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There could be overall weak or no signals on the strip, including or except, the Conjugate Control (CC) zone.

Figure: LPA showing No Signal Except CC 

Reasons and Troubleshooting for No Signal Except CC are given in the table below:

The limitations of Second Line Probe Assay (SL-LPA) are:

he examples of banding patterns for Second Line - Line Probe Assay (SL - LPA) are shown in the figure below.

Description

• All wild type bands display signal, mark as “+” against Wild Type (WT) column of the respective gene.
• If at least one of the wild type bands is absent, mark as “-“ against WT column. Similarly, “+” or “-” for Mutation probes (MUT).

Notes

• Bands with intensities similar or better than Amplification Control (AC) zone are considered.
• Not all bands of strip show same signal strength

Special Scenarios

Zone developed/ not developed (failing) in Wild Type (WT) and Mutation (MUT) probes are used to predict drugs resistance in First Line - Line Probe Assay (FL-LPA).

For Rifampicin

Table 1 shows mutations in rpoB gene and corresponding WT, MUT and responsible codons and mutations.

• rpoB WT1-8: rpoB wild type probes
• rpoB MUT1-3: rpoB mutation probes

Table 1: Mutations in the rpoB gene and corresponding wild type and mutation band; Source: GenoType MTBDR plus ver 2.0 kit, Instructions for Use.

Reporting Drug-resistance in Special Cases

First Line - Line Probe Assay (FL - LPA) can detect the mutations that are most frequently identified in resistant strains. 

However, there are certain limitations of the test as follows:

xamples of banding patterns for First Line - Line Probe Assay (FL - LPA) are shown in figure below.

Description

• All wild type bands display signal, mark as “+” against Wild Type (WT) column of the respective gene
• If at least one of the wild type bands is absent, mark as “-“ against WT column
• Similarly, “+” or “-” for Mutation (MUT) probes

Predicting Drug Resistance in Special Cases

Zone developed/ not developed (failed) in Wild Type (WT) and Mutation (MUT) probes are used to predict drugs resistance in Second Line - Line Probe Assay (SL - LPA).

For Fluoroquinolones (FLQ)

Tables 1 and 2 show mutations in gyrA, gyrB genes and corresponding WT, MUT and responsible codons and mutations:

• gyrA WT1-3: gyrA wild type probes; gyrA MUT1-2, 3A-3D: gyrA mutation probes
• gyrB WT: gyrB wild type probes; gyrB MUT1-2: gyrB mutation probes