DAT Mind Boggler!

[missyg]

DAT workup on a patient. At Hospital weak DAT positive (microscopic positive) IgG and Polyspecific post transfusion. We have performed the DAT in tube method and the complement and saline control were negative and check cell worked but the IgG and Polyspecific were negative (note we do Not read microscopiclly per Technical manual) but the IgG check cells failed on multiple attempts. We hand washed and used the automated cell washer and all check cells failed. Just out of curiosity, we used the complement check cells for the polyspecific and it worked. We do not have too much information on the patient. We have a few hypothesized reasons as to why the IgG seems to be neutralized but nothing concrete. Any suggestions?

[L106]

Did you repeat the Direct Antiglobulin Test and try additional washings before adding the Anti-IgG and Polyspecific Antihuman Globulin?

Sometimes we see this problem if the patient has a very high level of gammaglobulin in their plasma. (We also sometimes see that problem causing the patient's red blood cells to have a weakly positive Direct Antiglobulin Test.)

Donna

[Eagle Eye]

Did you QC your anti-IgG? Did it work? If you are not doing QC everyday...Here is the procedure..

1) Positive control: 1 drop of IgG coated check cells, wash X3, decant, add 2 drops of anti-IgG---should be positive

2) Negative control: 1 drop of screening cell(this is what we do), wash X3, decant, add 2 drops of anti-IgG---should be negative.

[missyg]

Yes we perform QC every day! It was also washed multiple times by different methods and it still does not check cell. Again it is only the IgG portion that is not working because we used the complement check cells with the polyspecific and it worked. Also to note that the DAT in gel was 3+ with Polyspecific and IgG cards but appears negative in tube (but not valid due to check cell failure)

[Liz]

What are you suspecting missyg?

[Malcolm Needs ☆]

It could be that the IgG was only bound weakly to the patient's red cells, and that the washing procedure (including the resuspension phase) could have allowed the antibody to dissociate. Gel does not have this washing procedure, of course, and so is much more sensitive in detecting low levels of weakly bound IgG.

When I say, it could be this, I am conjucturing about your particular case; the above about gel being more sensitive in decting bound IgG is a known fact.

[missyg]

Well we knew that something was happing to "neutralize" the IgG portion. We performed a mini cold and found a cold agglutinin present. We then decided to wash the cells with warm saline and it worked! We believe there was some kind of protein present that was neutralizing the IgG that was only removed by warm saline. But we have our result! Thank you to all who responded!