compatibility problem

[sona]

hey guys a big hello

i woud like to discuss a problem which i came across

i performed crossmatch by using gel cards of a particular " O POSIITIVE " bag which gave incompatible results with varoius patients samples

it was DAT negative can anyone tell me how to evaluate what the cause could be?

[rravkin@aol.com]

Sonya,

Did you try repeating the crossmatches using the tube method and LISS or PEG enhancement?

[Eagle Eye]

Did you crossmtach only that donor or other donor were crossmatched same time?

[Malcolm Needs ☆]

One reason could be that the red cells in the unit were expressing a low incidence antigen.

You would be amazed how many individuals have antibodies against a variety of low incidence antigen (without ever having any known stimulus, such as a transfusion or pregnancy).

That is only one possibility though.

I will put my "thinking cap" on.

Did you ABO type the unit again, just to make sure that it wasn't expressing a weak A or B antigen?

:eek:

[RR1]

Hi sona,

Can we assume that each patient you tested the unit against had a negative antibody screen by IAT ?

Also, are the screening cells produced in the same country where you are based and therefore similar to your patient population?

[sona]

thanks everybody

aakupaku we xm that particular donor with varoius patients

the patients antibody screen were negative using IAT and were compatible with other units and had no issues

ABO was also performed again gave clear o+ve group in forward and reverse

[Eagle Eye]

Do you wash donor cells before suspending them in MTS 2? (it's not required).

IF you don't, can you wash donor cells X3 and then make suspension in MTS 2 and repeat crossmatch?

Was DAT done in Gel? I have seen these kind of case where DAT is only positive by Gel and negative by tube method. But crossmatch was incompatible.

Your other crossmatches were compatible so most likely you ruled out false positive due to MTS diluent contamination. When you start seeing all incomaptible crossmatches for no obvious reason, you have to suspect your MTS diluent (crystal formation or bacterial contamination). In that case your negative QC would fail.

[Malcolm Needs ☆]

Do you wash donor cells before suspending them in MTS 2? (it's not required).

IF you don't, can you wash donor cells X3 and then make suspension in MTS 2 and repeat crossmatch?

Was DAT done in Gel? I have seen these kind of case where DAT is only positive by Gel and negative by tube method. But crossmatch was incompatible.

Your other crossmatches were compatible so most likely you ruled out false positive due to MTS diluent contamination. When you start seeing all incomaptible crossmatches for no obvious reason, you have to suspect your MTS diluent (crystal formation or bacterial contamination). In that case your negative QC would fail.

aakupaku makes some very good points.

If the DAT was performed in tubes, there is a chance that any weakly binding auto-antibody could have been washed off. This, of course, would not happen with gel.

:confused::confused:

[rravkin@aol.com]

In practice I have experienced numerous ocassions when the Gel cards showed reactivity and the tube method did not. There is a distinct sensitivity defference btween the two methods do to procedure and perhaps even more important the detection method. Where the donor DAT tube tests checked for microscopic agglutination? In this case you made need to. What were the reaction strengths of the incompatible crossmatches?

[sona]

In practice I have experienced numerous ocassions when the Gel cards showed reactivity and the tube method did not. There is a distinct sensitivity defference btween the two methods do to procedure and perhaps even more important the detection method. Where the donor DAT tube tests checked for microscopic agglutination? In this case you made need to. What were the reaction strengths of the incompatible crossmatches?

DAT was checked microscopically and the x matches showed incompatibilty from 1+ - 3+

as you said these two methods have sensitivity differences so do you prefer gel over tube as it is more sensitive .??

[rravkin@aol.com]

Sonya,

These reaction strengths are very significant. Did you retype the unit as Malcolm had suggested?

To answer your question on preference; I do not have a prefernce for either procedure. I untilize the procedures as needed. The primary procedure at my facility utilizes the Gel Method. If we get scratchy reaction(s) with the gel card and see the panel as negative we will sometimes repeat the Ab screen in tube just to see if the reaction holds up. Sometimes it does and but more times it doesn't.

Assuming that the DAT was perform using the Gel Cards I would suggest you check the card holders on the card centrifuge to make sure that they are in tact and are free of any obstruction. When the card spins the columns start out verticle, as you can see upon placing the card on the wheel, and then the columns are supposed to orient completely horizontal with centrifugal force. This force also causes the cells to migrate through the gel in the columb. If the card holder's movement is obstructed then card may not orient completely horizontal. When this happens the cells may not migrate to the bottom of the columb (if they are negeative of course) and the result may be what appears to be a positive reaction. While looking into this you may also want to repeat your AB Screens using freshly opened screening cells. This is a long shoot but I have seen that rarely the screening cells utilized with the gel over time sometimes do not give the same performance as when they were first opened for any number of reasons. The possibility that AB's were missed in three patients on the same day is unlikely but worth checking just the same especially since the DAT of the unit was negative. But check your card centrifuge first.

Also, a question for Malcolm; Malcolm do these reaction strengths of 1+ and 3+ correlate with the posiblity of a low incidence antigen as you had suggested? And if so can you give any insight on the probability that the cause is a low incidence antigen in comparison to the other potential causes for what we are seeing?

[Malcolm Needs ☆]

Sonya,

Also, a question for Malcolm; Malcolm do these reaction strengths of 1+ and 3+ correlate with the posiblity of a low incidence antigen as you had suggested? And if so can you give any insight on the probability that the cause is a low incidence antigen in comparison to the other potential causes for what we are seeing?

The honest answer is both yes and no.

It rather depends upon the antigen such an antibody could be directed against, and whether it is expressed equally on all red cells, such as the Wr(a) antigen of the Diego Blood Group System tends to be, or whether, like the P1 antigen for example, there is a marked difference in expression from one individual to another. A classic case of this variation in expression can be seen with antigens within the Knops Blood Group System.

The probability, as opposed to the possibility, is quite low, I will freely admit, but that having been said, there is evidence that many individuals seem to produce antibodies directed against a whole range of low incidence antigens, with little or no apparent stimulation (which actually suggests that the antibodies may be directed against an epitope that is carried by more than one antigen specificity).

If this donor does express a low incidence antigen (and it is a big if), then there is the possibility that the patients may all have produced an antibody against this "common" epitope, rather than an antigen specific epitope.

However, all that having been said, there are other explanations for this compatibility problem that have been put forward by other posters that are just as likely, if not more so.

:)

[sona]

thank you every body

[sona]

and please post if you find any info about this

[DAWNA1983]

Our reference lab recommends washing the segment cells.

[Yanxia]

Or the donor's T antigen exposure.

[Malcolm Needs ☆]

Or the donor's T antigen exposure.

Good point.

:)