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LPA Quality Assurance: Proficiency Testing
Learning Objectives-
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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 -20oC.
- 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 1st and 2nd 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%.
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