Jump to content

Recommended Posts

21 hours ago, diplomatic_scarf said:

IgG is only a monomer antibody and won't cause agglutination visible to the naked eye. 

Sorry, you must be fed up with me.  I know I am like a dog with a bone, but, although IgG is a monomer antibody, it does have a valency of two, which is why, occasionally, it can cause agglutination visible to the naked eye.  Notably, some examples of IgG anti-D cause agglutination at 37oC with D--/D-- red cells, with no potentiator.

Link to post
Share on other sites

Yes, you are completely right Malcolm and others.  My experience is limited to common positive DAT results for OB patients, which is the ABO mismatch. Those positives are usually 1+ or weaker. That's why we always do a microscopic if we get a macroscopic negative.  I forgot that Rh mismatch DATs can go from 2+ to 4+ positive, because I hardly ever come across those.  Thank you. 

Link to post
Share on other sites
  • 2 weeks later...

Read your circular of information for your specific antiglobulin reagents. Bio-Rad reagents are very specific. If no agglutination is observed macroscopically, it says, "Negative reactions may be examined with an agglutination viewer, however, microscopic examination is not recommended."


Link to post
Share on other sites

The original question was for all DATs, and this is from a reference lab perspective. We us Quotient for all three reagents. We use CAP. No we only VERY rarely use the scope, and it's at 10x rolling a tube and it's just for informational purposes. We also perform our DATs in Gel, with a significant difference between reaction strengths. Many times the tube is negative and the Gel is 1+ or 2+, so weak reactions should be caught there. Many identified Abs in eluates from tube negative, Gel 1+ samples. We HERE define optical aid to be a lighted mirror for tubes or laying the gel cards on an old school view box. (that doesn't mean it's the right way, just our way)  We have made an addition to our SOP to never use a mirror to read Gel cards. We allowed one tech to do this for almost a year and the amount of extra work was staggering with not a single clinically significant Ab identified. (that doesn't mean it's the right way, just our way) We don't use the scope because after many years of experience, (here) we determined that we were not viewing anything of clinical significance. I think that is the key, you have to balance risk/reward. If you use the "we have to do what's safest" theory, then you might end up running full panels and FICIN panels on negative screens. 

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Similar Content

    • By BloodbankZ
      I was wanting to get input on DAT's performed for Transfusion Reaction Investigations. Do you perform them with just IgG, C3d or both? TIA.
    • By SusieQ132
      Our facility is evaluating making a change to our process for Weak D testing for patients with a positive DAT.  For years, if we were required to do a Weak D, but the patient had a positive DAT, we used to cancel the Weak D as invalid.  Another hospital in our system mentioned that they tended to perform the Weak D, but then only cancel as invalid if the Weak D is positive.  We are thinking about changing to this process, as we now have to result many babies as "Rh Unknown" and give their mothers Rhogam.  
      Per our Anti-D's package insert:  "Red blood cells coated with alloantibodies or autoantibodies of the same or similar specificity as the reagent (i.e. cells that are DAT positive) may give weak reactions. This is due to decreased availability of antigen sites because of antigen blocking or steric hinderance. In extreme cases false-negative results may occur." 
      I'm worried about the "extreme cases" where a false negative could occur, but I cannot see this being common.  Also, would you think that if the cells were coated with that much antibody, that we would see any other odd reactivity in the ABO/Rh?  What do other facilities do?
      Thank you in advance,
    • By ejani
      I am sorry if this has been discussed previous... I searched and didn't find anything.  Quick question...
      We are transfusion service that performs DAT's using poly-clonal IgG... if it is positive, we run the mono-clonal IgG, however, we do not run the C3d.    How many of you would and/or do run the complement control cells for DAT QC in addition to Check Cells?  
    • By Jermin
      Hi All,
      I have a question, but firstly good old story time for some context. I came across a patient who had positive antibody screen on all three screening cells used (BioRad). I was concerned this may be an auto and pan-reactive, and required units. Performed a monospecific DAT, showing a positive reaction to IgG only. By this time antibody panel finished cooking and showed the patient may have anti-Fya , but couldn't do phenotype. By this time I was nearing my shift so handed it over to my colleague and asked for some units to be crossmatched. However, he refused as DAT was positive and said he rather send the sample to reference laboratory for them to crossmatch. The next day I crossmatched units to verify if it could have been done in our laboratory (just because I am sad that way), and turn out the unit I crossmatched was compatible (which I wasn't surprised about)
      Why does positive DAT (or the cause of positive DAT) sometimes interfere with IAT techniques (such as antibody panel and crossmatch) and sometimes it does not? If both use AHG, then wouldn't positive DAT with IgG cause antibody panels shows pan-reactive with red cells? But obviously it doesn't, but I'm trying to figure out why, and I'm sure the answer is quite obvious. 
      My laboratory seems very hesitant whenever they see anything regarding autoantibodies or positive DAT, and thinks that sample cannot be crossmatched in-house and needs to be sent off without even trying to investigate. Hopefully, by me asking this question, I can explain it back to my colleagues (but obviously take all the credit).
      Cheers in advance,
    • By Jermin
      Hi All,
      Its been a while since I came back to this forum, but glad I feel like I have gained a lot more insight. I feel like I'm a bottomless cup. 
      So I come with a question, for which there is not going to be a definitive answer (but with BB, is there ever one?), but hopefully, I would gain a bit of understanding.
      Background: So, our laboratory has started sending samples to reference laboratory for genotyping of the foetus by FDNA, which is great, since we would figure out the Rh(D) status of the baby (on most occasions) before they are born! So our laboratory has set up a flow chart which basically mentions that you do not need to send cord sample of Rh(D) negative mother if the baby is shown to be Rh(D) positive (or D positive, I am quite wary when trying to talk about Rh group), and only send cord if baby of Rh(D) negative mother if the FDNA shows the baby is Rh(D) negative, just to confirm the accuracy of FDNA. It sounds kinda counterintuitive, but we will soon be just not processing any cord sample for the ones we performed FDNA on. That means no cord Blood Group or DAT on a lot of post-delivery patients.
      Question:  By missing out DAT, we would possibly be missing out on detecting ABO incompatible HDN. How significant do you think it is in the early stages? Is it OK to wait to see if the patient shows signs of jaundice and for them to send a DCT sample afterwards? 
      Bonus Question: What does your Hospital/Laboratory do in the event of positive DAT on cord sample, and why do you do it?
      I had a read through one of the articles stating about the significant of DAT, but they called the Rh blood group as Rhesus, so I'm not going to take them too seriously

  • Advertisement

  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.