Abstract
IgG-coated RBCs are routinely used to confirm appropriate procedures when negative hemagglutination occurrs in the indirect antiglobulin test (IAT). We undertook this study after encountering a case of agglutination failure of IgG-coated RBCs by polyethyleneglycol (PEG)-IAT in a patient with hyperglobulinemia.
We investigated whether IgG-coated RBCs could be agglutinated by anti-IgG using the PEG-IAT technique after incubation with 143 sera, in which no irregular anti-red cell antibodies were present, from patients with hyperglobulinemia.
Failure of agglutination (false negative reaction) was found more frequently (p<0.001) with the original PEG-IAT (4 drops in test mixture) (46/143 sera; 32%) than the modified PEG-IAT (2 drops) (15/143 sera; 11%). The rate of residual-IgG in the supernatant in the mixture of PEG and patient's serum was significantly (p<0.01) higher with the modified than the original method, at 14.4% vs. 3.0% in hyperglobulinemia patients and 28.5% vs. 5.7% in healthy controls.
The addition of anti-D alloantibody (final titer 1:4) in 3, 000-5, 000mg/dL of immunoglobulin concentration revealed that PEG could cause false-negative IAT results due to the neutralization of anti-IgG through precipitation of immunoglobulins in testing tubes.
Albumin-IAT, low ionic strength solution-IAT or saline-IAT may assist in resolving interference by PEG in cases of hyperglobulinemia.
