Rule outs

[JAlvarez]

Hello all, I've been an observer for a while in this forum and I have found some usefull advise and insights to various isssues that also happens in my place. Now I have a quick question, just out of curiosity, How many Homozygous cells are used in your setting to rule out antibodies? One:) two or three:frown: . How about Kell? Is there any standard that addresses this?

Thanks

-JA

[Dawn]

There are two AABB standards that allude to ruling out, but there is nothing really specific.

BBTS Standard 5.13.3.1:

When clinically significant antibodies are detected, additional testing shall be performed.

IRL Standard 5.3.3 #1):

The laboratory shall exclude commonly encountered red cell alloantibodies.

AABB leaves it up to each facility to determine a specific policy for ruling out.

Our facility will rule out an antibody if three antigen positive cells fail to react, at least one of those must be homozygous, except:

• only one homozygous cell is required to rule out M, N, Lea, Leb
• only one antigen positive cell is required to rule out P1, this cell cannot have a weak expression of the antigen
• three heterozygous cells are acceptable for ruling out K
• when an Rh antibody has been identified, the other Rh antibodies can be ruled out using three heterozygous cells if needed

[Lcsmrz]

Alot depends on your comfort level and your patient population. A small rural site with one in-date panel will have a different set of rules than an AABB reference lab with three or four panels available, plus a frozen stock of rare cells and a rack full of antisera.

Clinical significance also plays a role in the small facility. In a patient with a well-defined Anti-E and no incompatible gel crossmatches with E-neg RBCs, I'm not going to spend alot of time and reagents trying to find an Anti-M reacting below room temp with only homozygous cells. I'm usually happy ruling-out with one homozygous or two heterozygous cells in gel -- apologies to Dr Judd for the use of common terminology.

The problem is dealing with reactions with no apparent specificity or with a patient with mutiple allo's. How far do you go before you write it off depends on being able to sleep at night ...

[Dawn]

I completely agree that it's okay for different labs to have different sets of rules for ruling in and out.

It is perfectly acceptable to use gel all the time and never even look at immediate spin. Immediate spin does nothing but get you into trouble. We are planning to drop it sometime in the near future.

Those junky workups that after 10 pages of work turn out to be nothing are absolutely awful. It is definitely hard to know where to draw the line.

In our lab we have lots of junky reactions in our gel screens. We used to take them to our reference lab and run a gel panel. Most junky gel screens turned into junky gel panels which propelled us into page after page of rule outs. Then finally we would go to PEG and everything would be clean. Not only were those workups a hassle to perform, but they were awful to review. Our solution was that all first time panels are done in PEG. If PEG is negative then we stop working it up. The overall quality of our patient care has improved due to increased turn around time for all workups. We have missed a few antibodies, but any method will miss antibodies. To be safe you would have to run PEG, LISS, gel, enzyme and DTT treated cell panels on every patient. And then you would still miss a few.

[Karen Olsen]

We have a combination rule of one homozygous if possible or two heterozygous if there are no homozygous available to rule out and then three positives and three negatives reacting appropriately. We never rule out Duffy's or Kidd's with heterozygous cells. We use gel to eliminate as much of the junky IS stuff as possible. It does still have some of it's own issues - but as stated above Peg usually resolves it.

[janet]

I

In our lab we have lots of junky reactions in our gel screens. We used to take them to our reference lab and run a gel panel. Most junky gel screens turned into junky gel panels which propelled us into page after page of rule outs. Then finally we would go to PEG and everything would be clean.

We also see 'junky' reactions in gel but we don't use PEG. If we can't get compatible units by gel we go to saline IAT testing. If there is no reaction that way we go with saline IAT crossmatched compatible units. If the saline IAT is reacting and we still can't figure it out off it goes to our reference lab.

[Mabel Adams]

We generally require one double-dose cell for rule-outs (from a homozygous donor--sorry, I know John Judd still lurks). For K, we accept 2 single-dose cells. For C and E in the presence of anti-D, we accept one single dose cell for rule out. The 3 pos and 3 neg rule applies to the statistical likelihood that a particular set of reactions could occur by chance rather than due to the presence of a specific antibody. By requiring 3 pos and 3 neg (or 2 pos and 5 neg) TO IDENTIFY AN ANTIBODY (not to rule one out) you are statistically pretty likely that the ID is accurate and not due to chance. These are the basic rules taught to our bench techs. More complicated cases, like multiples and antibodies to low-incidence antigens are handled by experienced staff on a case-by-case basis and occasionally some of the rules are not applied to the same degree.

Of course, Lewis can't actually have double dose cells, but they all look like they are double-dose on the panel, so it makes the rules appear consistent to the average generalist.

[jsherrie]

Roger that!