Life's Blood
CLASS NOTES

Crossmatch Problems

There are a number of problems that can arise when performing crossmatches

Problems related to number of donors crossmatch when the recipient has an antibody.

If you know a recipient already has an identified antibody or antibodies how would you determine how much blood to screen when a patient has an antibody:

  1. Look up percent of blood compatible with that antibody and if more than one antibody, multiply percentages together.  If you are given the frequency of the antigen, subtract frequency from 100 to get the percent compatible.
     
  2. Divide number of units requested by % compatible to determine how much blood to screen

Example1: Patient has anti-E (70% compatible) and two units are requested to be transfused.

Number of units to be tested to find two units compatible = N

N = 2 units /0.70 = 2.8 (round off to 3)

  • In example 1:  You would set up three units and  two of the three should be compatible.

Example2: Patient has anti-Fya (33% compatible) and anti-S (50% compatible) and four units are requested to be transfused

0.33 x 0.50 = 16.5% compatible

N = 4/0.165 = 24.2

  • In example 2: You would set up 24 units to find 4 compatible units.

Example 3: Patient has anti-c (80% frequency) and two units requested to be transfused.

100 - 80 = 20% compatible

N = 2/0.20 = 10

  • In example 3: You would set up 10 units to find 2 compatible units.

The above formula is only a guideline and there are no guarantees. You may need to screen even more blood.

Clerical and Technical Kinds of Problems

Problem # 1. Blood type is not matching records indicates either a  patient identification problem or sample mix-up.   The steps to solve this problem.

  1. Repeat test
  2. Get new sample if necessary
  3. Change records if necessary

Problem # 2.  Negative Antibody Screening Cells, but crossmatch  is positive or incompatible at immediate spin.  This problems usually signifies some kind of ABO incompatibility. If the reactions are strong, it indicates a major ABO incompatibility.   The main purpose of the Immediate Spin Crossmatch is to catch major ABO incompatibility.  Examples would be crossmatching an A recipient with B donor blood.  Steps to resolve problem 2.

  1. Strong reactions at the immediate spin crossmatch
  • Double-check blood type of recipient and donor unit.
  1. Weaker than 4+ at the immediate spin crossmatch
  • Consider a weak subgroup of A or AB with anti-A1 if the forward and reverse A reactions are weaker than 4+.  This type of positive immediate spin usually reacts just at room temperature.  If the crossmatch is carried through antiglobulin, Coombs, is usually compatible.
     
  • May be due to passive anti-A or B from ABO-incompatible platelets.   If patient is A or B or AB, check recent transfusion history for transfusion of group O platelets because some plasma containing anti-A,B maybe present.  Incompatibility will persist through Coombs - will have to crossmatch group O blood for a few days until passive ABO antibody disappears

Problem # 3.  Negative Antibody Screening Cells, but records show an antibody was previously present.  In this case the titer of antibody has dropped below detectable levels.   Steps to follow for this problem.

  1. You must carry crossmatch through the antiglobulin, Coombs, test. 
  2. You also need  to type donor units for antigen.  The donor units must be negative for the antigen that the recipient formerly had an antibody to.

Problem # 4. Antibody Screening Cells are positive in antiglobulin, Coombs, test and records show a previously identified antibody.   The steps to follow in this situation.

  1. Instead of performing a complete identification panel run selected cells only.  The selected cells will rule out or confirm formation of new antibody.  In order to do this, they must be negative for antigen corresponding to antibody already identified.  If a patient had an anti-K, you would select K negative cells from the panel.
  2. Run an autocontrol with selected cells if not already done with Antibody Screening Cells.
  3. Carry crossmatch through antiglobulin, Coombs, phase and antigen-type compatible donor units

Problem # 5. Antibody Screening Cells are positive in antiglobulin, Coombs, test and no record of a previous antibody.  This could indicate a potentially clinically significant new antibody.  Steps to resolve this problem:

  1. Set up a cell panel to identify the antibody(ies)
  2. Run selected cells as needed to achieve 95% confidence which will be discussed with antibody identification procedure.
  3. Type patient for antigen and it should be negative.
  4.  Carry crossmatch through antiglobulin, Coombs, test
  5. Type compatible donor units for the antigen.  The donor must be negative for the antigen.

Problem # 6.  Antibody Screening Cells positive at room temperature and  negative in antiglobulin, Coombs, testing.   These antibodies are not clinically significant and there is no need to identify the antibody.  If crossmatch positive at room temperature immediate spin, carry the crossmatch through to the antiglobulin, Coombs, phase

Problem # 7.  Antibody Screening Cells  positive at room temperature and in antiglobulin, Coombs, test This is probably due to strong IgM antibody (anti-I, anti-M or -N, anti-Lea or -Leb, anti-P1) which may have activated complement.  The IgM antibody elutes off cells during 37oC incubation, but complement stays on cells, OR strong IgM antibody remains on the cells during 37oC incubation.  Polyspecific Coombs anti-sera reacts with heavily IgM-coated or complement-coated cells in Coombs phase of testing.  Do cell panel to identify antibody.

If IgM antibody present, resolve with prewarm technique on antibody screen and crossmatches:

  1. Warm serum and cells separately before mixing.
  2. Omit Immediate Spin step since this encourages the attachment of IgM antibodies
  3. Omit LISS and continue incubating 20-30 minutes
  4. Wash with warm saline
  5. Use IgG Coombs reagent
  6. If antibody screen and crossmatches are negative after prewarming, no need to give antigen-negative donor blood - just issue crossmatch compatible blood using the prewarm technique

Problem # 8.  Autocontrol is  positive.  If this occurs, perform the following:

  1. Do DAT
  2. Get meds list
  3. Get diagnosis
  4. Get transfusion history
  5. If DAT is positive and patient recently transfused, do elution technique to remove the antibody from transfused donor cells and identify its specificity

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