One of the most dreaded events in the laboratory is when the result of a proficiency test challenge comes back with "Failed" or "Out of Compliance" comment. Now what? You need to troubleshoot it, and that does not mean you run it again and if it comes within acceptable limits and then you are done- that is not troubleshooting- it is a part of it. So where do you start, controls, curve, QC, technologist competency, reagents? All again a part of troubleshooting, but in the words of Julie Andrews, "Let's start at the very beginning" (in case you don't know who she is, think Sound of Music).
Quality of testing in the laboratory can be defined as the "degree to which the laboratories' data provide valuable support to the clinical decision making and are developed in accordance with the best laboratory practices."(1) Proficiency testing (PT) is a tool used by laboratories quality assurance (QA) programs to assess analytical variability as well as to evaluate precision and accuracy of testing. It also can aid in identifying areas for improvement as well as initiating a corrective action.(2) PT has helped laboratories to accurately measure, monitor and improve analytical performance over time.(1) For all tests that are performed in the Coagulation laboratory a mechanism must be in place to ensure that laboratories are in compliance with their peers. PT or external quality assessment is a part of every laboratories tool box to aid in this task(3). Most special coagulation tests are not regulated however they must be tested twice/year. If a PT is not available for a certain test such as an esoteric test, non-viable material, or a new test, the PT must be performed using an alternative assessment such as split sample or sent to a reference laboratory. It is important that limits of acceptability be defined and adhered to for testing.
The major benefits of proficiency testing are to:
- Enhance patient care and safety through improved laboratory testing.
- Characterize test accuracy and precision across multiple methods.
- Correlate specific method variables with accuracy and precision.
- Identify interfering substances and quantify their effects across multiple methods.
- Identify clinical laboratories that are at risk for poor performance so that their performance can improve.
- Satisfy accreditation and regulatory requirements.
It is strongly advisable when you are running a PT sample to keep a copy of the QC for that day, a copy of any calibration curve, as well as putting aside a sample or two that were run with the PT, if you don't freeze and store samples that can easily be retrieved. This way if you need to troubleshoot, you have everything you need without hunting for all this information.
Handling an out of compliance result:
So where do you begin? First look at the results from the proficiency report. Look at how your instrument/reagent peer group performs. That is a huge amount of information. Let's say if your result is higher than the acceptable limit, does your peer group run higher than the rest of the peer groups? How far are you out? What is your laboratories CV for a result at this level? All of this will help you gauge if it is just a random error or do you have a systemic error? Next let's look at your QC, how is it running, are you within range, but you are running on the upper limit, a positive bias? What about your calibration curve? Does it match previous standard curves, or is it difference, and does the difference fall with the range of the result that was out of compliance? Also check the level of your calibrator, has it been assigned the correct value? All of this should be done before re-running the PT sample. It is also important to look at the testing that was performed on the day of the testing for the PT, what about those patients? They also need to be rerun? You may have a statistically significant result when they are rerun, but not a clinically significant result. Of course, all of this hinges on that you have enough PT sample left so you can rerun- what if you don't? How do you troubleshoot this? As a last ditch effort, try looking for a sample that is within the acceptable range of the PT to rerun. The last thing to look at is, who ran the test, when was the last time they were assessed for competency? Have they failed a PT challenge before? Each technologist puts their own spin on procedures and they can cause a result to spin out of control.
Example for an abnormal PT challenge:
The acceptable result was 100- 150%, your laboratory reported 156%, so you are above acceptable limits. A review of the peer group for your instrument/reagent combination has a mean value of 142%, while other peer groups look to be at 123%, and 119%, so your testing is running at a higher mean, which may also translate to your laboratory having a higher mean for your reference interval. Next look at your quality control. The upper limit for your normal control is 125% and pathological control is 45%, and results that day were 122% and 43%, while they were within limits they fell on the high side. A review of the calibration curve did not demonstrate any differences from the previous calibration curve, however when the dilutions for the factor assays were reviewed the results varied: the 1:10 150%, 1:20 158% and the 1:40 162% with an average of 156%. Results are higher, as are the controls on the high range, as well as the peer group having a higher mean- all contribute to this result. When you repeat the sample, it comes in at 148% so it is within acceptable limits, however it is on the high side. That day two patients were tested for Factor IX, one had a result of 67% with a rerun value of 70% and another with a value of 172% which repeated at 166%. The laboratory reference range for FIX is 60-160%, so both results do not change the outcome of the FIX, upon the repeat the normal is still normal, and the high is still elevated.
If the result was on the boarder of a reference interval and the sample went from a normal result to an abnormal result, you might want to look at a precision study at that level to determine if your CV's are too wide, this may require a service call and further investigation.
So, your answer is a combination of things, a higher peer group, an answer just above the acceptable limits and QC running on the high side. This should be watched to see if you are seeing a trend or it was just a random day with high controls, maybe pointing to the reagent reconstitution.
It is important that laboratories perform adequate corrective action when troubleshooting a PT result. This may lead to a better quality of testing, reliable test results and of course ensure patient safety. Just rerunning a sample doesn’t help your laboratory get to the root of the problem and if not investigated properly can impact patient testing.
- Lippi, G., Plebani, M. The use of quality indicators for the pre-analytical phase, Quality in the Medical Laboratory, ECAT Foundation, Special Issue 6, pg 8-9, 2016.
- Adcock, D., VW testing: Performance of results of QA studies, Mayo/Nascola Conference, MN, 4/26/2007.
- College of American Pathology Checklist, Laboratory General, PT, CAP Inspection directive HEM 20035.