What is red antibody (Red Cell Antibody) screening?

Red Blood Cell Antibody Screening

Red blood cell (RBC) antibody screening is a laboratory test that detects the presence of unexpected antibodies in a patient's serum or plasma that could react against antigens on transfused red blood cells, potentially causing hemolytic transfusion reactions.

Purpose and Clinical Significance

RBC antibody screening is a critical pretransfusion safety test performed to:

• Identify patients who have developed alloantibodies against red cell antigens from previous transfusions, pregnancy, or transplantation 1
• Prevent acute and delayed hemolytic transfusion reactions (HTRs) by detecting incompatible antibodies before transfusion 1
• Guide selection of antigen-negative donor units when antibodies are detected, particularly for patients requiring chronic transfusion therapy 1

Testing Methodology

The antibody screen uses standardized reagent red blood cells with known antigen profiles:

• Screening typically employs 2-3 reagent red cell samples that collectively express the most clinically significant blood group antigens 2, 3
• Column agglutination technology (CAT) using gel cards or glass bead systems are the most widely used modern methods, offering high sensitivity and specificity (>99%) 2, 3, 4
• The gel test uses microtubes filled with gel and antiglobulin reagent, where agglutinated cells are trapped in the gel during centrifugation while non-reactive cells pass through 4
• Testing includes both immediate spin and antiglobulin phases to detect IgM and IgG antibodies 2, 3

Clinical Applications

Pretransfusion Testing

All patients should undergo antibody screening before receiving red cell transfusions 1. When the screen is positive:

• Antibody identification panels (typically 11-cell panels) are used to determine the specific antibody present 1, 2, 5
• Antigen-negative blood must be selected to prevent hemolytic reactions 1
• Extended red cell antigen profiling of the patient expedites antibody identification and compatible unit selection 1

Special Populations

For patients with sickle cell disease (SCD), prophylactic extended antigen matching for Rh (C, E or C/c, E/e) and K antigens is strongly recommended to prevent alloimmunization 1. This population has the highest alloimmunization rates of any transfused patient group 1.

Serial antibody screening within 3 months is suggested for patients who experience delayed hemolytic transfusion reactions without identified antibody specificity, as the antibody may become detectable weeks to months later 1.

Pregnancy Screening

Antibody screening is essential in pregnant women to:

• Detect antibodies that could cause hemolytic disease of the fetus and newborn 1
• Allow early intervention with maternal treatment or fetal monitoring when clinically significant antibodies are identified 1

Important Caveats

• Recent transfusion can interfere with patient phenotyping but not with antibody screening itself 1
• Weak or enzyme-only reactive antibodies may be missed depending on the methodology used, with gel card systems generally detecting more weak antibodies in stored samples 2
• Antibodies can become undetectable over time (evanescence) but may cause delayed hemolytic reactions upon re-exposure 1
• A negative antibody screen does not guarantee absence of all clinically significant antibodies, particularly rare specificities not represented on screening cells 2