# 5703
Although following story was telegraphed earlier in the week by comments to the press by Mario Ravigli - the director of WHO's Stop TB Department – today we have the official announcement from the World Health Organization’s media centre, along with a detailed Policy Statement.
For the first time, the WHO has issued a “negative" policy recommendation against a well established practice used in Tuberculosis care.
The World Health organization is calling for countries to immediately ban the use of blood tests designed to detect active TB, and rely instead upon microbiological or molecular tests for the diagnosis of Tuberculosis.
The two main measures of the accuracy of a diagnostic test are sensitivity and specificity.
- Sensitivity is defined as the ability of a test to correctly identify individuals who have a given disease or condition.
- Specificity is defined as the ability of a test to exclude someone from having a disease or illness.
And based on a year-long review by the WHO and global experts – which examined 94 existing studies – researchers found overwhelming evidence that these serological diagnostic tests produced an `unacceptable level of wrong results’ (compared to WHO sanctioned tests).
They found both `low sensitivity’, where the test failed to identify TB in patients (which can lead to patients not receiving the appropriate treatment).
And `low specificity’, where the test indicated TB when the patient was not infected (which could lead to unwarranted treatment and no treatment for the true cause of their illness).
First, some excerpts from the WHO’s media centre press release, followed by a link to the Policy Statement, and the strongly worded conclusion from its executive summary.
WHO warns against the use of inaccurate blood tests for active tuberculosis
A substandard test with unreliable results
News release
20 July 2011 | GENEVA - The use of currently available commercial blood (serological) tests to diagnose active tuberculosis (TB) often leads to misdiagnosis, mistreatment and potential harm to public health, says WHO in a policy recommendation issued today. WHO is urging countries to ban the inaccurate and unapproved blood tests and instead rely on accurate microbiological or molecular tests, as recommended by WHO.
TB can be wrongly diagnosed
Testing for active TB disease through antibodies or antigens found in the blood is extremely difficult. Patients can have different antibody responses suggesting that they have active TB even when they do not. Antibodies may also develop against other organisms which again could wrongly indicate they have active TB. In addition, different organisms share the same antigens, making tests results unreliable. These factors can result in TB disease not being identified or wrongly diagnosed.
A blood test for diagnosing active TB disease is bad practice
"In the best interests of patients and caregivers in the private and public health sectors, WHO is calling for an end to the use of these serological tests to diagnose tuberculosis," said Dr Mario Raviglione, Director of WHO Stop TB Department. "A blood test for diagnosing active TB disease is bad practice. Test results are inconsistent, imprecise and put patients' lives in danger."
Today's policy recommendation applies to blood tests for active TB. Blood tests for inactive TB infection (also known as dormant or latent TB) are currently under review by WHO.
Commercial Serodiagnostic Tests for Diagnosis of Tuberculosis - Policy Statement pdf, 809kb
EXECUTIVE SUMMARY
Conclusions: Commercial serological tests provide inconsistent and imprecise findings resulting in highly variable values for sensitivity and specificity.
There is no evidence that existing commercial serological assays improve patient-important outcomes, and high proportions of false-positive and false-negative results adversely impact patient safety.
Overall data quality was graded as very low and it is strongly recommended that these tests not be used for the diagnosis of pulmonary and extra-pulmonary TB.
For some background on Tuberculosis, which kills 1.7 million people each year, last March I wrote a blog titled World TB Day: March 24th.
Some of the resources I cited that day may be of interest.
(From the 2011 TB Progress Report)
The World Health Organization released a new report and a factsheet on MDR-TB & XDR-TB in advance of this yearly event on the the status of Tuberculosis around the world and the progress being made in its control.
WHO progress report 2011
Towards universal access to diagnosis and treatment of MDR and XDR-TB by 2015
