[Histonet] analytical specificity and interferring substances

[joelle weaver]

In dealing with this in SOPs I referred to the calculation methods outlined in the CLSI guidelines for technical procedures such the ones published for IHC/ISH & FISH , which helped me since most of the probes are at least ASR and I will potentially work with LDT's ( particularly with probes) . By my recollection the discussions in these guidelines provides examples of studies and formulas for calculation and determination of analytic sensitivity and specificity ( sorry don't have handy at the moment to provide a citation or page# and put this together more than 6 months ago), but I got my copies of the guidelines from the NSH site, and they are easy to find.  
 
My approach was to base the minimum case/slide requirements for pilot and trials for LDT's to more strict parameters than my ASR methods, and I just made worksheets to record results and for sign off similar to other types of validation, just more detailed. The most challenging part is quantifying/establishing measurements & values. For any IHC evaluation this applies to,  I used my usual qualitative scoring criteria (with an assigned quality score # for IHC) and carried this across IVD/ASR/LDT for consistency. When there is an ASCO or other score method, I incorporated those criteria.  The probes are easier  to define since the scoring is inherently more quantitative. I used the scoring criteria from the specification sheet for the most part for those. For doing the S & S trials, I had the initial calculations and documentation performed by the validating technologist, with review and final determination and calculation of analytic S & S- as well as the clinical application & utility to be made by the Medical Director. MD handles the report language. 
 
This was just my approach....I welcome critique and positive suggestions from the others.
 






Joelle Weaver MAOM, HTL (ASCP) QIHC
 
> Date: Tue, 8 Oct 2013 15:16:29 +0300
> From: shehnazster <@t> gmail.com
> To: histonet <@t> lists.utsouthwestern.edu
> Subject: [Histonet] analytical specificity and interferring substances
> 
> Hello Histonetters,
> 
> Could someone kindly shed some light on the follwing CAP standard and how
> to implement for histology and cytology:
> 
> *Analytical Specificity  /  Interferring Substances:*
> For modified FDA-cleared / approved tests or laboratory developed tests,
> the results of each validation study include a sufficient number of samples
> to establish the test's analytical specificity.
> NOTE: The analytic specificity refers to the ability of a test or procedure
> to correctly identify or quantify an entity in the presence of interferring
> or cross-reactive substances that might be expected to be present.
> 
> A million thanks
> 
> S. Kahn
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