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Investigating PT Failure
A systematic approach to PT failure investigation is required and easily adaptable to all laboratory environments. Several causes for PT failure are discussed below. Each cause should be thoroughly examined. Additionally, laboratories should document completely each step of investigation taken in their effort to uncover the source of failure.
Before returning the booklet to AAFP-PT, make a photocopy of the form. This serves an important purpose because it provides documentation of the lab’s results.
If the data was entered incorrectly by AAFP-PT, it can be corrected. AAFP-PT must be notified of the need for a correction within four weeks of receipt of the Evaluation Report.
When investigating PT failure for a qualitative analyte, testing procedure error should be reviewed. Some qualitative tests contain internal controls that will indicate when an error in procedure has occurred while others do not. It is important to identify any possible source of procedure error before dismissing a quality control problem.
Peer Group Evaluation
If there are not enough laboratories using the same instrumentation or kit to form a peer group, alternative grading criteria may be applied. This type of evaluation can occasionally result in PT failure. AAFP-PT can be of assistance in determining whether the laboratory was at fault or whether the failure was due to the evaluation method.
Occasionally, an instrument or method may display a matrix effect with the PT specimens. This occurs when a positive or negative bias is noted with PT specimen testing but there is no actual bias when testing patients. This is most likely due to a constituent or artifact in the manufactured specimen. Matrix effects should be investigated and your instrument manufacturer and AAFP-PT should be notified when suspected.
- Check instrument maintenance log to see if the instrument was due for maintenance or if a problem occurred shortly after PT was performed. Check reagent expiration dates and lot numbers. Determine if the reagent was close to expiration or if a new lot number was recently opened.
- Check the calibration record. Check to see if calibrations were done on schedule or if calibration was due.
- Contact the instrument/reagent manufacturer to identify any possible matrix effect problems.
- Specimen dilution error may have occurred.
- Check instrument linearity ranges. Results reported outside linearity limits are not reliable and should not be reported until the dilution protocol confirms the result. If normal laboratory procedure does not include a dilution protocol, contact AAFP-PT for specific documentation procedures.
- Review laboratory records and specimen results for possible result transposition or specimen mix-up.
Only after all possible avenues have been fully investigated can the assumption of random error be ascertained. Statistics indicate that one out of every 20 results will fall outside its specified limit. This should be documented as random error or normal statistical variation.
This type of error is one that occurs in a procedure but is not innate to the procedure itself. Statistical outliers can result from random error. It is important to fully employ all sources of assistance when investigating instances of PT failure. AAFP-PT, instrument/kit manufacturers and reagent/supply vendors are important resources for the laboratory. Complete documentation is required by CLIA 88.