Free ASCP MLS Blood Banking Exam Mock Test – Part 61: Compatibility Testing and Crossmatching

In a massive transfusion protocol (MTP), the goal is to replace blood volume and maintain coagulation function by approximating whole blood composition.
This typically involves Red Blood Cells (RBCs), Fresh Frozen Plasma (FFP), and Platelets in a balanced ratio (often close to 1:1:1 for RBC:FFP:Platelets).

Looking at the options:

• a) Cryoprecipitated AHF and Apheresis Platelets, Irradiated → Cryo is not routinely given in initial MTP; it’s for fibrinogen replacement if needed later.

• b) Fresh Frozen Plasma and Apheresis Platelets → Yes, this matches standard MTP component use alongside RBCs.

• c) Deglycerolized RBCs and FFP → Deglycerolized RBCs are for special cases (e.g., IgA deficiency), not routine MTP.

• d) Granulocytes and Cryoprecipitated AHF → Granulocytes are rarely used and not part of standard MTP.

The major crossmatch mixes the recipient’s serum (which contains antibodies) with the donor’s red cells. Its primary purpose is to ensure there are no clinically significant antibodies in the recipient that would react with and destroy the donor’s red cells after transfusion, preventing an acute hemolytic transfusion reaction

A minimum of two independent patient identifiers (such as full name, medical record number, and/or date of birth) are required on a sample tube at the time of collection. This is a critical safety standard to prevent misidentification and ensure the sample is correctly matched to the right patient for testing and transfusion.

Incorrect options:

• (a) One → insufficient; too high risk of mix-up.

• (c) Three and (d) Four → more than required; not mandated by standards.

In an emergency when there is immediate need for blood and there is no time to complete a type and screen or crossmatch, uncrossmatched group O blood (preferably O negative for women of childbearing potential) is used.

Incorrect options:

• (b) Known antibodies → must match with antigen-negative units, not uncrossmatched O blood.

• (c) Only Rh-negative units available → not the reason; that’s a choice for specific patient groups.

• (d) Low platelet count → unrelated; platelet transfusion, not RBC transfusion.

The immediate-spin (IS) crossmatch is a rapid compatibility test performed at room temperature, where recipient serum/plasma is mixed with donor red cells and centrifuged immediately.

It detects agglutination due to ABO incompatibility, which is caused by naturally occurring IgM antibodies that react at room temperature.

Incorrect options:

• (b) Rh typing errors → determined by Rh typing, not crossmatch.

• (c) IgG antibodies → detected in antiglobulin (AHG) crossmatch, not IS crossmatch.

• (d) Enzyme-sensitive antibodies → require enzyme-treated panel testing, not IS method.

When the seal of a Red Blood Cell (RBC) unit is broken — for example, during pooling, aliquoting, or attaching an open system — the product is no longer sterile.

Therefore, it must be used or discarded within a limited time period to prevent bacterial contamination.

AABB standard:

• If stored at 1–6 °C after the seal is broken → maximum storage = 24 hours.

• If stored at 20–24 °C (room temperature) → maximum storage = 4 hours.

A “crossmatch compatible” unit means that the recipient’s serum (or plasma) did not react (no agglutination or hemolysis) with the donor’s red blood cells during the crossmatch test.

the incorrect options:

• (b) Strong positive reaction → means incompatible.

• (c) Donor sample is antigen-positive → unrelated; crossmatch doesn’t identify donor antigen status.

• (d) Patient has no antibodies at all → not necessarily true; they may have antibodies that simply don’t react with this particular donor’s cells.

The Immediate Spin (IS) phase of a crossmatch is a rapid room-temperature test that mixes the recipient’s plasma/serum with the donor’s red cells, then centrifuges immediately and checks for agglutination.

• It is designed to detect ABO incompatibility, which is mainly caused by naturally occurring IgM antibodies that react at room temperature.

• If agglutination occurs, it indicates that the recipient’s plasma contains anti-A or anti-B antibodies incompatible with the donor’s red cells.

