Compatibility Testing, Crossmatch, Components, and Storage
Key Takeaways
- Compatibility testing starts with patient identification, current specimen validity, ABO/Rh type, antibody screen, and antibody history before choosing a crossmatch method.
- Immediate-spin or validated electronic crossmatch is appropriate only when the antibody screen is negative and there is no clinically significant antibody history.
- A major crossmatch tests recipient plasma or serum against donor red cells; it does not replace antibody identification when the screen is positive.
- Component choice follows the defect: red cells for oxygen-carrying capacity, platelets for platelet number or function, plasma for multiple coagulation factors, and cryoprecipitate for fibrinogen support.
- Storage conditions are exam favorites: red cells at 1-6 C, platelets at 20-24 C with agitation, and frozen plasma or cryoprecipitate with limited post-thaw life.
Compatibility testing as a safety sequence
Compatibility testing is not just the crossmatch. It is a chain of checks that prevents the wrong blood from reaching the wrong patient. On the ASCP MLT exam, the best answer often depends on where the workflow breaks.
A routine red cell compatibility sequence includes patient identification, specimen acceptability, ABO/Rh typing, antibody screen, review of historical antibodies, selection of appropriate donor units, and a compatibility method allowed by policy.
| Safety gate | What it prevents | Exam clue |
|---|---|---|
| Patient and specimen identification | Wrong-blood-in-tube and wrong-patient errors | Mislabeled tube, missing identifiers, discrepancy with history |
| ABO/Rh typing | Acute hemolytic transfusion reaction | Forward/reverse discrepancy or recent emergency group O transfusion |
| Antibody screen | Missed unexpected alloantibody | Positive screen or historical anti-K, anti-Jka, anti-E, etc. |
| Antibody history review | Evanescent antibody risk | Current screen negative but old record positive |
| Crossmatch method choice | Incompatible donor unit release | Electronic or immediate-spin allowed only under defined conditions |
Specimen timing is a frequent exam concept. If the patient has been transfused or pregnant within the preceding 3 months, or if that history is uncertain, the pretransfusion sample must be recent, commonly within 3 days by transfusion service standards and policy. If there is no recent transfusion or pregnancy, local policy controls sample age.
Crossmatch methods
The major crossmatch tests recipient serum or plasma against donor red cells. It asks whether recipient antibodies will react with donor red cell antigens. Routine minor crossmatch is generally not part of modern red cell compatibility testing because donor plasma antibodies are controlled through donor testing and component preparation.
| Patient situation | Appropriate compatibility direction |
|---|---|
| Negative antibody screen and no clinically significant antibody history | Immediate-spin crossmatch or validated electronic crossmatch may be used |
| Positive antibody screen | Identify antibody, select antigen-negative units, and perform required serologic crossmatch |
| Historical clinically significant antibody, current screen negative | Honor history with antigen-negative units and required compatibility testing |
| Unresolved antibody and non-emergent transfusion | Do not release routine units until resolved or referred per policy |
| Life-threatening bleeding before testing complete | Emergency-release workflow with documentation and continued testing |
Electronic crossmatch is not a shortcut for weak documentation. It requires validated computer logic, correct current ABO/Rh results, no current antibody, and no history of clinically significant antibodies. If any of those conditions fails, the exam answer moves back to serologic compatibility testing and antibody-focused unit selection.
ABO compatibility by component
Component compatibility depends on what part of the donor product is clinically important.
| Component | Compatibility principle | Universal emergency concept |
|---|---|---|
| Red blood cells | Donor red cell antigens must be compatible with recipient plasma antibodies | Group O red cells |
| Plasma | Donor plasma antibodies must be compatible with recipient red cells | Group AB plasma |
| Platelets | ABO-identical preferred; substitutions may be used by policy and urgency | No simple universal answer as strong as group O red cells |
| Cryoprecipitate | ABO compatibility preferred but lower plasma volume makes policy important | Use according to inventory, urgency, and policy |
For red cells, group O is the classic emergency donor type because O red cells lack A and B antigens. For plasma, group AB is the classic universal donor plasma because AB plasma lacks anti-A and anti-B. Platelets are more nuanced. ABO-identical platelets usually give better increments, but inventory and urgency often drive substitutions. Rh immune globulin may be considered for Rh-negative patients, especially females of childbearing potential, who receive Rh-positive platelet components containing red cell contamination.
Component selection
The exam often gives a clinical problem and asks which product fixes it.
| Clinical problem | Best product direction | Common trap |
|---|---|---|
| Symptomatic anemia or acute blood loss needing oxygen-carrying capacity | Red blood cells | Plasma does not correct anemia |
| Thrombocytopenia or platelet dysfunction with bleeding or procedure need | Platelets | Red cells do not correct platelet number |
| Multiple coagulation factor deficiency with bleeding, massive transfusion, or urgent warfarin reversal when indicated | Plasma or factor-specific therapy per policy | Plasma is not a volume expander |
| Low fibrinogen with bleeding, obstetric hemorrhage, trauma, or DIC | Cryoprecipitate or fibrinogen concentrate by policy | Platelets do not replace fibrinogen |
| Need to reduce febrile reactions, HLA alloimmunization, or CMV transmission risk | Leukocyte-reduced component | Washing and leukoreduction solve different problems |
| Recurrent severe allergic reaction or IgA deficiency concern | Washed red cells or washed platelets when available | Leukoreduction does not remove most plasma proteins |
| Risk for transfusion-associated graft-versus-host disease | Irradiated cellular component | Irradiation does not prevent all febrile reactions |
Irradiation is used for selected cellular components to prevent transfusion-associated graft-versus-host disease. It is important for intrauterine transfusion, congenital cellular immunodeficiency, hematopoietic progenitor cell transplant settings, and other policy-defined high-risk patients. Washed components reduce donor plasma proteins. Leukocyte reduction removes most donor white cells and lowers febrile nonhemolytic reaction risk, HLA alloimmunization risk, and CMV transmission risk.
Storage and expiration patterns
Storage questions are high-yield because they test product safety. Know the basic ranges and the reason behind them.
| Component | Typical storage condition | Exam reason |
|---|---|---|
| Red blood cells | 1-6 C refrigerated | Preserves red cell viability and limits bacterial growth |
| Platelets | 20-24 C with continuous gentle agitation | Maintains platelet function but increases bacterial contamination concern |
| Fresh frozen plasma and plasma frozen within 24 hours | Frozen; thawed before transfusion | Preserves coagulation factors while frozen; post-thaw time is limited |
| Cryoprecipitate | Frozen; thawed before transfusion | Concentrated fibrinogen support with limited post-thaw life |
| Frozen/deglycerolized red cells | Frozen for rare units, then deglycerolized before transfusion | Preserves rare phenotypes but requires special processing |
The exam rarely needs exact expiration dates for every additive system. It does expect you to know that platelets are room temperature components with bacterial risk, red cells are refrigerated, and thawed plasma or cryoprecipitate has a limited post-thaw window under standards and local policy.
A patient has a negative antibody screen and no history of clinically significant antibodies. Which compatibility method may be acceptable under a validated transfusion service policy?
A patient has a documented history of anti-Jka from a prior admission. The current antibody screen is negative. What is the safest red cell selection?
Match the component with the best exam-level use or storage clue.
Match each item on the left with the correct item on the right