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Crossmatching and issuing blood

16 min

Skills you'll build4 skills
  • Choose an immediate-spin or antiglobulin crossmatch from the patient's antibody history
  • Determine eligibility for the validated electronic-crossmatch pathway
  • Verify a component at issue and state any testing still incomplete
  • Read column and solid-phase results using platform-specific endpoints

At the bench: Use the antibody workup to select suitable donor units · Check component identity, storage, and suitability before issue

Try first

Try first

A patient's record lists anti-Fya identified in 2022. Today's antibody screen is nonreactive, and Fy(a−) units have been selected. Which crossmatch does each unit need?

Keep going to see the reasoning.

Keep going to see the reasoning.

Keep going to see the reasoning.

Right. Keep going to follow the reasoning.

Keep going to see the reasoning.

Get the idea

Use the explanation to check your first decision.

Choosing the crossmatch method

The crossmatch tests the recipient's plasma against the red cells of the unit to be given.1,2 The method depends on the antibody screen and the patient's record:1,3

  • Screen nonreactive and no history of a clinically significant antibody. An immediate-spin crossmatch or a validated electronic crossmatch detects ABO incompatibility.
  • A current or past clinically significant antibody. Antigen-negative units are crossmatched through the antiglobulin phase.

An immediate-spin crossmatch is read right after centrifugation at room temperature. An IgG antibody against a donor antigen needs incubation and antiglobulin reagent to be detected, so an immediate-spin crossmatch can appear compatible and miss it.1

The electronic crossmatch

In an electronic crossmatch, a validated computer system confirms ABO compatibility without mixing plasma and cells. FDA guidance expects all of these:4

  1. The unit's ABO and D confirmed and entered in the system.
  2. The recipient's ABO and D determined twice, once on the current specimen and once more, preferably from a prior record or a separately collected specimen.
  3. A nonreactive current antibody screen and no history of a clinically significant antibody.
  4. No unresolved ABO discrepancy.

A patient who does not meet every condition needs a serologic crossmatch.3,4

Checks at issue

The person issuing a unit checks the recipient's two identifiers, the donation identification number, the component, the compatibility interpretation, special requirements and the expiration. The unit is inspected for abnormal color, clots and leaks.1,3 Any discrepancy stops the issue until it is resolved. Units released in a life-threatening emergency before testing is complete are issued under the emergency-release procedure, with a physician's signed justification. The record states which testing is incomplete, and the testing is finished promptly.2,3

Reading reactions by test method

Positive and negative reactions look different in each test method.5,6

MethodPositiveNegative
TubeAgglutination or hemolysisCells disperse evenly
Column agglutinationAgglutinates trapped at the top of the gel or through itA compact pellet at the bottom
Solid phase, Protein A formatA smooth layer of cells across the wellA compact button in the center

In a column, a mixed-field reaction shows agglutinated cells in the gel and a pellet at the bottom.5

Follow the bench demonstration

Sources for this step
References
  1. Bloch EM, Campbell-Lee S, McKenna DH Jr, Montemayor-Garcia C, Schwartz J, Shaz B, Storry J, eds. Technical Manual. 22nd ed. AABB; 2026.
  2. Compatibility testing, 21 CFR §606.151 (2026). Accessed September 27, 2026. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-F/part-606/subpart-C/section-606.151
  3. Association for the Advancement of Blood & Biotherapies. Fundamental Standards for Blood Collection and Transfusion. 2nd ed. AABB; 2025. Accessed September 27, 2026. https://www.aabb.org/docs/default-source/default-document-library/standards/fundamental-standards-for-blood-collection-and-transfusion-2nd-ed.pdf?sfvrsn=caa34314_3
  4. US Food and Drug Administration. Computer Crossmatch: Computerized Analysis of the Compatibility Between the Donor's Cell Type and the Recipient's Serum or Plasma Type. Guidance for Industry. April 2011. Accessed September 27, 2026. https://www.fda.gov/media/80857/download
  5. Diagnostic Grifols, SA. DG Gel 8 Cards Instructions for Use. US Food and Drug Administration. Accessed September 27, 2026. https://www.fda.gov/media/188548/download
  6. Bio-Rad Medical Diagnostics GmbH. Solidscreen II Microplate for Solid Phase Antiglobulin Tests With TANGO Instruments Instructions for Use. US Food and Drug Administration. Accessed September 27, 2026. https://www.fda.gov/media/124013/download

Watch one

Read each decision and its explanation.

A man is scheduled for hip surgery, and the surgeon requests 2 units of red cells.

  • Today's specimen types group A, D-positive. The antibody screen is nonreactive.
  • The laboratory information system has a group A, D-positive result on file from a specimen collected in March 2025, and no antibody history.
  • The electronic crossmatch system is validated, and the group A units in stock had their ABO and D confirmed on receipt.

Can his units be issued by electronic crossmatch?

  1. Check identification first. The specimen label and the request have the same two identifiers.

    The electronic crossmatch relies on the records, so a specimen from the wrong patient makes it unsafe.

  2. Compare the two ABO and D results. Today's group A, D-positive agrees with the March 2025 record.

    A second determination guards against a specimen drawn from the wrong patient.

  3. Read today's screen. It is nonreactive.

    A reactive screen needs antibody identification and a serologic crossmatch.