Why not the others:

• (a) Detecting clinically significant alloantibodies → done in the antiglobulin (AHG) phase, not the IS phase.

• (c) Verifying correct recipient sample → ensured by identification procedures, not by crossmatching.

• (d) IS phase does detect IgM antibodies, but the purpose is specifically to detect ABO incompatibility, not just any IgM alloantibody.

A transfusion request typically needs:

• Recipient identifiers (usually two, to ensure correct patient identification)

• Name of ordering physician

• ABO and Rh of the component requested (so the blood bank can issue a compatible unit)

• Date and time of transfusion (often required, but not listed here)

• Date blood typing was performed — this is not usually required on the transfusion request form because the blood bank already has the patient’s type on file or will retest; it’s more relevant to the lab records.

A typical response to one unit of Apheresis Platelets (Leukocyte-Reduced) in an adult (≈70 kg) is an increase of 30,000–60,000/µL in the platelet count within 1 hour after transfusion.

Here:

• Pre-transfusion count: 10,000/µL

• Post-transfusion count: 50,000/µL
  → Increment: +40,000/µL ✅

This is within the expected range, showing a normal and effective platelet transfusion response.

Incorrect options:

• (a) HLA antibodies → would cause poor platelet increment (refractoriness).

• (b) Active bleeding → would lower post-transfusion count.

• (d) Pre-transfusion error → unnecessary; values are consistent.

The indirect antiglobulin crossmatch (IAT crossmatch), also known as the AHG crossmatch, is designed to detect clinically significant IgG antibodies in the recipient’s serum that may react with donor red cell antigens.

Incorrect options:

• (a) Cold agglutinins → usually IgM, react at room temperature, not 37 °C.

• (b) IgM antibodies only → detected by immediate-spin, not AHG.

• (d) ABO discrepancies → resolved by ABO typing, not crossmatch.

Red Blood Cell (RBC) units must be maintained between 1–10 °C during storage and transport.

• The unit was returned at 12 °C, which exceeds the acceptable upper limit.

• Even though it was unentered and returned within 1 hour, the temperature criterion was violated — so the blood’s safety cannot be guaranteed.

Option review:

• (a)  Incorrect — units can be returned if all criteria are met (time, temperature, integrity).

• (b) Correct — temperature exceeded 10 °C, so it must be discarded.

• (c)  Being unentered doesn’t override temperature requirements.

• (d) Visual acceptability and attached segments don’t ensure product safety if temperature limits were breached.

The patient is phenotype A₂B and has made anti-A1, meaning they can react against ordinary A₁ or A₁B donor blood.

• Since A₂B units are unavailable, you cannot give type A or AB blood (except A₂B itself).

• The safest choice is type O (lacks A and B antigens), and Rh-negative is chosen to avoid Rh immunization if the patient’s Rh type is unknown or is Rh-negative.

• B, Rh-positive or negative (options a and b) would still cause an ABO mismatch because the patient is A₂B, not B.

The final bedside check immediately before transfusion is a critical safety step to prevent misidentification errors. It requires two qualified individuals to independently verify that the information on the blood product label (unit number, blood type) exactly matches the patient’s identity using two unique identifiers (e.g., patient’s full name and medical record number or date of birth). This is a mandatory procedural standard.

Incorrect options:

• (b) Checking vital signs is essential before and during transfusion, but not the key double-check step.

• (c) Reviewing medical records is done earlier, during ordering — not at bedside.

• (d) Baseline labs are not required immediately before every transfusion.

All listed errors can cause a false-positive crossmatch:

• a) Dirty glassware/contaminated reagents: Can introduce particles that cause non-specific agglutination.

• b) Cold autoantibody interference: These antibodies can react at room temperature, causing agglutination that is not clinically significant for transfusion at 37°C.

• c) Incorrect temperature: Performing the test at too low a temperature can allow cold agglutinins to react.

A positive crossmatch means incompatibility between the donor’s red cells and the recipient’s serum/plasma.

This occurs when the recipient has an antibody that reacts with an antigen on the donor’s red cells — indicating that transfusing that unit could cause a hemolytic transfusion reaction.

