DAT with IgG gel card

[frenchie]

Hi everybody!

We recently "failed" an API proficiency event for DATs:

Tube DAT AHG (POLY)=positive 1+

IgG gel DAT=positive 1+ (expected result was negative)

 So, here's what I did:

Repeated both DATs, results were the same. I washed the cells x3 and DAT gel was negative. I called API because 84 other labs reported the same positive result, and was told to contact the manufacturer because they believe there is an issue with the IgG gel cards. Before calling Ortho TS, I reviewed QC of reagents (MTS diluent, IgG cards) and MTS centrifuge and pipettes preventative maintenance, everything was satisfactory. I also reviewed the IFU, section Samples for DAT. TS informed me that the quality of the PT specimen is probably the cause...

Samples for Direct Antiglobulin Test (DAT)

• Samples intended for direct antiglobulin testing should be drawn into EDTA to prevent in vitro complement binding. If EDTA is unavailable, specimens drawn into ACD, CPD or CPDA-1 are preferable to non-anticoagulated clotted specimens. Red blood cells should be tested within 24 hours after collection. Clotted samples should not be refrigerated. Some samples such as cord blood, blood stored for extended periods of time, or blood that has been incompletely anticoagulated, may develop fibrin clots or particulates. The fibrin clots or particulates may interfere with the ID-MTS™ Gel Test and cause red blood cell entrapment at the top of the microtube. Testing should be repeated using red blood cells that have been washed to remove the clots or particulates.

• Red blood cells that are stored for extended periods of time may become coated in vitro with complement and globulin proteins. Those samples coated with IgG will then test as DAT positive with this reagent.

• Rouleaux caused by serum or plasma with abnormally high concentrations of protein (such as in patients with multiple myeloma or Waldenstrom’s macroglobulinemia or from patients who have received plasma expanders of high molecular weight) may infrequently cause difficulties in the ID-MTS™ Gel Test interpretation.9 False positive results or hazy reactions may occur with these samples but are rare. Samples exhibiting rouleaux should be washed several times in saline and retested.12 Laboratories are advised to consult their approved procedures.

• Hemolyzed and grossly icteric blood samples may cause difficulty in interpretation, and test results should be used with caution.

Now, I need to find the root cause and corrective action. I am thinking about a few options, one of them would be to wash all DAT positive in gel and supporting this with a validation/study.

But before, I would appreciate everyone's opinion and experience.

 

[David Saikin]

I have found that occasionally the IgG card will react to complement sensitized survey cells.  I think that CAP has finally realized this phenomenon and has samples produced that reduce the incidence of this.  I saw this first when I was lucky enough to have a research only DAT card that was used in Europe.  I had the same results, IgG and C both reactive.  I showed my boss and told her that we would take a hit on this because I knew that CAP was looking for only C reactivity.  We took the hit but I had pictures that I could send to defend my results. 

Have to remember that the folks making the survey may only have checked out their sample with tubes.  Also, many respondents tend to know what the survey is intended to detect and respond accordingly even though their serology differed.  Don't want to take a hit.

That's what I think

[galvania]

If 84 different labs saw the same thing then I can't see how it's down to you (and presumably the other 84 labs) to all independently look for the root cause.  If I were you, I would talk with the manufacturer, send them some of the sample and ask for their help.  Whatever they find will be valid for ALL of the labs, surely

anna