If my serum IgA levels are low, does that mean my secretory IgA levels are low, too?

No. Levels of serum IgA levels do not necessarily predict or determine mucosal secretory IgA – and vice versa. In serum, IgA is the second most abundant antibody after IgG. Secretory IgA (SIgA) is produced from two IgA molecules. However, adequate IgA is not the only factor impacting SIgA production. Stress is just one example of a negative impact on low SIgA.