Incorrect options:

• (a) Compatibility → opposite of correct.

• (c) Lack of antibody detection → describes a negative crossmatch.

• (d) Technical error → possible but not the definition of a positive result.

Compatibility (crossmatch) testing is required only for blood components that contain red blood cells, because that’s where antigen–antibody reactions can cause hemolytic transfusion reactions.

Incorrect options:

• (b) Whole blood → must be crossmatched.

• (c) Positive antibody screen → requires additional compatibility testing.

• (d) Red cells → must be crossmatched before transfusion.

When Red Blood Cells (RBCs) are irradiated, their expiration date changes because irradiation damages cell membranes and reduces storage stability.

Key rule (AABB standard):

• After irradiation, RBCs expire 14 days from the date of irradiation, or on their original outdate — whichever comes first.

The core of the major crossmatch is testing the recipient’s serum/plasma (which contains antibodies) against the donor’s red blood cells (which have antigens). This is done to detect any antibodies in the recipient that could react with and destroy the transfused donor red cells, ensuring compatibility.

Incorrect options:

• (b) Donor’s plasma → used in minor crossmatch (no longer routinely done).

• (c) Another patient’s cells → irrelevant; not used in transfusion testing.

• (d) Reagent red cells only → used in antibody screening, not crossmatching.

Even though the current antibody screen is negative, a history of a clinically significant antibody (like anti-Jkᵇ) must always be honored.

The Kidd (Jk) antibodies are known for being weak, transient, and sometimes undetectable after some time — yet they can cause delayed hemolytic transfusion reactions if the patient is given antigen-positive blood.

Incorrect options:

• (a) Phenotyping the patient’s cells is unnecessary once the antibody specificity is known.

• (b) A cell panel isn’t needed — the antibody has already been identified.

• (c) ABO type-specific crossmatch alone ignores the antibody history — unsafe.

One unit of apheresis platelets (which contains approximately 3–6 × 10¹¹ platelets) is expected to increase the platelet count in a 70-kg adult by 30,000 to 60,000/µL. The most commonly cited and expected range in clinical guidelines is 30,000–50,000/µL.

• Neonates under 4 months have immature immune systems and do not produce significant levels of ABO antibodies (reverse typing unreliable) or unexpected alloantibodies (antibody screen not required).

• Forward typing (cell grouping) determines the ABO group from their red cell antigens.

• Rh(D) typing is critical to prevent hemolytic disease of the fetus and newborn (HDFN) and to provide Rh-compatible blood.

• Reverse typing and antibody detection are not routinely performed on neonatal samples.

• Incompatible at IAT phase with antibody detection cells means an antibody is present in the patient’s serum.

• Incompatible with some donor units (2 of 6) suggests the antibody is directed against a specific antigen present in those donors and the screen cells.

• An alloantibody explains this pattern: it reacts with cells containing the corresponding antigen, but not all random donors will be positive for that antigen.

• An autoantibody (b, d) would typically react with all cells tested, including all donor units and the patient’s own cells.

The electronic (computer) crossmatch is a paperless compatibility check performed by validated computer systems instead of serologic testing.

It ensures that the donor and recipient are ABO compatible using stored, verified test results — only when no antibodies are present.

Incorrect options:

• (a) Positive antibody screen →  requires serologic crossmatch.

• (b) Clinically significant antibodies →  not eligible for electronic crossmatch.

• (d) Different Rh types → not a disqualifier; Rh mismatch may be acceptable with proper labeling.

An electronic crossmatch relies on computer software to verify ABO compatibility between a donor unit and a recipient. It replaces the physical serologic crossmatch (immediate-spin, 37°C incubation, and AHG phases) when specific criteria are met (e.g., a negative antibody screen). No test tubes or reagents are used for the crossmatch itself.

In emergency transfusions where the patient’s blood type is unknown, Group O blood is used because it lacks A and B antigens, minimizing the risk of ABO incompatibility.

