This page highlights some of the hot topics and current debates in TB diagnostics. Please use the discussion site if you would like to share your experiences or add to the debate.

What would be the ideal TB test? Click here for meeting report

HOT TOPIC I  NEW PCR TESTS. 

A new generation of molecular tests are arriving. Cepheid are leading the bunch with the launch of the Xpert MTB/RIF in Europe. It is the first 'plug and play' PCR test for TB.  It is a combination test for detecting pulmonary TB and resistance to rifampicin that uses real time PCR. Sputum is placed in a cassette which is loaded into the instrument. Sample prep and PCR takes about 2 hours to complete.  Data from the manufacturers and their co-developers looks very promising. Independent evaluation studies have  yet to be undertaken.

Roche are launching a real time PCR test. Their test was developed in South Africa and is designed to detect tuberculosis, avium or kansasii. It is based on their Light Cycler technology and does not include automated sample extraction.

HOT TOPIC II  Commercial culture systems

Commercial liquid culture systems are currently being promoted to assist diagnosis in resource poor TB endemic countries. 

What is the evidence that they will improve access to treatment?

What difference have they made to TB patients in places where they are already heavily used such as in South Africa?

Is the supply chain and technical backup adequate in all parts of the world or are we      buying into a 'white elephant' that will soon join the pile of unused technology scattered   across Africa?

Should we embrace the new technology and invest in new labs now, or wait for the molecular tests that might be safer/faster/cheaper?

Should we allow ourselves to become dependent on a monopoly or should we be also encouraging other commercial and/or non-commercial alternatives?

HOT TOPIC III   Line probe assays.

WHO recently endorsed the use of commercial tests for rapid detection of drug resistance. They are based on a PCR amplification of regions of genes where mutations can occur that cause resistance to rifampicin and isoniazid. A hybridisation (binding) step follows where the product of the PCR is allowed to bind to some specific DNA probes contained on a nylon strip, eventually resulting in the development of coloured bars (lines) on the membrane. The evidence suggests that when used properly the tests are quite accurate when detecting resistance to rifampicin in AFB positive sputum but less reliable for detecting INH resistance. 

The WHO endorsement was accompanied by a lot of positive press coverage.  WHO also issued a long document of recommendations that recognised the technical challenges and difficulties associated with the technology. This part of the document has so far attracted less attention.

What is the evidence that line probe assays have an impact on patient outcome in poor resource settings with weak health systems?

What is the evidence that line probe assays have an impact on patient outcomes in emerging economies or rich countries?

What is the 'turn around time' from the patent submitting a specimen to the clinician implementing a change in patient management?

Who should be tested and when should they be tested?

Will these tests change treatment or be used to lock people up?

Is the technology sustainable. The published studies were almost exclusively supervised by experts with post graduate training in molecular technologies, often on short term 'research funding'. Who will maintain the lab infrastructure, supervise the staff and run this service when the research project has ended? 

How much 'downtime' is there due to contamination?

What is an acceptable level of false positives?

Is knowledge of rifampicin resistance sufficient, or are other testing technologies needed that can assess susceptability to the other drugs?