Previous investigations of the relationship between characteristics of immunoproteins on red blood cells (RBCs) and the occurrence of autoimmune haemolysis yielded divergent results. Here, we studied these characteristics in autoimmune haemolytic anaemias (AIHAs) to determine their relationship with the degree of anaemia at diagnosis. We studied at diagnosis 52 cases of warm AIHA with positive direct antiglobulin test. Immunohaematological testing and determination of immunoglobulin class, complement, and immunoglobulin G (IgG) were performed using gel technology (GCT). Median haemoglobin (Hb) levels significantly differed between cases with IgG1 only or negative for IgG subclasses (7.4 g/dl), those with IgG3 or IgG1 + IgG3 (6.5 g/dl), and those with multiple immunoglobulins (5 g/dl). Logistic regression indicated that IgG3 detection was the only variable significantly related to the occurrence of RBC transfusion in AIHA (odds ratio 4.05, 95 % CI 1.1-14.7). In our study, the type of immunoprotein(s) on the RBC surface was associated with different Hb levels at AIHA diagnosis. IgG3 and multiple immunoglobulins were associated with lower Hb levels; IgG3 was also associated with a higher percentage of patient transfusions in the first week after diagnosis. Thus, qualitative differences in these immunoproteins may lead to deeper and more prolonged anaemia levels, influencing the need for RBC transfusion.