Simultaneous detection of IgG, IgM, IgA complexes and C3d attached to erythrocytes by flow cytometry

Positive direct antiglobulin test in COVID-19 patients: Decision-making process

In this unprecedented crisis of severe acute respiratory syndrome coronavirus 2 and its associated coronavirus disease 2019 (COVID-19), polymerase chain reaction and then serological testing platforms have been massively developed to face the important screening demand. Polymerase chain reaction and serological testing platforms are not the only actors impacted by the crisis, transfusion services are facing important difficulties. A positive direct antiglobulin test is frequently observed for patients encountering COVID-19. Patients with severe symptoms may develop anaemia and become good candidates for blood transfusions. The interpretation of a positive direct antiglobulin test for patients recently transfused and suffering from COVID-19 is complex. The differentiation between COVID-19 induced antibodies and possible associated transfusion alloantibodies is therefore crucial. In this context, the elution technique incorporated in an appropriate decision-making process plays its full role. This intricate topic is presented through a case report followed by literature review and finally decision-making process for COVID-19 patients necessitating red blood cells administration.

Utilisation of Flow-cytometry in the Diagnosis of Auto Immune Haemolytic Anaemia

Auto Immune Haemolytic Anaemia (AIHA) is one of the most common types of acquired haemolytic anaemias. Its main cause is auto-antibody mediated rapid destruction of Red Blood Cells (RBCs). Demonstration of a positive Direct Antiglobulin Test also known as Coomb's test, against these autoantibodies is the crucial serological assay in the diagnosis of AIHA. This routinely used test has the disadvantage of low sensitivity and does not detect low levels of red cell auto antibodies leading to false negative results sometimes. Flow cytometry can effectively diagnose such patients with low levels of autoantibodies. This study was carried out in a tertiary care center, where patients with suspected AIHA were studied during 2 years period. Blood samples of suspected patients of AIHA were tested by both Gel Card Test and by Flow-cytometry for detection of RBC bound IgG. A total of 50 patients with suspected diagnosis of AIHA were studied by flow-cytometry as well as by Gel card test for detection of RBC bound IgG. Out of these 50 cases, 41 cases have turned out to be positive and 9 were negative by flow-cytometry. By Gel card test, out of 50 cases, 34 were positive and 16 were negative. Therefore, there were 7 cases which were negative for RBC bound IgG by Gel card test and these were positive by flow-cytometry. Flow-cytometry is a reliable and more sensitive method and can be used as a new routine diagnostic technique for AIHA.

The Direct Antiglobulin Test: Indications, Interpretation, and Pitfalls

The direct antiglobulin test (DAT; sometimes referred to as the "Coombs" test) continues to be one of the most widely used assays in laboratory medicine. First described about 70 years ago, it is elegantly simple in design, yet it is widely complex in its applications and interpretations, and it is prone to false-positive and false-negative results. The overall objective of our review is to provide practicing pathologists with a guide to identify situations when the DAT is useful and to highlight disease-specific shortcomings as well as general pitfalls of the test. To accomplish these goals, this review will discuss the following: (1) the history of the DAT, (2) how the test is performed in the clinical laboratory, (3) clinical situations for its use, (4) its interpretation, and (5) the pitfalls associated with DAT assays, including causes of false positivity.

Delivery route determines the presence of immune complexes on umbilical cord erythrocytes

OBJECTIVE

Umbilical cord blood offers a unique opportunity to study the basal level of immunoglobulin complexes. This study aims to determine the presence of immune complexes and complement deposition on erythrocytes from umbilical cord blood from normal, full-term pregnancies.

METHODS

In vitro pre-formed IgA, IgG, and IgM complexes were used as positive control for flow cytometry detection, and for C3d deposition. Blood samples (34) of umbilical cord blood taken from vaginal and cesarean deliveries were tested for the presence of immunoglobulin complexes.

RESULTS

Fourteen samples from vaginal deliveries and 20 samples from cesarean deliveries were assessed. IgG and IgM complexes were detected on erythrocytes, whereas no IgA complexes or complement deposition was observed. Interestingly, the percentage of IgG complexes was higher on erythrocytes from vaginal delivery samples compared to those from cesarean deliveries. No other associations between immune complexes and other maternal or newborn variables were found.

CONCLUSIONS

IgG and IgM complexes seem to be normally present on umbilical cord erythrocytes. Erythrocytes from vaginal deliveries have a higher percentage of IgG complexes present compared to that from cesarean deliveries. Since no C3d activity was detected, these complexes are non-pathological and should be part of the newborn's initial innate immune response.

Complement deposition in autoimmune hemolytic anemia is a footprint for difficult-to-detect IgM autoantibodies

In autoimmune hemolytic anemia autoantibodies against erythrocytes lead to increased clearance of the erythrocytes, which in turn results in a potentially fatal hemolytic anemia. Depending on whether IgG or IgM antibodies are involved, response to therapy is different. Proper identification of the isotype of the anti-erythrocyte autoantibodies is, therefore, crucial. However, detection of IgM autoantibodies can be challenging. We, therefore, set out to improve the detection of anti-erythrocyte IgM. Direct detection using a flow cytometry-based approach did not yield satisfactory improvements. Next, we analyzed whether the presence of complement C3 on a patient's erythrocytes could be used for indirect detection of anti-erythrocyte IgM. To this end, we fractionated patients' sera by size exclusion chromatography and tested which fractions yielded complement deposition on erythrocytes. Strikingly, we found that all patients with C3 on their erythrocytes according to standard diagnostic tests had an IgM anti-erythrocyte component that could activate complement, even if no such autoantibody had been detected with any other test. This also included all tested patients with only IgG and C3 on their erythrocytes, who would previously have been classified as having an IgG-only mediated autoimmune hemolytic anemia. Depleting patients' sera of either IgG or IgM and testing the remaining complement activation confirmed this result. In conclusion, complement activation in autoimmune hemolytic anemia is mostly IgM-mediated and the presence of covalent C3 on patients' erythrocytes can be taken as a footprint of the presence of anti-erythrocyte IgM. Based on this finding, we propose a diagnostic workflow that will aid in choosing the optimal treatment strategy.