TUBERCULOSIS (TB)

Introduction

TB is a disease caused by Mycobacterium tuberculosis. It is spread through the air from one person to another.WHO declared TB a global emergency. TB found to be directly responsible for 7% of all deaths and around 25% preventable deaths in the world. TB patients attributable to HIV infection.

TB Diagnosis

  • Based on physician's assessment of the patient's symptoms, such as persistent cough, fever and weight loss.
  • Combination of chest radiography and sputum examination for mycobacterium followed by sputum culture in suspected patient of pulmonary TB.
  • PCR (Polymerase chain reaction) assays, based on amplification of specific Mycobacterium tuberculosis TB DNA/RNA fragments isolated from samples
  • ELISA tests which detects IgG or IgG/IgM/IgA antibodies of Mycobacterium tuberculosis in patient.
  • Rapid tests which detects IgG / IgM / IgA antibodies of Mycobacterium tuberculosis in patient serum /plasma.

Limitations of all diagnostics procedure

  • Clinical & radiological sign of TB are notoriously non specific.
  • o In case of direct microscopic examination of acid fast bacilli, method is rapid but lacks sensitivity (ranging from 25 to 60%) and does not distinguish between different species of Mycobacterium.
  • Problems of collecting, of processing or interpreting sputum smears may also cause false negative results.
  • Culture techniques provide a definitive diagnosis but an expensive and time consuming techniques. Reliability vary from laboratory to laboratory.
  • New assay such as PCR are very promising but are expensive, lower sensitivity in extra pulmonary TB, their specificity for diagnosis active TB may be lower as a result of identification of non available mycobacterial DNA. Contamination of the sample may lead to false positive results.
  • Confirmatory information first can be obtained by performing a tuberculin (PPD) skin test. However only about 5% of person, Infected by mycobacterium tuberculosis develop clinically evident primary disease and a further 5% develop post primary disease, often after an interval at several years.
  • The large proportion of PPD reactions (Over 50%) may be due to cross reactivity with Mycobacterium other then tuberculosis.

An alternate method is required for screening the TB cases. The method of NANO TB test is rapid, inexpensive, safe & reliable for detection of antibodies against Mycobacterium tuberculosis.

Specimen for testing

The test can be performed on serum or plasma from TB patient, a body fluid which is rarely infected by M.TB. It also represents a safe, easy and reproducible alternative to the other diagnostic tests, which need carefully collected infected specimens.

NANO TB TEST

Qualitative test

  • Based upon immunochromatographic principle
  • The cocktail of five different recombinant antigen immobilized on nitrocellulose membrane (NCM) to capture the specific antibodies of Mycobacterium tuberculosis in TB disease cases.
  • In built control provided in test to validate the test procedure.
  • Detect the presence of IgG/IgM/IgA antibodies in TB patient which ensure the infection of mycobacterium tuberculosis.
  • Serum/plasma choice of specimen.
  • No dilution of sample required.
  • Visible result in form to pink/purple lines. Pink/purple line towards 'T` in addition to line towards 'C` indicates the presence of antibodies.
  • No instrumentation required to perform and read the result.
  • Results readable within 5-20 minutes
  • Simple procedure and clear interpretation.

Test procedure

  • Take TB test device and place on flat surface.
  • Add one drop of serum / plasma into sample well (S) using provided dropper.
  • Add 2-3 drops of Running Buffer, provided in the dropper bottle, into sample well(S).
  • Read result within 5-20 minutes after addition of the running buffer.

Interpretation of Results

Positive: Appearance of two pink/purple bands, one each in 'T' and 'C' region indicates that sample contains antibodies against MTB.

Negative: Appearance of only one colored band in the 'C' region indicates that the sample is negative for MTB antibodies.

Invalid: If there is no distinct pink/purple band visible in the 'C' region, the test is invalid and should be repeated.

COMPARISON OF DIAGNOSTIC TESTS FOR TB*

Assay. Sensitivity Specificity Time required
PPD skin test 65-70% 80% 2 days
Sputum smear 25-78% 99% 1 days
Sputum culture 82-87% 99% 2 weeks
Chest X-ray 80-85% 90% 2 hours
PCR 70-98% 70-98% 1 day
Elisa tests 62% 90% 90 minutes
Rapid test (Ameritek USA) Not Mentioned Not Mentioned 15 minutes
NANO TB 85%** 97%-99%** 5-20 minutes

*Sourced from available literature.

**In house data obtained from clinical TB positive and negative samples. Large-scale clinical trials under process.

 

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