  4. Check the antibody history. There is none.

    An antibody below detection today can still return after exposure.

  5. Check the units and the system. The unit ABO and D were confirmed, and the system is validated.

    The computer can only confirm compatibility from confirmed unit data.

Yes. He meets every condition, so the system can confirm ABO compatibility and the units can be issued by electronic crossmatch.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

In a Protein A solid-phase antibody screen, well 1 shows a small compact button of red cells in the center. Well 2 shows red cells spread as a smooth layer across the bottom. How are the wells read?

In this solid-phase format, a compact central button is unbound cells that rolled to the center. Well 1 reads negative, and the smooth layer in well 2 reads positive.

Read a solid-phase well by tube agglutination criteria

Each platform shows a positive reaction differently. In column agglutination, agglutinates stay in the gel and negative cells form a bottom pellet. In a Protein A solid-phase well, a smooth layer across the well is positive and a compact central button is negative, so reading solid phase by tube criteria misreads the result.

Sensitized cells bind across the coated well and form a smooth layer. Unsensitized cells roll to the center as a compact button.

Every well contains red cells. The reading depends on where the cells collect.

Hint
  1. In this format, sensitized cells attach to the coating of the well.
  2. Ask which cells are still free to collect in the center when the plate is centrifuged.

Review Column agglutination

Problem 2 of 3 · Hints available

A woman's specimen types group O, D-positive, with a nonreactive screen and no antibody history. She has never been tested at this hospital, and no second specimen has been drawn. The surgeon asks for units by electronic crossmatch. What does the laboratory do?

Her ABO and D have been determined once. The electronic crossmatch requires a second determination that agrees.

A single determination cannot detect a specimen drawn from the wrong patient. A second agreeing result allows the electronic crossmatch, and an immediate-spin crossmatch checks ABO compatibility until then.

Emergency release is for a life-threatening emergency when testing cannot wait. Her surgery is planned, and a serologic crossmatch can be done now.

Hint
  1. Count the ABO determinations on file for her.
  2. Ask what the guidance expects besides a nonreactive screen and no antibody history.

Review Electronic crossmatch

Problem 3 of 3 · On your own

At issue, the unit label and the compatibility tag agree. The tag shows the recipient's MRN as 0487213, and the request form shows 0487231. The name is the same on both. What do you do?

A name is one identifier. The MRN is the second, and it disagrees, so the link between the tested specimen and this patient is broken.

It is not yet known which number is correct. Changing a record to make it match hides the error.

The bedside check is the final safeguard and does not replace a complete match at issue.

Every identifier must agree before a unit leaves. The discrepancy is investigated, and the unit is issued once the records agree.

Review Inventory planning and final verification

Use it

Read the case evidence, then make each decision. The step is complete without it.

  • Dmitri Blank, 29, a bike courier (MRN 7719026), arrives after a crash, bleeding heavily. The trauma physician orders 4 units of red cells at once.
  • A specimen is drawn and sent before the first unit is hung.
  • The blood bank issues 4 group O, D-negative units under emergency release.
  • Forty minutes later his specimen types group A, D-positive.
  • His antibody screen by column agglutination: screening cell I leaves a compact pellet at the bottom of the gel. Screening cell II leaves a band of agglutinates at the top.
Decision 1 of 3

How does the issue record describe the 4 emergency units?

Group O red cells address ABO compatibility only. His antibody screen had not been done, and calling the units compatible hides that from the care team.

Described emergency-release blood as fully tested

Emergency-release units are issued before compatibility testing is complete, often as group O red cells. Labeling them compatible hides that risk from the care team and can stop the testing that would find an antibody, so the issue record states which tests are incomplete and the laboratory completes them promptly.

The issue record is made when the units leave. Leaving it blank loses the link between these units and this patient.

The record states what was not done when the units left. The laboratory then completes the testing and reports what it finds.

Review Inventory planning and final verification

Decision 2 of 3

How is his screen read?

Agglutinates are too large to pass the gel and stay at the top, a strong positive. The pellet in cell I shows cells that passed through the gel.

In a column, unagglutinated cells pass through the gel to a pellet at the bottom. The pellet in cell I is negative.

Hemolysis is a tube endpoint. In a column, the reaction is read from the position of the cells.

Review Column agglutination

Decision 3 of 3

More units are ordered. What is the next compatibility step?

Immediate spin would miss the IgG antibody that his screen just showed. Units for him need an antiglobulin crossmatch.

Used immediate spin to rule out IgG incompatibility

An immediate-spin crossmatch detects ABO incompatibility. For a patient with a current or historical clinically significant antibody, an IgG antibody against a donor antigen reacts at the antiglobulin phase, so an immediate-spin crossmatch can look compatible and miss it.

A reactive screen excludes the electronic crossmatch. The antibody must be identified first.

Units must lack the antigen the antibody targets. The retrospective crossmatch shows whether any unit already given was incompatible, and that result is reported to the physician at once.

Review Crossmatch and issue

The band of agglutinates at the top of the gel for cell II showed an antibody that the emergency units were not tested against. His issue record lists the incomplete testing, and every unit from now on needs antigen-negative selection and an antiglobulin crossmatch.

For reference

Sources checked