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Monday, May 6, 2013

Line Probe Assay - Rapid MDRTB Screening Assay

Line probe assays (LPAs) for tuberculosis were endorsed by the WHO in 2008 for molecular detection of drug resistance from smear-positive patients at risk of Multi Drug Resistant-Tuberculosis (MDRTB)
Two commercial LPAs are currently available:
  • INNO-LiPA Rif.TB test (Innogenetics NV, Gent, Belgium) and 
innogenetics line probe assay

GenoType MTBDRplus test (Hain Lifescience GmbH, Nehren, Germany).
line probe assay

Line Probe Assays for tuberculosis uses PCR/hybridization technique to identify members of the Mycobacterium Tuberculosis while simultaneously identifying drug-resistant strains by detecting the most common single nucleotide polymorphorisms (SNPs) associated with resistance. Meta-analyses have shown that LPAs are highly accurate for the detection of first-line drug resistance, especially in smear-positive sputum specimens.
WHO analysis of systematic reviews and meta-analyses showed that Line probe assays for tb are highly sensitive (≥97%) and specific (≥99%) for the detection of RIF resistance (Rifampicin resistance), alone or in combination with Isoniazid also known as isonicotinylhydrazine (INH) (sensitivity ≥90%; specificity ≥99%), on isolates of M. tuberculosis and on smear-positive sputum specimens.
Accuracy for detection of Multi Drug Resistant-TB was 99%, which remained unchanged when RIF resistance alone was used as a proxy marker for MDR-TB. Hain Lifesciences released the GenoType MTBDRsl test in 2009, designed to test for resistance to second-line anti-TB drugs (fluoroquinolones, ethambutol, aminoglycosides and cyclic peptides), and which can be used in combination with the MTBDRplus test to identify XDR-TB.

Advantages of Line Probe Assay for tuberculosis
  • It can be tested directly in smear-positive sputum samples.
  • It gives rapid drug susceptibility results without the need for culture.
  • LPAs can be used as the primary method for Drug Susceptibility Test on cultured isolates of M. tuberculosis, replacing phenotypic DST.
The major disadvantages of LPAs are
  • It is labour intensive
  • It require highly trained personnel and dedicated laboratory space and equipment.