The serum level of IgM antibodies against Glc(alpha1,4)Glc(alpha) (GAGA4) is higher in relapsing remitting multiple sclerosis (RRMS) compared to other neurological disease (OND) patients and healthy controls (HC). Detecting the level of anti-GAGA4 antibody by enzyme immunoassay and total IgM, we confirmed that anti-GAGA4 IgM can differentiate RRMS from OND patients and HC. Moreover, secondary progressive MS (SPMS) and RRMS patients have similar levels of anti-GAGA4 demonstrating the biomarker's presence throughout the disease. Interestingly, the anti-GAGA4 assay may also differentiate between primary progressive MS (PPMS) and RRMS/SPMS patients, since nearly all PPMS patients were negative for the assay.