Factors associated with serum IgM concentrations: a general adult population study

Background and aim To investigate the influence of common factors on serum immunoglobulin M (IgM) concentrations in adults, and clinical associations with high and low values. Methods We measured serum IgM levels using immunonephelometry in a random sample of 1510 individuals (aged 18-91 years, 44.7% male). We obtained data defining metabolic syndrome from all participants, defined atopy by skin prick tests to aeroallergens, and assessed lifestyle factors by questionnaire. Results Women showed higher IgM concentrations than men; 95 (6.3%, mostly male) individuals showed low (<0.40 g/L) IgM values, and 64 (4.2%, mostly female) showed high (>2.30 g/L) IgM values. Individuals with abnormal IgM concentrations had no history of opportunistic infections nor a different atopy prevalence. Serum IgM concentrations decreased with age, and obesity was negatively associated with IgM concentrations. Alcohol consumption, smoking, physical activity, and metabolic syndrome had no significant influence in the multivariate analyses. Conclusions Many adults in the general population show abnormally high or low IgM concentrations with no evidence of immunodeficiency-associated diseases. Sex and age should be considered when defining reference IgM concentrations.