AFB Genexpert (Genexpert Test)

Afb Genexpert test (GeneXpert MTB/RIF)

It is a simple PCR test which is used to detect Mycobacterium tuberculosis (MTB) the causative organism of tuberculosis (TB). The other purpose of this test is to find whether the bacteria is responsive or unresponsive to a drug called rifampicin. It is a quick and accurate test which is useful in TB patients for early diagnosis and providing precise treatment.

Tuberculosis is a very common disease in India caused by a bacterium called Mycobacterium tuberculosis. It is a type of acid-fast bacilli (AFB). This disease is highly infectious (spreads from one person to another through tiny droplets) and predominantly affects the lungs. Tuberculosis is more common in people infected with HIV (human immunodeficiency virus).

The common symptoms of active pulmonary (lungs) TB are:

• Prolonged coughing for 3 weeks or more
• Blood in cough
• Chest pain, painful breathing, pain while coughing
• Unexplained Weight loss
• Fever with evening rise
• Loss of appetite
• Night sweats

The other less common sites which can be infected with tuberculosis are spine, brain, intestine, genitals, kidneys, joints, liver etc. Diagnosis of tuberculosis is done by the following methods:

• Tuberculin test
• Chest XRAY or CT scan
• Acid Fast staining (AFB staining) of the sample smear.
• Culture for MTB (can take 2-6 weeks) and antibiotic sensitivity testing (can take another 3 weeks) –to find the medications to which MTB is sensitive.

Tuberculosis treatment includes intake of many drugs which have to be taken for prolonged period. If not taken properly it may lead to development of drug resistant tuberculosis also called MDR TB. The common drugs used for treatment of tuberculosis are:

• Isoniazid
• Rifampicin
• Ethambutol
• Pyrazinamide
• Genexpert test detects MTB by identifying TB DNA in the sample. In addition to detection of MTB, it also identifies tuberculosis that is insensitive to rifampicin.

Advantages of Genexpert test:

• Quick result
• Reliable
• Cost effective

Why is Genexpert MTB test prescribed?

Your health care provider may prescribe this test for diagnosis of TB and to look for Rifampicin resistance in MTB. It is also useful for diagnosis of TB in those individuals whose microscopy report is negative for TB.

Samples which can be processed on Genexpert for detection of MTB

Various samples like Sputum, Pus, Tissue, CSF, body fluids, urine can be processed on Genexpert to detect MTB.

Procedure and prerequisites

This test is done with the help of disposable cartridge wherein sample from the person is mixed with reagent and cartridge containing this mixture is placed in the machine. It is a type of nucleic acid amplification/ PCR test. Its result should be interpreted with clinical, radiographic and other test findings.

Reference range

Result can be Mycobacterium tuberculosis detected or not detected.

If Mycobacterium tuberculosis is detected, resistance to rifampicin -detected, not detected or indeterminate will also be reported.