Hello @adah, welcome to Connect. I have no medical training or background but have read that if your immune system makes low levels of antibodies, you may have a greater chance of developing repeated infections. There are some good explanations of the tests here:

University of Michigan - Immunoglobulins: Test Overview
-- https://www.uofmhealth.org/health-library/hw41342

Blood Tests Explained: Immunoglobulins (PDF)
-- https://www.iwmf.com/sites/default/files/docs/bloodcharts_ig.pdf