HP_0004315 (Decreased circulating IgG concentration) is an abnormally decreased level of immunoglobulin G (IgG) in blood. Also known as: Decreased IgG level, Decreased IgG level in blood, Decreased circulating IgG level, Decreased gamma-globin expression, Decreased immunoglobulin G, Decreased serum IgG, IgG deficiency, Reduced IgG levels.