LPA Quality Assurance: Proficiency Testing

Steps Involved in Proficiency Testing (PT):

• Each new laboratory undertakes line probe assay (LPA) testing for 50 smear-positive TB affected patients​.
  • The specimen is anonymized (stripped of name and any personal identifiers), assigned a number, and processed by N-acetyl L-cysteine- Sodium Hydroxide (NALC-NaOH) method​.
  • Processed sputum deposit, DNA extracts and PCR products are stored at -20^oC​.
  • High resolution scanned images of the ‘line probe result form’ and the line probe assay result strips (scotch-taped onto separate LPA – run form) are sent to the Central TB Division/National Reference Laboratory (NRL).
• 20 DNA extracts are randomly selected by the NRL for testing concordance​.
  • The extracts are sent by express courier to the NRL​.
  • Blinded LPA testing on the 20 DNA extracts is done at NRL.​
• Once the pilot and proficiency phase has been satisfactorily completed, the LPA laboratory is assessed for proficiency, based on the following indicators: ​
  • The proportion of invalid LPA results; PT benchmark: less than 10%​
  • Contamination of negative controls; PT benchmark: Clean in all runs​
  • Internal concordance: concordance of results between 1^st and 2^nd tested parts for each specimen; PT benchmark: should be >95%​
  • External concordance: concordance of results of randomly selected specimens with the reference site; PT benchmark: should be >95%​.

Steps involved in Annual Proficiency Testing:

• Every NRL sends 30 cultures to the LPA laboratory.
• Cultures are taken for LPA procedures. DNA extraction is followed by: ​
  • Master mix preparation, amplification and hybridisation​.
  • The results are then shared with the respective NRL, who asses the results based on the following indicators: ​
    • ​The proportion of invalid LPA results; PT benchmark: less than 10%
    • Contamination of negative controls; PT benchmark: Clean in all runs​
    • External concordance; PT benchmark: should be >95%​.

Resources

• LPA Quality Assurance and Proficiency Assessment.

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