What does it mean that I have a low IgM level?

Low IgM. Low IgM levels in and of themselves are not common, but can occur. If they occur with low IgG levels or with other clinical symptoms the diagnosis can be different. Isolated low IgM can be caused by a variety of factors, and often eventually resolves. See an immunologist for further evaluation to determine the cause.
? immune deficiency. Igm is the first antibody made as infections begin; in the circulation, 5 antibodies are usually connected together and when activated, they do a particularly good job at announcing an early infection. Low IgM by itself is rarely seen; when other antibodies (igg, iga) are also low, it could mean an immune deficiency of some kind. Consulting an immunologist can help in determining the cause.