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ksmith

QC for antibody titers

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Since an antibody titer is a semi-quantitative test, what is everyone doing for QC for this test? 

 

 

 

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Well, in the UK, the National External Quality Assurance Scheme (NEQAS) sends out titres on a regular basis, but, another way of doing this is to make a master titration of an antibody, aliquot it and freeze it, and then do an internal quality assessment using the frozen samples, or, better still, freeze the original sample and let individuals perform their own titrations and "mark" their efforts against the "mean score".

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As David said - we subscribe to the CAP survey for antibody titers. In addition, we freeze an aliquot to test in parallel with the next sample so that we can accurately identify titer increases vs techniques variations. We only perform antibody titers on pregnant women up until delivery.

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We have always participated in CAP Titer surveys and staff performs competency annually as well and haven't had any issues.  When we have a previous specimen, we perform the titer using the current & last specimen. 

In reviewing our testing for CAP's IQCP, our validated procedure is from the technical manual.  I was reviewing CFR493.1256 (d)(3)(iii) for this test system.  It states "Test procedures producing graded or tittered results, include a negative control material and a control material with graded or tittered reactivity respectively."  I was curious how others were meeting this CFR.

 

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How would you titer a negative?  Do the negative tubes at the end of the titer (when you exceed the titer) count as negatives?  

Did this refer to RPRs - sounds like the inspection requirements for RPRs - a graded positive set of controls and a negative control.  But even with RPRs, once you are titering, there is no true negative control (until you pass the point of patient reactivity).

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Just speculating here.............A specimen without an antibody would be expected to have a negative titer. Could you then use an antibody negative sample spiked with a specified amount of specificed antisera as a positive control, with the expectation of seeing a specific titer +/- 1 tube whenever tested, as your positive? Initially you would have to perform a titer on the 'positive control' multiple times in order to establish a range and/or maybe send it to a reference lab for a titer or titers. Once you have a titer established, you could run a specified range of dilutions that bracketed the end point for the positive control.

IQCP makes me glad that I decided to send titers out to our reference lab years ago :hooray:. Now I just have to decide if I'm going to part with some of our other special tests.

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