However, Rh (D) type is also critical—especially for females of childbearing age:

• O negative blood is preferred because it is both ABO- and Rh-compatible with all types.

• Using O positive blood could expose an Rh-negative woman to the D antigen, leading to Rh sensitization and risk of hemolytic disease of the newborn (HDN) in future pregnancies.

Other options:

• (a) O positive → acceptable for males or postmenopausal women in emergencies, but not for women of childbearing potential.

• (c) A positive and (d) B negative → incompatible with unknown ABO types.

• The patient has low Hb 3 weeks post-transfusion → possible delayed hemolytic transfusion reaction (DHTR).

• DAT 1+ mixed field means some cells (likely the transfused donor cells) are coated with antibody.

• The antibody screen is negative now because the alloantibody may be too low to detect in serum but is attached to donor RBCs.

• Elution can remove antibody from the RBCs and identify the specificity, confirming a DHTR.

ABO and Rh typing is the foundational first step in pretransfusion testing. The results determine the type of blood that can be safely selected for the patient. All subsequent tests, like the antibody screen and crossmatch, rely on and are interpreted in the context of the patient’s known ABO and Rh type.

A computer (electronic) crossmatch may be performed only when:

• The patient’s current antibody screen is negative, and

• There is no history of clinically significant antibodies on record.

This ensures there is no risk of an undetected antigen–antibody incompatibility. The electronic system simply verifies ABO/Rh compatibility between donor and recipient records.

Option review:

• (a)  A historical ABO/Rh record is required in addition to a negative antibody screen, but this alone is not sufficient.

• (b)  The computer system’s manual stating it’s acceptable is not a clinical requirement — regulations govern usage, not manuals.

• (c) Correct — the absence of clinically significant antibodies is the key requirement.

• (d)  An immediate spin crossmatch is not needed if an electronic crossmatch is properly validated.

If the initial test for the D antigen is negative, weak D testing must be performed. This involves adding an antiglobulin (Coombs) reagent to detect the presence of a small number of D antigens (weak D). This confirmation is critical to determine if a patient is truly Rh-negative or a weak D positive, which affects what blood products they can receive.

Incorrect options:

• (b) Direct antiglobulin test (DAT) → detects in vivo sensitization of red cells, not for Rh confirmation.

• (c) Auto control → checks for autoantibodies; unrelated to Rh typing.

• (d) Enzyme test only → not used for routine Rh confirmation.

Each unit of Red Blood Cells is expected to raise the hemoglobin by approximately 1 g/dL (or the hematocrit by about 3%) in an average-sized adult.

• Pre-transfusion Hb: 7.0 g/dL

• Increase from 2 units: 2 units × 1 g/dL/unit = 2.0 g/dL

• Expected post-transfusion Hb: 7.0 + 2.0 = 9.0 g/dL

Crossmatching is done to ensure compatibility between donor red cells and recipient antibodies.
To detect any antibodies that could react with donor antigens, the patient’s plasma or serum must be used — since that’s where the antibodies are found.

Incorrect options:

• (a) Fresh donor samples only → not required; donor cells from the blood unit are used.

• (c) Saline solution → used as a medium or wash, not for crossmatching itself.

• (d) Red cell stroma → not used in serologic testing.

In a compatibility test (crossmatch), the recommended red cell suspension is about 2–5%.

If a 10% red cell suspension is used:

• There are too many red cells (antigen excess) relative to the antibody in the serum.

• When antigen is in excess, antibodies cannot effectively bridge between red cells to cause agglutination.

• This leads to a false-negative result — agglutination fails even though the antibody is present.

For Red Blood Cell transfusions, the safest practice is to transfuse ABO-identical blood. While O positive is often called a “universal donor” for red cells in emergencies for Rh-positive recipients, the safest and standard practice is to give O positive blood only to O positive recipients. This avoids the risk of sensitizing an Rh-negative person to the D antigen.

For patients who have been pregnant or transfused within the past 3 months, their immune system may be stimulated to produce new antibodies. To ensure the antibody screen reflects their current immune status, standards require the pretransfusion sample to be collected within 72 hours (3 days) of the scheduled transfusion. This minimizes the risk of a missed, newly-formed antibody.

