Principle:

Immediate-spin crossmatch ISXM is an abbreviated compatibility testing that detects most ABO incompatibility.  AABB Standards restricts its use to specific situations as indicated in the Policy section below.

Policy:

1. Applicability:
   1. ISXM may only be used when ALL of the following conditions are met:
      1. Negative antibody screen
      1. No history of antibodies
      1. No ABO/D antigen typing discrepancies
      1. Less than two (2) ABO/D determinations are on-file.
   2. Use the computer/electronic crossmatch whenever its specific criteria are met.
2. Testing:
   1. ISXM consists of reacting an RBC suspension with patient/serum or plasma, centrifuging, and immediately reading for agglutination or hemolysis.  THERE IS NO INCUBATION STEP, NO USE OF ANTIHUMAN GLOBULIN AHG REAGENT.
   2. If any hemolysis or agglutination is detected, the crossmatch is incompatible:
      1. Repeat the ISXM.
      2. Repeat the patient ABO/D AND unit ABO/D typings.
      3. Repeat the antibody screen.
      4. Perform full AHG crossmatch AND AHG/enzyme antibody panels.
      5. Refer the case to senior technical staff or a Transfusion Medicine consultant for further instructions.
         1. Case review will be documented in Medinfo HIIG computer system.
      6. DO NOT RELEASE THE RBCS UNTIL SO INSTRUCTED BY SENIOR STAFF.

References:

1. Technical Manual, Current Edition, AABB, Bethesda, MD, USA
2. Standards for Blood Banks and Transfusion Services, Current Edition, AABB, Bethesda, MD, USA
3. Guidelines to the Preparation, Use, and Quality Assurance of Blood Components, European Committee (Partial Agreement) on Blood Transfusion (CD-P-TS), Current Edition

The antiglobulin phase crossmatch is the same indirect antiglobulin test IAT used for antibody screening, only instead of reagent RBCs we use the donor’s RBCs.  One question I like to ask my students is to describe the difference between the IAT and the antibody screen.  Most don’t realize they are the same thing, the same procedure, i.e. mixing plasma/serum with RBCs and then detecting a reaction using the AHG reagen

In Medinfo, the AHG phase crossmatch will be required unless the criteria for electronic crossmatch have been met (see my previous post on this topic).  In emergency mode, one can also do a class II release using immediate-spin to detect ABO incompatibility.  Medinfo will check the historical records for previous antibodies.

Notice that the process includes contingencies for room and even lower temperature conditions as well as immediate-spin.

I warn my students that we can make any tube, gel or glass-bead well react if we do not strictly adhere to the manufacturer’s recommendations.  The simplest example is to leave the reaction mixture to incubate longer than the time limit for LISS (e.g. 60 minutes).

If the antiglobulin phase crossmatch is positive (i.e. nonnegative reactions), then the unit is rejected or a least-incompatible crossmatch mode is activated.  The latter requires the transfusion medicine physician to specifically approve the allocation and release of this component.

The following is the Medinfo process I used:

To Be Continued

21/7/20

Processes and Software Building—Part 20

My practice across the globe has exposed me different rationales to performing antibody titration.  In my American training and practice (and also at international institutions following the American version of AABB accreditation), I only routinely performed titration of anti-D for Rh(D) hemolytic disease of the newborn and anti-A/anti-B for ABO-incompatible stem cell transplants AND ABO-incompatible renal transplants.

I have had heated arguments with some physicians who insisted they wanted titers for other antibodies.  The AABB Standards do not require this but leave it to the discretion of the Transfusion Service Medical Director.

In my entire career, I never worked in a blood bank or blood center which had optimal staffing or resources.  I focused on what was medically/technically necessary and even then still had shortages.  If performing a test will not change the clinical treatment, why perform it unless you are doing a research project!

Titration is a time-consuming, and until recently, a tedious manual task.  Recently some of the automated immunohematology analyzers offer a titration program.  We used the Ortho Vision Max which could perform both IgG and IgM titers within one hour—walk away!!  However, during that time, the titration procedure monopolized the analyzer.

The ABO-incompatible renal transplant program at HMC Qatar was modelled after Sweden’s Karolinska Institute.  However the latter site performed manual IgG and IgM titrations using Biorad/Diamed gels.

I did not have sufficient resources to commit staff to manual titration at HMC so I did a comparison study between the Ortho Max and the Biorad methods.  We were able to get good correlation and used the automated method for the transplant.

I am still biased against performing titrations for other antibodies.  I always ask, ‘Does the titration correlate with clinical severity?’  Unlike anti-D, antibodies such as anti-Kell and anti-c may be low titer but cause death.  Can anyone show me a definitive study that titers are useful except for transplants and Rh(D) hemolytic disease of the fetus/newborn?

Since the method was working well on the Ortho equipment, I next established an interface to Medinfo.  The test was performed separately for IgG and IgM antibodies.  Medinfo recorded the reactions in all the wells.  The last well showing a 1+ reaction was interpreted as the titer (e.g. if 1:64 were the last 1+ reaction, then the titer was 64 in Medinfo).

