Routine Tests

We start by identifying the patient’s fundamental blood type (ABO/Rh). Then, we screen their plasma for unexpected “weapons” (Antibody Screen). If we find any, we identify them and assess their danger level (Antibody ID/Significance). Before any transfusion, we do a final check between the patient and the specific donor unit (Crossmatch). Separately, if we suspect red cells are already being attacked in vivo, we perform a DAT

Each step builds on the last, creating a robust safety system. Keep practicing these concepts – they are the heart of safe transfusion practice!

Blood Grouping Tests (ABO/Rh)

• The Goal: Establish the patient’s (and donor’s) identity in the two most critical blood group systems
• What We Do
  • ABO: Determine the ABO group (A, B, AB, or O). We do this two ways, and they MUST match:
    • Forward Type: Testing the patient’s Red Cells with known Anti-A and Anti-B reagents to see which antigens (A or B) are present
    • Reverse Type: Testing the patient’s Plasma/Serum with known A1 and B Red Cells to see which expected antibodies (Anti-A or Anti-B) are present (Landsteiner’s Rule!)
  • Rh(D): Determine if the D antigen is present (+) or absent (-) on the patient’s Red Cells using Anti-D reagent. Includes Weak D testing (an IAT procedure) if the initial D test is negative, especially crucial for donors and sometimes newborns
• Why It Matters: ABO incompatibility can cause rapid, severe intravascular hemolysis – potentially fatal. Rh(D) is highly immunogenic, and giving Rh(D)+ blood to an Rh(D)- person can easily stimulate anti-D production, causing issues with future transfusions or pregnancies (HDFN)

Compatibility Tests (Antibody Screen & Crossmatch)

• The Goal: Ensure the patient’s plasma won’t attack the donor red cells we plan to transfuse. This is our pre-transfusion safety check
• What We Do
  • Antibody Screen (Detection): A broad search using the patient’s Plasma/Serum against Screening Cells (Group O cells with a known profile of common, clinically significant antigens). We’re looking for unexpected antibodies (beyond anti-A/anti-B). Usually performed using the Indirect Antiglobulin Test (IAT) principle (incubate at 37°C, wash, add AHG)
    • Negative Screen: Generally means no common antibodies detected
    • Positive Screen: An antibody is likely present; requires further investigation (Antibody ID)
  • Crossmatch: The final check. Mixes patient Plasma/Serum directly with red cells from the specific Donor Unit selected
    • Types: Can be Immediate Spin (IS - primarily ABO check), Antiglobulin (AHG - full IAT if antibodies are known/suspected), or Electronic (computer verification under strict criteria if screen is negative and other rules met)
    • Result: Compatible = Okay to transfuse. Incompatible = STOP, investigate!
• Why It Matters: Detects antibodies that could cause a hemolytic transfusion reaction. The crossmatch is the ultimate confirmation of ABO compatibility and detects patient antibodies reactive against the specific donor cells

Antibody Identification & Clinical Significance

• The Goal: If the Antibody Screen is positive, we need to figure out exactly which antibody(ies) is/are present and whether they are likely to cause problems
• What We Do
  • Identification: Test patient Plasma/Serum against a larger Panel of reagent red cells with extensive, known antigen profiles. By matching the pattern of reactivity (positive and negative reactions) with the antigen profiles (using the “rule-out” method), we determine the antibody’s specificity (e.g., anti-K, anti-Fya). May involve special techniques (enzymes, adsorption). An Autocontrol (patient plasma vs patient cells) helps distinguish allo- vs. autoantibodies
  • Clinical Significance: Assess if the identified antibody is capable of causing HTRs or HDFN. Key factors: Is it IgG? Does it react at 37°C? Is it known to cause hemolysis (e.g., Rh, Kell, Duffy, Kidd antibodies are usually significant; Lewis, P1, M often aren’t)?
• Why It Matters: Identification is essential to select antigen-negative blood for transfusion. Assessing significance determines if this special selection is necessary

Direct Antiglobulin Test (DAT)

• The Goal: Determine if the patient’s red blood cells are coated with immunoglobulin (IgG) or complement components in vivo (inside their body right now)
• What We Do: Take patient WASHED Red Blood Cells and directly add Anti-Human Globulin (AHG) reagent (initially Polyspecific, then Monospecific anti-IgG and anti-C3d if positive). Agglutination indicates the cells were coated before the blood was drawn
• Why It Matters: This is NOT typically part of routine pre-transfusion testing but is crucial for investigating:
  • Hemolytic Transfusion Reactions (HTRs)
  • Hemolytic Disease of the Fetus and Newborn (HDFN)
  • Autoimmune Hemolytic Anemias (AIHA)
  • Drug-Induced Hemolytic Anemias (DIHA) A positive DAT signals that something (antibody/complement) is attached to the red cells in the patient’s circulation