culture, which require about 20 days.

Among 290 children screened in this study, the investigators selected a subgroup of 130 to ensure testing of at least 20 with culture-confirmed tuberculosis. Of this group of 130, 17 children were excluded because of inconclusive TAM-TB assay results. The TAM-TB assay enabled detection of 15 of 18 culture-confirmed cases (sensitivity 83.3%). Specificity was 96.8% in the 63 cases that were classified as not tuberculosis, with little effect from latent tuberculosis infection. The TAM-TB assay identified five additional patients with highly probable or probable tuberculosis, in whom M. tuberculosis was not isolated.

"This rapid and reliable test has the great potential to significantly improve the diagnosis of active tuberculosis in children," said contributing author Dr. Klaus Reither, TB CHILD Program Manager at the Swiss Tropical and Public Health Institute.

The study was published in the September 1, 2014, online edition of the journal Lancet Infectious Diseases.

Related Links:
Swiss Tropical and Public Health Institute
Ludwigs-Maximilians-Universität