Case study scenario 1

1. Mum presents as group O RhD negative (rr) with immune anti-D detected, quantitation of 6 IU

2. At 32 weeks her anti-D level has risen sharply to 90 IU

3. In this time period no IUTs have been given

3. Baby delivered, severely anaemic, Bili increasing +++

4 Baby groups as O Rh D Negative, DAT strongly positive 5+IgG coating.

Questions:

1. Explain the above results

I am sure you'll all get it easily!.....may be someone else could post the next case:)

Rh typing on baby is not valid unless special technique was used to remove anti-D from baby's cell......

What we are seeing here is blocking phenomenon...where your RH result is false negative.

If baby's RH result is valid then mother has a antibody to a low frequency antigen!

How do you quantitate the anitbody?

I agree, blocking phenomenon....

I totally agree with Aakupaku,

Red blood cells with a positive DAT cann't be testing accuratly with blood typing reagents that require an indirect antigloulin technique unless they have been treated with CHLOROQUINE diphosphate to dissociate IgG from the red cell membrane.

An eluate prepared from the baby's cells should show anti-D, a very good inference that the corresponding antigen is on the cells.

How do you quantitate the anitbody?

I agree, blocking phenomenon....

Hi yolis76,

I have a PowerPoint lecture and accompanying Word Document that may help with your understanding of antibody quantitation. It's only 13 slides long, but I can't seem to upload it via the website.

I would be happy to send it to you if you supply me with your email address (either your own or your work).

If you would like to send it privately, my own email address is malcolm.needs@blueyonder.co.uk.

Yep ....far too easy for you guys!

The maternal anti-D antibodies had blocked the D antigen sites of the Rh D positive baby cells (as aakupaku said it's known as the 'blocking effect'). This prevented the anti-D reagent sera from reacting and agglutinating the D+ cells, resulting in a false Rh D - type.

I'll think of a harder one for next week !

I forgot to add that this effect is observable using IgM (rapid spin) anti-D antisera.