BioWorld International Correspondent

LONDON - A cheap, simple and accurate dipstick test for active tuberculosis could be available for use in the field within a few years, researchers predicted. The test would employ antibodies to detect combinations of proteins that have been shown to be present in the serum of people suffering from active tuberculosis, but not in healthy controls.

Sanjeev Krishna, professor of molecular parasitology and medicine at the Centre for Infection at St. George's Hospital at the University of London, said: "This work provides a fresh approach to an ancient problem. I think it is going to be very exciting to make this work in clinics where a test for tuberculosis is desperately needed. The next stage will be to use the biomarkers we have identified to develop a cheap, accurate and rapid diagnostic test that can be used easily and quickly out in the field."

The research - by Delmiro Fernandez-Reyes of the division of parasitology at the Medical Research Council's National Institute for Medical Research (NIMR) in London, with Dan Agranoff, also of St. George's Hospital, and Krishna and their colleagues - is published in Sept. 16, 2006, issue of The Lancet. The title of the paper is "Identification of diagnostic markers for tuberculosis by proteomic fingerprinting of serum."

The paper describes how the team has been able to identify a complex signature of biomarkers, such as proteins and enzymes, in the serum of people who have tuberculosis. They did that using a type of mass spectrometer called a SELDI (surface-enhanced laser desorption and ionization time-of-flight spectrometer).

Tuberculosis is the No. 1 cause of death by infection in the world, killing about 2 million people every year. Particularly in developing countries, it often is diagnosed by examination of sputum using a microscope, a method that is accurate in only 40 percent to 60 percent of cases. Culturing sputum for presence of Mycobacterium tuberculosis is a more reliable method of diagnosis but can take up to six weeks to give a result.

Clinicians throughout the world would therefore welcome a reliable test that could give immediate results, as this would mean being able to start treatment without delay.

Krishna, Fernandez-Reyes and their colleagues decided to find out if they could apply the concept of "proteomic fingerprinting" to assist in the development of new tests for tuberculosis. The idea is that certain diseases will cause unique and distinctive configurations of proteins to circulate in the blood.

The researchers compared the mass spectrometry "signature" of serum from 179 patients known to have tuberculosis with that of serum from 170 controls. Many of the controls had inflammatory conditions with clinical features that can overlap with those of tuberculosis.

Analysis of the complex patterns generated, coupled with statistical methods, allowed the team to identify a specific signature associated with tuberculosis infection. The use of the signature made it possible to distinguish between serum from people with tuberculosis and that from controls with 94 percent accuracy. The sensitivity of the test was 93.5 percent, and the specificity was 94.9 percent.

Further study made it possible to identify some of the proteins responsible for some parts of the signature.

Writing in The Lancet, the authors said: "Although SELDI technology can provide a diagnostic test for tuberculosis that makes no previous assumptions about the identities of proteins constituting an informative signature, cost and complexity preclude its general use. We therefore identified two of the 20 most discriminatory proteins to demonstrate the possibility of implementing more conventional diagnostic assays that are adaptable for field use."

The proteins, called serum amyloid A and transthyretin, already have been independently associated with the pathophysiology of tuberculosis, the authors add.

Fernandez-Reyes told BioWorld International: "Our work opens the door to further research into translating these findings to fast and reliable methods of detecting active tuberculosis infection that could have a major impact in global health. We currently apply similar approaches to malaria diagnosis. We are increasing the number of biomarkers selected from the signature to improve the accuracy of the rapid test."