CLS 3311 Advanced Clinical Immunohematology. ABO Discrepancy’s. ABO Discrepancy. Definition: When the results of the forward grouping (patient cells) do not correspond to the results of the reverse grouping (patient serum) or abnormal reactivity is present (i.e. Mixed Field):
Patient B: Weak reaction with patients serum and A1-cells.
Patient C: Additional reaction with patients serum and A1-cells.
Patient D: Missing reactions with patients serum A1-cells
Chimera: Two cell populations
Testing using Serum or plasma suspended Patient RBCs
Potent cold reacting autoagglutinins
Weakened Antigen Expression
Acquired ‘B’ Antigen
Microbial deacetylating enzymes such as E. coli cleave off the N-Acetyl of the Group A N-acetyl-D-galactosamine immunodominant sugar. The remaining D-galactosamine becomes similar enough to the Group B D-galactose immunodominant sugar that it DOES react with reagent anti-B.
Secondary to bowel obstruction or carcinoma of the bowelProblems with The Forward Grouping:
Non specific red cell aggregation
Still has fibrinogen and can cause fibrin formation (rbc’s can be caught up and appears as clumping)
Increased serum proteins (Multiple Myeloma, etc.), infusion of high molecular weight plasma expandersProblems with TheReverse Grouping
Immunodeficient due to therapy or disease
When an ABO Discrepancy is encountered:
Repeat testing using saline suspended and/or washed patient red blood cell’s. Saline Replacement.
From the beginning: re-label tubes, re-drop patient and reagent drops, etc.
Many labs make the patients red blood cell suspension with the patient’s serum/plasma. If the patient has increased plasma proteins it can cause non-specific red cell aggregation.ResolvingABO Discrepancies
Test patient serum with A1 or A2 cells
For suspected subgroups of A
Causes: Age related (>65, infant), immunosuppressed or immunocompromised,
Resolution: Incubate Room Temperature 15-30 minutes and respin.Check Patient history.
Causes: Acquired ‘B’ antigen.
Resolution: Patient history – bowel obstruction, carcinoma of the bowel. (E. coli deacetylation of the Group A antigen.)
Causes: 1)Subgroup of A – A2 with anti-A1. 2) Unexpected cold reacting antibody to antigen on reagent A1 cells.
Resolution:1) Test patient cells with anti-A1 lectin and with patient serum test A2 cells2) Antibody screen should demonstrate unexpected cold reacting antibody.
MF stands for mixed field reaction.