Background and objectives: Commercially available gel test microtubes are not available with antisera for the determination of IgG subclasses. The aim of this study was to adapt the gel technique for this purpose and apply it to the investigation of patients with autoimmune haemolytic anaemia (AIHA).
Materials and methods: We studied 66 red cell samples from 49 patients with AIHA of the warm-active IgG type. Standard serologic and haematologic methods were used. We adapted the DiaMed gel test by using IgG-subclass antisera.
Results: We found the adapted test useful in determining the subclass of autoantibodies in eluates. We could identify the IgG subclass in all the AIHA patients, even those that were 'Coombs-negative', with less than 200 IgG molecules bound in vivo per red cell. Comparison of the gel test with the standard spin tube test and the microtiter plate test showed the superiority of the gel test, i.e., detection of IgG subclasses was much better than with the tube test and the results were more clearcut than those of the microplate test. The gel test is also the simplest and least time-consuming and permits a later reading of results. Application of the test in our 66 samples confirmed that IgG1 was the most frequent (96%). In 59% of the cases it was accompanied by IgG of other subclasses. Multiple subclasses were most common in the cases with stronger in vivo IgG red cell sensitization and severe haemolysis. Accompanying IgG3 was detected only in patients with obvious haemolysis.
Conclusion: The gel test is more sensitive than other procedures for the determination of IgG subclass and has the advantages of simplicity, rapidity, low cost, and stability of the agglutinates.