A minor crossmatch is the reverse of the major crossmatch.
It tests whether antibodies in the donor’s plasma (or serum) could react with antigens on the recipient’s red blood cells.

Incorrect options:

• (b) Donor serum with donor cells → meaningless (autologous).

• (c) Recipient serum with donor cells → major crossmatch.

• (d) Serum from both together → not a valid test procedure.

Washed Red Blood Cells are used to prevent severe allergic or anaphylactic reactions, particularly in IgA-deficient patients who have anti-IgA antibodies. Washing removes nearly all the plasma proteins, including IgA, which is the cause of the reaction.

• (a) HDN is managed with RhIG, not washed cells.

• (c) A positive DAT with autoantibody is not an indication for washing.

• (d) A low hematocrit alone is not an indication for washed cells.

This combination provides a complete and standard ABO grouping for pretransfusion testing, allowing for a cross-check between the forward and reverse groupings to ensure accuracy and detect any discrepancies.

Why the other options are incorrect:

• a) Includes Anti-A,B (which is not routinely required for basic ABO grouping as its reaction is covered by Anti-A and Anti-B) and O cells (which are used as a negative control in other tests like antibody screens, not in the basic ABO group).

• b) Includes A2 cells, which are not part of a routine ABO group. They are used for special investigations to rule out subgroups like A2 with anti-A1.

• d) Includes both unnecessary reagents: Anti-A,B and A2 cells.

A positive direct antiglobulin test (DAT) means the patient’s red cells are already coated with antibodies or complement in vivo.

During compatibility testing (crossmatching), this coating can cause incompatible reactions with all donor cells, even if the donor blood is actually compatible — because the patient’s red cells are already sensitized.

Let’s review the options briefly:

• (a)  Correct — the patient’s sensitized cells cause pan-reactivity, making all crossmatches appear incompatible.

• (b)  Incorrect — the weak D test involves testing Rh antigens, not affected by a positive DAT.

• (c)  Not necessarily — the antibody screen detects free (unbound) antibodies in serum; in a DAT-positive case, antibodies may be bound, so the screen could be negative.

• (d)  ABO discrepancies occur for other reasons (e.g., rouleaux, weak subgroups), not typically from a positive DAT.

A negative crossmatch result means that no agglutination or hemolysis was observed. This indicates that no detectable serologic incompatibility exists between the recipient’s serum (antibodies) and the donor’s red blood cells (antigens), and the unit is considered safe to transfuse.

Incorrect options:

• (b) Weak antibody present → would likely cause at least weak reactivity, not a true negative.

• (c) Invalid test result → unrelated; negative means valid and compatible.

• (d) Donor blood unsuitable → incorrect; a negative crossmatch means the unit is suitable.

To prepare platelet concentrates from whole blood, a two-step centrifugation process is used:

1. Light spin (soft spin):

   • Purpose: To separate platelet-rich plasma (PRP) from red cells and most white cells.

   • The top layer (PRP) is expressed into a satellite bag.

2. Hard spin (heavy spin):

   • Purpose: To concentrate the platelets by sedimenting them from the PRP.

   • The supernatant (platelet-poor plasma) is removed, leaving the platelet concentrate.

This light spin → hard spin sequence yields viable platelets suitable for transfusion.

 Other options:

• (b) Two hard spins — would damage platelets.

• (c) Two light spins — wouldn’t concentrate platelets adequately.

• (d) Hard spin then light spin — incorrect order; platelets would be lost in the initial hard spin.

According to transfusion service standards (such as AABB guidelines):

• A pretransfusion sample is valid for 72 hours (3 days) from the time of collection if the patient has been recently transfused or if the transfusion history is unknown.

• This time limit ensures detection of any new antibodies that may develop after recent exposure to foreign red cell antigens.

