TB Risk Could Be Identified Using Blood Test
Millions of people around the world are at risk of developing active tuberculosis (TB), but until now, no test could identify these individuals. Now scientists have found a way to use a blood test to predict who will develop the disease.
Experts at Nationwide Children’s Hospital (NCH) conducted an international study in which they used gene expression microarray technology to analyze blood samples and develop blood profiles that are specific to infectious diseases such as TB, pneumonia, and bronchiolitis. This approach led the scientists to offer the first complete description of the blood transcriptional signature of TB.
TB Around the World and Identifying Risks
TB is caused by Mycobacterium tuberculosis, bacteria that typically attack the lungs. Approximately one-third of people around the world are infected with M. tuberculosis, but fortunately the infection remains dormant (latent) and asymptomatic in most individuals. People with latent TB have a 10 percent lifetime risk of developing active disease, although the challenge has been to identify who these people are before they develop symptoms.
According to the World Health Organization (WHO), there were an estimated 8.9 to 9.9 million incident cases of TB in 2008, 9.6 to 13.3 million prevalent cases, and 1.5 to 2.3 million deaths among both HIV-negative and HIV-positive individuals. A total of 12,898 cases were reported in the United States in 2008, according to the Centers for Disease Control and Prevention.
Octavio Ramilo, MD, and Asuncion Mejias, MD, investigators at the Center for Vaccines and Immunity in The Research Institute at NCH, were part of the international team that conducted the new study. The investigators examined and compared blood samples taken from patients in England and South Africa who had active, latent, or no TB. They then developed genome-wide transcriptional profiles for each of the study participants and discovered a distinct trait or “signature” in the blood from patients who had TB. These same patients had x-rays that also showed signs of active disease.
The study’s authors pointed out that 10 to 20 percent of patients with latent TB had signatures similar to those seen in patients with active disease. These findings “may identify those individuals who will develop disease, but longitudinal studies are needed to assess this,” according to Dr. Ramilo.
Dr. Mejias explained that the gene expression microarray technology they used “allows us to see the whole picture of infection using a single blood sample, which is a really powerful tool for the clinic.” In addition to identifying TB, Dr. Mejias noted that this blood test may also be helpful in the diagnosis and treatment of other infectious diseases.
Nationwide Children’s Hospital