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exlimey

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Posts posted by exlimey

    This a classic case of Sensitivity vs Specificity. Clinical assays (including those in the transfusion medicine arena) are often designed to be as sensitive as possible, especially those intended to be frontline screens. Nobody wants to miss anything. However, the downside of this approach is that sometimes specificity suffers - more positives are obtained than desired.

    Solid Phase, Gel and PEG assays are super-sensitive, but may detect "nuisance" antibodies like weaker autoantibodies (warm and cold), or things like anti-P1, anti-Leb, or "HTLA-like" antibodies.

    Less sensitive assays that employ no enhancement (saline) or thing like LISS are sometimes used strategically to avoid the nuisances. Many institutions have policies that allow the deliberate down-regulation of sensitivity to ameliorate such problems. For example, performing crossmatches in LISS rather than Gel. Certainly, there's a risk that something might be missed using a less sensitive assay, but I think it's important to realize that in years past, the use of those less sensitive assays didn't leave a trail of bodies.

    In patients with long-term autoantibodies, it's not unusual for the autologous cells (DAT/autocontrol) to react weaker than Screening Cells or panel cells. The appears to be some kind of weakening of native antigens to which the autoantibody is directed. Sometimes, that may even mean the DAT is negative, but still yields a reactive eluate .

    You're concerned about "carry-over" ?  Probably the only reference to use of pipettes would be in the DFU from the manufacturer, but I suspect that they would not be that specific. Testing the "Last Wash" in parallel with the eluate is supposed to control the issue of adequate washing and/or carry-over.

    Our facility uses semiautomatic aspirators on which the stainless steel tip/needle is seldom changed, but sometimes flushed with tap water (if obviously bloody). Never had a problem.

    Is the "older tech" getting valid results ?

    On 6/24/2024 at 10:18 AM, Bet'naSBB said:

    maybe I didn't understand this statement.............I thought it implied that in doing "everything we can to avoid rouleaux/colds" from coming up was interpreted as us doing something deliberately to deviate from SOP???  :unsure::):D..........which we are not doing.........

    I think we're confusing ourselves. I was referring to the original post which suggested a modification of procedure in order to enhance rouleaux/colds.

    Serological assays are typically read "without undue delay", i.e., immediately. If some techs have a practice to "let tubes sit before looking at them", that could be construed as deviating from the procedure, unless they have some bizarre and very specific local instruction to do so.

    If the patient is being treated/transfused in a high level hospital with staff who understand Malcolm's explanation (above), then I would probably not recommend using O cells. However, I suspect that in many smaller hospitals it would be simpler from both administrative and technical understanding points of view to give O cells. This approach may not be ideal if the patient is a chronic or large volume user of red cells (those group O cells are a little more precious and useful in emergencies), and the laboratory now has to deal with an even bigger mixed field scenario.

    My experience with loss of ABO antigens is similar to Malcolm's description, but I never had the cool ability to track the patients' health.

    I echo the above sentiments - why go out of your way to "catch rouleaux and cold" which are just "a nuisance" ? It's a "waste [of] reagents and expensive technician's time."

    From a technical/regulatory point of view......if you do want to detect rouleaux and/or cold-reactive antibodies, use an assay/test designed to do so. I don't think the various regulatory bodies would appreciate what you're doing - a deliberate deviation from an existing test protocol or SOP.

    2 hours ago, Pamo said:

    Can anyone recommend a way to make up Elution Blinds aside from using previously analyzed specimens?

    First step is to determine what are you trying to prove. Do you want staff to merely have a productive/reactive eluate, or do you need them to identify the specificity, too?

    As Malcolm says, if you're in a blood center/centre, with access to whole units of plasma containing IgG antibodies of various specificities, it can be relatively easy to sensitize red cells with the appropriate phenotype (from your RBC inventory). Using D+ cells with anti-D is the simplest approach (or use Check Cells). This would certainly satisfy the mandate for a productive/reactive results. But, if you want the added challenge of antibody ID, using the same cocktail of reactants each time will lessen said challenge (as Cliff commented).

    But, back to basics.....make sure you have a specificity which is IgG in nature, reactive only by IAT. It should be relative strong WITHOUT LISS or PEG enhancement - use the standard/original saline-IAT to chose your antibody source. Always incubate your sensitization phase at 37C. You may need to vary the ratios of packed cells to serum to get optimal results (typically at least 2 volumes of antibody to one volume of packed cells). The shelf life of the sensitized cells may be increased by suspension in a red cell storage solution/preservative.

    I was taught, many, many moons ago, that prewarming should only be applied when the identity/specificity of the antibody is known/understood, i.e., you know what you're trying to avoid. Cold autos are probably the most commonly seen, but "nuisance" cold-reactive antibodies like anti-M, anti-P1, anti-Lea/Leb can also pop up and potentially be avoided using a prewarm version of an assay. These specificities are usually IgM class, are amenable to prewarming, and are generally considered clinically insignificant. Prewarming to "get around them" is often a good option.

    However, a cautionary note: There are cold-reactive antibodies that can present in a similar fashion that are clinically important - anti-Vel , anti-PP1Pk, for example. It can be dangerous to use prewarming to avoid these sometimes potent and potentially life-threatening alloantibodies.

    Prewarming may be a very useful tool, but as is true for very specialized tools, it should only be used and applied by trained and experienced operators who understand its strengths and weaknesses.

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