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Gel Titer on Ortho Vision endpoint


Mabel Adams

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We are validating an Ortho Vision and considering whether to use it for doing gel titrations.  We have been doing tube titrations up to this point.  We ran one today on which the Vision recorded the result of the last positive dilution as 1+ but if we read the gel card manually we would call it W+ not 1+.  That would change the titer result.  The reaction the machine called 1+ appears significantly weaker than the photos in the Interpretation Guide showing various 1+ reactions (but strong enough to be called a true positive).  The instrument requires results review (not necessarily manual review of the card itself) of any positive reaction 1+ or weaker.  Is anyone else using the Vision for titrations?  Have you seen anything similar?  How would you determine the titer in such a a case?

Background information: This antibody is suspected to be RhIG but they had no record of a negative screen in this pregnancy.  We suspect that they plan to follow titers to make sure they are dropping.  The saline/IgG tube titer is 2 (in gentle, experienced hands-- but the 1:4 dilution tube was W+). The Vision gave a 16 if that well was called 1+ (8 if it was changed to negative--there is no choice for W+ on the analyzer). 

Edited by Mabel Adams
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We would like to start looking at this, but I didn't think it was FDA approved yet for titrations in the US.  Am I wrong Mabel?  We are just starting ABO titrations for incompatible heart transplants.  We are going to run in gel, and you are correct, that your cut off for gel will be 1+.  That being said, there is no weak+ defined for any gel reaction results (technically even if read by manual gel), so if we see any agglutination, we are calling it 1+ (and that would be our titer result).  Would love to hear back on how it goes for you. 

The note about requiring review if 1+ and lower; that is a setting that you can control on the Vision with your results cutoff on the analyzer, correct? 

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I do believe that we set the review threshold ourselves at 1+ and lower.  This means a human will look at it and struggle to call it 1+ when it is barely there.  If we do convince ourselves to call any visible reactivity in gel 1+ it means that the range of the the titer endpoints being called 1+ seems very broad--everything from 5 dots above the button to half way up the column.  If anyone else has done tube to Vision titer correlations I would be very interested in how much variation there is.  I know to expect gel to run 1-2 dilutions higher but the case above would be 3 dilutions higher--from 2 to 16.  Even if you have been doing manual gel titers I would like to hear if you have been calling any visible reactivity a 1+ and using that as your endpoint.

The Vision is approved in the US and IgG titers are included with that.  It can't do ABO titrations that I know of.

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Question. How likely are you to be doing titers on maternity patients that might have titers performed at another location? Since the sensitivity of Gel is higher than tube methods might you give the pt's caregiver confusing information if your titer is elevated due to method vs true rise in titer?

I only ask since this was a question in our region where there are multiple hospitals that do prenatal testing and sometimes patients/physicians don't stick to one lab. The consensus was that for prenatal titers the standard of care within the area hospitals is to perform the testing by the Uniform Tube method so that there weren't variations in titer strength based solely on methodology.

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4 hours ago, jalomahe said:

Question. How likely are you to be doing titers on maternity patients that might have titers performed at another location? Since the sensitivity of Gel is higher than tube methods might you give the pt's caregiver confusing information if your titer is elevated due to method vs true rise in titer?

I only ask since this was a question in our region where there are multiple hospitals that do prenatal testing and sometimes patients/physicians don't stick to one lab. The consensus was that for prenatal titers the standard of care within the area hospitals is to perform the testing by the Uniform Tube method so that there weren't variations in titer strength based solely on methodology.

I believe this is the main reason why we continue to do these types of titers by tube method. However, for isohemaglutinin titers (used for BMT or renal transplants, etc.) we use tube for IgM and gel for IgG. 

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We discontinued doing titers in gel last year because we kept failing the CAP surveys (our results were always too high). After research, I found this in the Technical Manual:

  • "The AABB-recommended method is the use of saline antihuman globulin (AHG) incubated for 60-minutes at 370 C. Other methods, such as using albumin AHG or gel, may result in higher titers than the recommended method and should be validated with clinical findings and laboratory data to ensure appropriate interpretation by the obstetrician and avoid inappropriate referral of patients for high-risk obstetric care."

We also retain the titered specimen and repeat it along with new titer requests to allow for possible operator differences.

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We are the only lab doing titrations for a 150 miles.  If we change to gel we will contact all of our OB/Gyns and the perinatologist that comes here periodically to explain our change plus put interpretive information in the report comments.  This is why I have never done them in gel before.  Doing them on the Vision would be convenient but all titrations on it are carried out to 10 dilutions (plus neat and a control) so it would have to be worth using up all of the reagent cells that it would require.  The variability of the endpoint plus the comments above about proficiency testing makes me hesitate even more.  I do see that gel titers are reported separately on the PT results now.  There is even a uniform method in gel. Ipregeno, were you submitting results under the gel uniform procedure and still getting too high?

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