The Medinfo process is shown below.

20/7/20

Processes and Software Building—Part 20

Medinfo software is rules-based so the institution may set its own custom rules for all processes.  One chooses a framework and then adds any additional rules it needs for optimization.  Turnkey systems do not offer this flexibility.

The rules for platelet and plasma components are much simpler than those for RBCs since usually we only consider ABO type.  There are two modes:  regular and emergency, the latter applying if not all the patient testing (including historical checking) is available.  The components, on the other hand, must meet all criteria before being considered for patient use.

Example rules for plasma follow:

For platelets, note that for adults and anyone else >= 20 kg, I gave any type of platelet pool or plateletpheresis component without regard to ABO matching.  With our production method, I did not give Rh immunoprophylaxis to females of child-bearing age receiving platelets from D-positive donors based on our clean (essentially RBC-free) Reveos automated production process.

Similarly, allocation rules for granulocytes, etc. could be made and enforced by the software.  Low-B-titer group A universal plasma would also be easy to implement.

To Be Continued:

19/7/20

Processes and Software Building—Part 19

In the previous post I outlined how Medinfo handled antibody screening and identification.  This post reviews how antigen matching is used based on these results.

There are two modes, regular and emergency.  If the patient has not had at least two ABO/D determinations and/or does not have a recent antibody screen, then emergency mode must be selected with its own rules.  Otherwise, the regular mode applies.

Regular Mode:

In general, if there is a clinically significant antibody, an RBC unit which has not been matched for the corresponding antigen or has the corresponding antigen cannot be routinely selected.  However there is a hierarchy here also:

1. Absolutely prohibited release—no one can override the logic (e.g. giving group O to a patient with anti-H)—not even the transfusion medicine physician can override this
2. Restricted release—only certain staff can release the incompatible or untested unit (e.g. giving C-positive unit to someone with anti-C)
3. Least-incompatible for WAIHA:  requires transfusion medicine physician approval
4. Informational release:  authorized staff may release antigen-incompatible or untested unit but a pop-up menu appears and asks them to accept (e.g. Lewis untested unit in a patient with anti-Lea).
5. Antigen-specificity matched—the usual mode for patients with antibodies

Examples of Regular Mode rules follow (these are not the complete lists but just provided to show the complexity of the process).

Emergency Mode:

This is much more restricted for selection of ABO/D and other antigen typings.  An example follows:

A similar hierarchy exits for platelet and plasma allocation and will be considered in a future post.

To Be Continued:

18/7/20

Processes and Software Building—Part 17

The direct antiglobulin test DAT may be the first or last place that a delayed hemolytic transfusion reaction can be detected.  In my practice, I always performed it the first time I encountered a patient with a positive DAT.  If the subsequent DAT testing is of the same strength and there is no change in the clinical status of the patient, then I might empirically repeat the elution after 14 days, i.e. just when new antibody emergence may be detected.

In summary, my criteria for elution after a positive DAT are:

1. First patient encounter with a positive DAT
2. At least 14 days since the previous elution
3. DAT strength has increased since the previous exam (at least 1+ increase in strength in either IgG or C3)
4. Patient shows evidence of hemolysis
5. Suspected cases of drug-related hemolysis
6. Transfusion Medicine physician specifically orders it otherwise

In the software processes, the following parameters were recorded:

1. Technique of elution (acid glycine, dichloromethane, digitonin, ether, etc.)
2. Number of washes (too many may remove the antibody from the RBCs)
3. Last wash result (must be negative to accept conclusion)
4. Manufacturer of the elution kit (if any)
5. Elution result based on panel testing

Note:

1. All indeterminate or positive eluates would trigger an antibody identification.
2. All results would be reviewed by me or the covering Transfusion Medicine physician.  A comment would be entered into the results that could be viewed by the clinician either directly from Medinfo or through the hospital information system.

If the DAT was only positive for complement, it was up to the Transfusion Medicine Consultant to decide whether to proceed with elution.  Personally, I would usually proceed because the eluate is more concentrated and may occasionally detect an antibody that was not noted in the patient’s plasma.

The attached Medinfo workflow shows the process designed by me for use at HMC Doha.

Tests and Reagents:

There are many variations for this most important test.  In the very least, this consists of:

1. Screening polyspecific AHG for detecting IgG and/or complement
2. If positive, reflex monospecific tests to distinguish IgG from C3 reactivity

There are many kinds of reagents:

1. Immunoglobulin:  whole molecule IgG, monospecific gamma heavy chain, monospecific alpha heavy chain, monospecific mu heavy chain
2. Complement:  C3d, C3c, C3b, C5, etc

Regretfully, some of the monospecific are not really monospecific (e.g. whole molecule IgG detects both heavy and light chains and thus may detect IgG and give weaker results for IgM or even IgA.)

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