Why not the others:

• (a) Wednesday 4:00 PM → only 24 hours (too short)

• (b) Thursday 11:59 PM → only 2 days later (too short)

• (d) Saturday 4:00 PM → exceeds 72 hours (too long)

ABO incompatibility causes the most severe and potentially fatal transfusion reactions because:

• Naturally occurring IgM antibodies (anti-A and/or anti-B) are strongly hemolytic.

• They activate complement efficiently, leading to intravascular hemolysis, hemoglobinuria, renal failure, shock, and even death.

• These reactions can occur immediately — often within minutes of transfusion.

Other antibody reactions:

• (b) Rh mismatch → Usually causes delayed hemolytic reactions or hemolytic disease of the newborn, not acute intravascular hemolysis.

• (c) Kell antibodies → Clinically significant but cause extravascular, not immediate, hemolysis.

• (d) Kidd antibodies → Can cause delayed hemolytic reactions, often mild to moderate.

The standard pretransfusion testing procedure, often called a “type and screen” or “type and cross,” consists of:

1. ABO and Rh typing of the patient.

2. Antibody screen (IAT) on the patient’s serum.

3. Crossmatch between the patient’s serum and the donor red blood cells.

Compatibility testing (commonly referred to as crossmatching) is done before transfusion to ensure donor blood is compatible with the recipient. It typically includes:

• ABO and Rh typing of both donor and recipient

• Antibody screen (detection of clinically significant unexpected antibodies)

• Crossmatch (major and minor in the past, now mostly immediate spin or electronic if antibody screen negative)

The crossmatch, or major crossmatch, is a compatibility test where the recipient’s serum (which contains antibodies) is tested against the donor’s red blood cells (which have antigens). Its purpose is to detect any antibodies in the recipient that could react with and destroy the transfused donor red cells.

Incorrect options:

• (a) Donor serum vs. recipient RBCs — reverse of what’s done.

• (c) Genetic analysis — not part of transfusion testing.

• (d) Infectious disease screening — performed separately on donor blood.

The final bedside check immediately before transfusion must include verifying:

• Patient identity (not listed explicitly here, but implied in real checks)

• Donation ID number on the unit against the paperwork and patient’s wristband

• Donor ABO and Rh (to ensure compatibility)

This is critical to prevent mistransfusion. The other options, while relevant earlier, are not part of this final immediate pre-transfusion verification.

Crossmatching is the mandatory final step before issuing blood for transfusion. It is a safety test that confirms compatibility between the specific donor unit and the specific recipient, designed to prevent a hemolytic transfusion reaction.

Incorrect options:

• (b) Plasma glucose testing → unrelated to transfusion safety.

• (c) Platelet count → not required before RBC transfusion.

• (d) Coagulation screening → relevant to plasma or platelet therapy, not for issuing RBCs.

EDTA is the most common anticoagulant used in the lavender-top tubes used for collecting patient blood samples for pretransfusion testing (including crossmatch). It effectively prevents clotting by binding calcium and is suitable for blood bank serological testing.

Incorrect options:

• (b) CPD → used as the anticoagulant in blood collection bags for donor blood units, not for testing samples.

• (c) Heparin → may interfere with some serologic reactions; not recommended for crossmatch testing.

• (d) Sodium fluoride → used for glucose testing, not blood banking.

An incompatible antiglobulin crossmatch occurs when the recipient’s serum reacts with the donor’s red cells during the antiglobulin phase.

If the donor’s red cells have a positive DAT, they are already coated with antibody or complement. When the antiglobulin reagent is added in the crossmatch, it will react with this pre-existing coating, causing a positive reaction (incompatibility) even if the recipient has no antibodies against the donor.

The other options are incorrect because:

• (a) & (c) involve the recipient’s red cells, which are not tested in the major crossmatch.

• (b) involves the donor’s serum, which is not tested in the major crossmatch.

The most common and dangerous errors in transfusion medicine are clerical errors. This includes mislabeling the patient’s sample tube, drawing blood from the wrong patient, or incorrectly identifying the patient at the bedside. These mistakes can lead to a patient receiving ABO-incompatible blood, causing a severe or fatal hemolytic transfusion reaction.

