Antibody Detection Identification

• There are several types of antibodies present in the blood, but naturally occurring anti-A and anti-B are the only red cell antibodies that are regularly found in normal plasma or serum

  all others are unexpected red cell antibodies
• two types of unexpected antibodies are autoantibodies and alloantibodies
• alloantibodies react only with allogenic cells that express the corresponding antigen
• alloantibodies: when an individual produces an antibody to an antigen they lack (from the same species)
• autoantibodies: when an individual produces an antibody to an antigen they posess
• autoantibodies react with red cells of the antibody producer
• autoantibodies also usually react with most reagent red cells as well as with the autologous red cells (the autocontrol)
• alloantibodies

  • immunization to a red cell antigen may result from transfusion, pregnancy, transplantation, injections of immunogenic material
• alloantibodies: if you have no specific immunizing event that the antibodies are presumed to have resulted from exposure to environmental, bacterial, or viral antigens that are similar to blood group antigens
• about 0.5-1.5% of the general population have alloantibodies
• alloantibody detection

  • alloantibodies can be detected in many ways:
  • an ABO test
  • an antibody detection test
  • compatibility test
  • in an eluate prepared from red cells coated with an alloantibody
• • alloantibodies can be detected in many ways:
  • an ABO test (e.g. mismatch between forward and reverse)
• after an alloantibody is detected, it's specificity should be determined, and its clinical significance assessed
• a clinically significant red cell antibody is defined as an antibody that is frequently associated with

  • HDFN
  • HTR
  • a noticeable decrease of transfused red cells survival
• the degree of clinical significance varies among the antibodies:

  • some cause destruction of incompatible red cells within hours or minutes
• the degree of clinical significance varies among the antibodies:

  • others decrease red cell survival by only a few days
• the degree of clinical significance varies among the antibodies:

  • still others cause no discernable shortened red cell survival
• the degree of clinical significance varies among the antibodies:

  • some antibodies cause HDFN whereas others may cause a positive DAT (direct antiglobulin test) in the fetus without clinical evidence of HDFN
• alloantibody significance

  • preanalytical considerations:
  • check previous patient medical history including prior transfusions and pregnancy
  • it's very uncommon to produce clinically significant alloantibodies without prior immunization through pregnancy or transfusion
• if previously transfused, it is critical to know when the most recent transfusion was given
• in general, women are more likely to have alloantibodies than men
• infants less than 6 months usually do not produce antibodies, but newborns may have antibodies of maternal origin
• if transfusion is very recent, then we may not catch antibody in pretransfusion testing
• antibodies and disease

  • certain diseases have been associated with red cells antibodies, depending on method used, can be detected and identified
• antibodies and disease

  • warm autoantibodies often accompany diagnosis such as warm autoimmune hemolytic anemia (WAIHA), systemic lupus erythematosus (SLE), multiple myeloma, chronic lymphocytic leukemia, and lymphoma
• WAIHA - may see hemolysis instead of agglutination
• antibodies and disease

  • try to rule out alloantibodies, might be difficult with autoantibody present
  • sometimes just give "least incompatible blood"
• cold antibodies

  • cold agglutinin disease (CAD) - anti-I
• cold antibodies

  • Reynaud's phenomenon - anti-I
• cold antibodies

  • infections with Mycoplasma pneumoniae - anti-I
• cold antibodies

  • infectious mononucleosis - anti-i
• cold antibodies

  • Paroxysmal cold hemoglobinuria (PCH) - associated with syphilis in adults and viral infections in children (anti-P)
• Drugs and antibodies

  • some drugs can cause antibody identification problems including
  • intravenous immunoglobulin (IVIG) and Rh immune globulin (RhIG, RhoGAM)
  • intravenous RhIG
• intravenous immunoglobulin (IVIG) and Rh immune globulin in antenatal and postnatal patients
• one dose of RhoGAM (anti-D) covers a 30 mL bleeding, meaning 30 mLs of baby Rh+ cells have mixed with the mom's blood. if the bleed was actually less than 30 mLs, there could be anti-D floating around
• intravenous RhIG - used to treat thrombocytopenia and could explaint he presence of anti-D in Rh+ patient
• RhIG: a combo of anti-D plus other antibodies are given to Rh+ individuals with immune-thrombocytopenia; the idea is the coated red cells are phagocytized by the spleen, which is then too overwhelmed to bother phagocytizing the platelets; must watch for decreased hematocrit
• detection of alloantibodies

  • serum or plasma can be used for antibody detection and identification
  • screening cells are made from group O red cells and offered as sets of two or three
• Detection of alloantibodies

  • reagent cells licensed by the FDA must express the following antigens: D, C, E, c, e, M, N, S, s, P1, Lea, Leb, K, k, Fya, Fyb, Jka, and Jkb (18)
• Detection of alloantibodies

  • the three cell sets usually are presumed to be from homozygous donors with double dose expression for the following common antigens: D, C, E, c, e, M, N, S, s, Fya, Fyb, Jka, and Jkb (13)