Molecular Test Detects Active Tuberculosis in HIV Patients

A major impediment to tuberculosis control in Africa is the difficulty in diagnosing active tuberculosis (TB), particularly in the context of human immunodeficiency virus (HIV) infections.

A set of RNA transcriptional signatures expressed in the blood of patients might provide the basis of a diagnostic test that can distinguish active TB from latent TB (LTBI), including from other diseases that have similar clinical symptoms and signs.

An international team of scientists led by those at Imperial College London (UK) recruited 584 adult patients with suspected TB in South Africa and Malawi who were eventually diagnosed with either TB, latent TB infection or another disease, where TB was considered in the differential diagnosis, but then excluded. They took blood samples from these patients and analyzed their blood transcriptional profiles to identify signatures that could be used to calculate a disease risk score capable of differentiating TB from other conditions prevalent in HIV-infected and -uninfected African adults.

The whole blood that was collected before or within 24 hours of commencing TB treatment in suspected patients at the time of recruitment, in PAXgene blood ribonucleic acid (RNA) tubes (PreAnalytiX; Hombrechtikon, Switzerland), frozen within three hours of collection, and later extracted using PAXgene blood RNA kits. RNA was shipped frozen to Singapore for analysis on HumanHT-12 v.4 expression Beadarrays (Illumina; San Diego, CA).

A 27-transcript signature distinguished TB from LTBI and a 44-transcript signature distinguished TB from other diseases. To evaluate the signatures, they used a novel computational method to calculate a disease risk score (DRS) for each patient. The classification based on this score was first evaluated in the test cohort, and then validated in an independent publically available dataset. In the independent validation cohort, the investigators found that patients with TB could be distinguished from patients with latent TB, with a sensitivity of 95% and a specificity of 94%, and from patients with other diseases where the sensitivity was 100% and specificity was 96%.

The authors concludes that from a clinical perspective a simple transcriptome-based test that reliably diagnoses or excludes TB in the majority of patients undergoing investigation for suspected TB. The use of a single blood sample would be of great value, allowing scarce hospital resources to be focused on the small proportion of patients where the result was indeterminate. The challenge is to develop innovative methods to translate multitranscript signatures into simple, cheap tests for TB suitable for use in African health facilities. The study was published on October 22, 2013, in the journal Public Library of Science Medicine.

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Imperial College London
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