Red Blood Cell Antigen Genotyping

Red blood cell (RBC) antigen testing is useful in determining allelic variants that predict RBC antigen phenotypes for patients with recent history of transfusion or with conflicting serologic antibody results due to partial, variant, or weak expression antigens. It is also useful as an aid in management of hemolytic disease of the fetus and newborn (HDFN); for additional information on HDFN testing, refer to the ARUP Consult Hemolytic Disease of the Fetus and Newborn topic.

Prevalence and/or Incidence

Erythrocyte alloimmunization occurs in up to 58% of patients with sickle cell, up to 35% in other patients who are transfusion-dependent, and in approximately 0.8% of all individuals who are pregnant.

Symptoms

Transfusion reactions or HDFN can occur due to alloimmunization:

• Intravascular hemolysis: hemoglobinuria, jaundice, shock
• Extravascular hemolysis: fever and chills
• HDFN: fetal hemolytic anemia, hepatosplenomegaly, jaundice, erythroblastosis, neurologic damage, hydrops fetalis

Clinical presentation is variable and dependent upon the specific antibody and recipient factors.

Pathophysiology

Extravascular Hemolysis

Removal of antibody-bound RBCs via splenic macrophages

Intravascular Hemolysis

• Rare for non-ABO antibodies
• Donor RBCs are destroyed by the recipient's antibodies while they are still inside blood vessels.
• Hemoglobin released into plasma and excreted in urine; bilirubin accumulates in blood

HDN-Mediated Disease

• Caused by antigen-antibody mediated red-cell hemolysis from previously transferred maternal antibodies
• Examples of antibodies associated with HDFN:
  • Rh (Ant-D, -C, -c, -E, and -e)
  • Kell (Anti-K, -k, -Kp^a, -Kp^b, -Js^a and -Js^b)
  • Duffy (Anti-Fy^a and -Fy^b)
  • MNS (Anti-M, -N, -S, -s, and -U)
  • Kidd (Anti-Jk^a and -Jk^b)
• Anti-D is the most common cause of HDFN, followed by anti-c, anti-K, and anti-E; anti-Jk^a and -Jk^b are rare causes
• Antibodies cross the placenta and cause immune destruction of RBCs in fetus and leads to hydrops fetalis.

Genetics

Refer to the Genes and Variants Tested table below.

Inheritance

Typically codominant for RBC antigens; autosomal recessive for HbS

Sensitivity/Specificity

• Clinical sensitivity and specificity:
  • >99% for C, c, E, e, K, k, Jk^a, Jk^b, Fy^a, Fy^b, M, N, S, s
  • Unknown for Kp^a, Kp^b, Js^a, Js^b, Lu^a, Lu^b, Di^a, Di^b, Co^a, Co^b, Do^a, Do^b, Jo^a, Hy, LW^a, LW^b, Sc1, Sc2, U, V, VS, HbS
• Analytic sensitivity and specificity:
  • >99% for C, c, E, e, K, k, Jk^a, Jk^b, Fy^a, Fy^b, M, N, S, s
  • Unknown for Kp^a, Kp^b, Js^a, Js^b, Lu^a, Lu^b, Di^a, Di^b, Co^a, Co^b, Do^a, Do^b, Jo^a, Hy, LW^a, LW^b, Sc1, Sc2, U, V, VS, HbS

Results

• Predicted phenotype for each RBC antigen tested will be provided
  • If identified, weak alleles will be reported.
• Possible variant
  • Reported for allele combinations that have not widely been reported in the literature
• Indeterminate
  • Abnormal signal intensities may result in the inability to predict genotype resulting in indeterminate results for all tested antigens and HbS.

Limitations

• Only the variants listed will be interrogated.
• Does not test for Rh D, a major cause of HDFN
• Patients who have had allogeneic hematopoietic stem cell transplants may have inconclusive results.
• Diagnostic/phenotype prediction errors can occur due to:
  • Rare variants affecting primer/probe binding
  • Molecular events that affect the blood-group antigen expression and phenotypes that are not detected by this assay (i.e., certain null phenotypes or other phenotypes with altered expression)
• This assay is not designed to diagnose sickle cell disease.