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TST, peripheral blood monocyte count helps identify risks for tuberculosis

The combination of tuberculin skin testing and peripheral blood monocyte count helped physicians identify people with Mycobacterium tuberculosis at risk for progression to tuberculosis, according to recently published data.

“This study reports … that an elevated peripheral blood monocyte rate combined with a strong [tuberculin] skin test response in the tuberculosis contacts were associated with a risk of progression to an active symptomatic tuberculosis disease,” Niaina Rakotosamimanana, PhD,  of the unit of mycobacteria at Pasteur Institute of Madagascar, told Healio.com/Pulmonology.

Niaina Rakotosamimanana

Rakotosamimanana and colleagues conducted a prospective longitudinal study to see if tuberculin skin testing (TST) combined with peripheral blood monocyte counts could identify people with latent-infected M. tuberculosis most at risk for developing active tuberculosis (TB).  

The analysis included 296 HIV-negative household contacts of patients with TB (n = 85) and 186 healthy controls.

Participants underwent monitoring of clinical features, full blood cell counts, TST and chest radiography performed routinely during 18 months of follow-up.

Researchers considered cutaneous induration of 5 mm or more in diameter to be a positive TST response and induration of 14 mm or more to be highly reactive.

Twelve household contacts developed symptoms consistent with active TB.

Eighty-three percent of those participants had a TST induration of 14 mm or more at enrollment, which indicated a significant risk for progression to active TB (aHR = 5.47; 95% CI, 1.18-25.33).

Elevated peripheral percentage of blood monocytes also indicated a significant appearance of TB disease symptoms (aOR = 6.25; 95% CI, 1.63-23.95).

Rakotosamimanana told Healio.com/Pulmonology the results of the study could improve methods of attempting to prevent the disease.

“The latently infected individuals — precisely the TB contacts — are at higher risk to develop an active TB disease,” he said.  “However, due to their huge number — one-third of humanity is estimated to be LTBI — it is impractical to provide any mass prophylactic treatment. The present findings could improve the existing strategies for TB preventive treatment by targeting the newly defined at risk individuals and could lead to substantial progress in global TB control efforts.” – by Ryan McDonald

Disclosure: The researchers report no relevant financial disclosures.