Interesting case. I assume B12 was normal, but given the degree of macrocytosis, please confirm that B12 +/- serum methylmalonic acid were in fact checked, as severe B12 deficiency leading to ineffective erythropoeisis can mimick hemolytic anemia which is necessary to rule out (although less likely given adequate RI). With that ruled out, this would be consistent with warm AIHA, with first line rx being 1-2 mg/kg prednisone for around 2 weeks followed by a slow taper >1 month after. If that is ineffective or the patient relapses or unable to wean off steroids, then you are correct, adding rituxan is generally what the next step would be in most cases. However, this case is a little unique in that there is a clonal plasma cell population peripherally & in marrow, and the clonal plasma cells may actually be the direct cause of the wAIHA here. If that is the case, then rituximab may not be effective here as it may be the plasma cells and not the B-cells producing the pathogenic antibody. Unfortunately there is no great way to distinguish that I know of. I am happy to reconsult on the case once a steroid trial has been done should it not work or the patient relapses, but generally steroids are >80% effective in wAIHA.