Line Probe Assay [LPA]

Line Probe Assay (LPA) is a rapid molecular test available at centralised laboratories.

The assay is based on Polymerase Chain Reaction (PCR) that can simultaneously detect Mycobacterium tuberculosis complex as well as drug sensitivity to anti-TB drugs.

Figure 1: The GenoType MTBDRplus Molecular LPA Procedure; Source: Molecular Detection of Drug-resistant Tuberculosis by Line Probe Assay.

Advantages of LPA

• Rapid molecular test. (Turnaround time: 3-5 days)
• Highly sensitive and specific.
• Performed directly from sputum bacteriologically positive specimens and on isolates of M. tuberculosis complex grown from bacteriologically negative and bacteriologically positive specimens.
• Detects multiple gene mutations in anti-TB drugs.
  • First-line LPA detects mutations to rifampicin and isoniazid
  • Second-line LPA detects mutations to fluoroquinolones and aminoglycosides.
• Suitable for low and high-throughput labs.

Disadvantages of LPA

• Cannot be used as a point-of-care test.
• Requires appropriate laboratory infrastructure, equipment and biosafety precautions.
• Different rooms (DNA extraction, pre-amplification, amplification, post-amplification/ hybridization) are required to perform different steps (Figure 2).
• Requires trained manpower to perform tests and interpret test results.
• Stringent internal quality control is required to prevent contamination.

Figure 2: Amplification (A) and Post-amplification Laboratory (B) for LPA; Source: Molecular Detection of Drug-resistant Tuberculosis by Line Probe Assay.

Resources

• Guidelines for PMDT in India, 2021.
• Molecular Detection of Drug-resistant Tuberculosis by Line Probe Assay.

Assessment