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abillarn

Coombs Check acceptable reaction

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I need  any suggestion of  what is the acceptable reaction grading for Coombs Check cells.

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2+ is the only result possible as you have a mixed cell population in the tube now (patient/donor + check cells).

The definition of a 3+ and 4+ is a clear background = not mixed field.

And 1+ is just too weak, something is wrong.

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The reagent we use includes instructions that only specify a positive reaction is required.  It does not give a minimum grade. 

I remember being taught 2+ many years ago, but we now only require macroscopic agglutination.

sandra

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14 minutes ago, JPSCANNELL f. CROKE said:

2+ is the only result possible as you have a mixed cell population in the tube now (patient/donor + check cells).

The definition of a 3+ and 4+ is a clear background = not mixed field.

And 1+ is just too weak, something is wrong.

The avidity/reactivity of freshly-prepared antiglobulin control cells may be sufficiently high that the obligatory mixed-field result is not seen. The agglutination matrix of the sensitized cells often incorporates the un-sensitized test cells - a clear background is very possible.

Some workers believe that 2+ is too strong and that 1+ with antiglobulin control cells is the prefect result and allows detection of a decrease in sensitivity of the assay.

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If the check cells are agglutinated, then antiglobulin reagent was added to the tube, test confirmed.  There is no scientific evidence to support grading the reaction or to repeat the test if the strength of agglutination does not meet some arbitrary definition.

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25 minutes ago, Malcolm Needs said:

Grrrrrrrrrrrrrrrrrrrrrrr!!!!!!!!!!!!!!!!!!!

Anyone know the name of this man and his relevance to this thread?????

 

What's wrong Malcolm ? You don't like the idea of using a Coombs Test to find Kell- blood ??;)

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15 minutes ago, exlimey said:

What's wrong Malcolm ? You don't like the idea of using a Coombs Test to find Kell- blood ??;)

One of the only ways to detect Ko blood (apart from by molecular means - that still have to be proved serologically) is by use of the indirect antiglobulin technique (as you well know)!

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Thank you all for the responses and input.. The reagent manufacturer does not really specify what reaction grade is acceptable to validate your Coombs reagent really did its job. We were in the process of making our procedure , just not 100 percent sure what grade , we were leaning on 2+.

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41 minutes ago, abillarn said:

Thank you all for the responses and input.. The reagent manufacturer does not really specify what reaction grade is acceptable to validate your Coombs reagent really did its job. We were in the process of making our procedure , just not 100 percent sure what grade , we were leaning on 2+.

Do you plan to grade/record your antiglobulin control cell reactions ? If "YES", then you will need to define an acceptable range. Most workers simply use a check mark to signify satisfactory performance (hence "Check Cells"). In the absence of specific instructions and/or ranges from the antiglobulin control cell manufacturers, I favor the position suggested above by AuntiS: Macroscopic agglutination.

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I agree.  The check cells are not controls.  They do not need to have a specific "semi-quantitative" result--they just need to have a positive reaction to show that the wash step was adequate and that AHG was added. 

In your procedure you should just indicate that you get some arbitrary positive reaction:  1+, 2+/MF--whatever.  Just be sure you are not writing up something that disagrees with the manufacturer'e IFU.

Scott 

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When I first read the original question shortly after it was posted my immediate response was, "clumping".  I had missed the word grading.  I decided to wait to see what other responses would be.  I think why I missed the word grading is because we never graded the coombs control cells.  Either they clumped or they didn't.  Simple as that.  As noted above, all you are doing is confirming both that you added the AHG and it is working.  That's about as simple as anything we ever did.  :coffeecup:

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