Friday, May 13, 2011

Not all rejection is bad

In a recent proficiency testing sample for parasitology we submitted a sample with known artifact from poor handling (freezing).  I can’t say we sent this one totally on purpose, but we have in the past sent samples clearly designed and intended to challenge the laboratories’ rejection criteria.  What we observed was that less than 5% of the laboratories included a cautionary note about the quality of the sample.  
What I would have anticipated was that a substantial number of reports should have come back containing a cautionary note to the effect: “Caution: sample demonstrates artifacts suggestive of improper collection or handling.  Please submit an alternate sample”.

Proficiency Testing is supposed to challenge normal sample handling.  We hope that what we have seen is a failure of laboratories to handle this sample like a normal sample, rather than suggesting that  more than 95% of laboratories would generate a report without commenting on suboptimal quality of the sample.   

Laboratories know all too well that a number of samples reach the laboratory in an unacceptable condition.  They may have been collected incorrectly, or perhaps put into the wrong container with the wrong fixative or anti-coagulant.  They may have been collected properly, but not labeled in a way that anyone could say with any confidence from which patient they came.  Or they may have been collected properly, and labeled properly, but transported in a way that would not protect the sample from complete or near complete decay.  Unfortunately for all those reasons, the samples all fall into the same category: junk samples.

Working on junk samples is not only counter productive, it is dangerous because  reports virtually never include the cautionary statement “please note that this result has little chance of being accurate or relevant due to the poor quality of the sample.”  

ISO15189:2007 includes the requirement for sample Rejection Criteria (see requirement 5.4.8).  Laboratories have an obligation to establish the requirements of a sample, and to reject samples that don’t meet the requirements.  It is for the good of the patient, and for the good of the clinician to avoid making decisions based upon faulty information from faulty specimens.  

And we believe that PT programs have an obligation to intermittently challenge the laboratories’ decision making.  Is there any difference between demonstrating that a laboratory tested a good sample and got a wrong answer or demonstrating that a laboratory tested a poor sample and got a poor answer?  Well there is a difference, but the bottom line is the same.  The clinician receives a report with information potentially damaging to patient care.

At this point, let me point out that even the international standard misses an important consideration of sample rejection.  Not all sample rejection is the same.  There are different levels of rejection, all of which are acceptable, appropriate and to be expected in their respective situations.  And proficiency testing schemes are ideally placed to challenge all these level.

More on this later.

PS: For those that want or need more information on the international standard, see: The ISO 15189:essentials - A practical handbook for implementing the ISO15189:2007 standard for medical laboratories.  November 2010.  CSA Standards.
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