Other options:

• (b) Incorrect reagent preparation → can cause false test results but is less common.

• (c) Contaminated saline → may cause technical errors, not clerical.

• (d) Instrument malfunction → rare and usually detected by built-in checks.

The patient is AB, Rh-negative.

• In a life-threatening hemorrhage, the immediate priority is volume and oxygen-carrying capacity.

• AB plasma contains no anti-A or anti-B, so ideally AB red cells are best, but AB Rh-negative is unavailable in the options.

• Using O, Rh-negative (universal donor red cells) is safe because they lack A, B, and Rh(D) antigens, preventing acute hemolytic reactions and Rh sensitization.

• Giving Rh-positive blood (options a, c) could cause anti-D formation in this Rh-negative patient, but O-negative is still preferred over AB-positive when Rh-negative is unavailable in the exact type.

A major crossmatch is the most important compatibility test performed before a transfusion.

It detects whether the recipient’s serum (or plasma) contains antibodies that could react with antigens on the donor’s red blood cells — which could cause hemolytic transfusion reactions.

Incorrect options:

• (a) Donor serum with donor cells → irrelevant (autologous test).

• (c) Donor serum with recipient cells → old minor crossmatch, not major.

• (d) Recipient plasma with their own cells → auto-control, not crossmatch.

The primary purpose of compatibility testing (which includes the antibody screen and crossmatch) is to detect unexpected antibodies in the recipient’s plasma that could react with antigens on the donor’s red blood cells and cause a hemolytic transfusion reaction.

Incorrect options:

• (a) ABO and Rh grouping → part of testing, but not the primary purpose.

• (c) Donor hemoglobin → unrelated to compatibility.

• (d) Platelet function → not evaluated in red cell compatibility testing.

When a patient has multiple antibodies, phenotyping their red cells tells you which antigens they lack.

• If they lack an antigen, they can make an antibody against it.

• If they have the antigen, they cannot make the corresponding alloantibody.
  This helps narrow down the possible specificities of the antibodies identified in their serum.

The antibody screen (indirect antiglobulin test) is performed before the crossmatch to detect unexpected antibodies in the patient’s serum. It uses reagent red cells with known antigens to see if the patient has developed antibodies against common blood group systems (like Kell, Duffy, Kidd). The results determine the extent of crossmatching required.

Incorrect options:

• (b) Identify donor blood group → done during donor processing, not antibody screening.

• (c) Confirm ABO compatibility → done separately by ABO typing and immediate-spin crossmatch.

• (d) Detect Rh status → determined during Rh typing, not antibody screening.

For Fresh Frozen Plasma (FFP), the plasma must be compatible with the recipient’s red cells to avoid antibody reactions. Since plasma contains antibodies against ABO antigens the recipient lacks, the safest donor plasma comes from AB donors (they have no anti-A or anti-B antibodies).
Rh factor is irrelevant for FFP transfusion because Rh antigens are on red cells, not in plasma.

A diversion pouch is used during blood collection to sequester the first 20-40 mL of blood. This portion of the donation is most likely to contain skin plugs and bacteria introduced by the needle, preventing them from entering the primary collection bag and significantly reducing bacterial contamination of platelet products.

• (a) Needle size affects flow rate, not contamination.

• (c) Skin scrub is standard practice, but the diversion pouch is the specific added step for this purpose.

• (d) UV irradiation is not a standard method for bacterial reduction in platelet storage.

The Antihuman Globulin (AHG) reagent, or Coombs’ reagent, contains antibodies that specifically bind to human IgG and/or complement proteins (like C3d). In the crossmatch, it is added to detect IgG antibodies that have bound to donor red cells during the 37°C incubation phase but are not visible as agglutination.

Incorrect options:

• (b) Detect complement in plasma → AHG can detect complement on red cells, not in free plasma.

• (c) Remove unbound antibodies → washing step does that, not AHG.

• (d) Inactivate antibodies → AHG doesn’t inactivate; it detects bound ones.