Clinical parameters significantly associated with < or >553.5 IU/mL anti-RBD IgG were the diagnosis of a monoclonal gammopathy (P = 0.03), treatment status (P < 0.001), number of prior lines of therapy (P = 0.003), and anti-CD38 therapy (P = 0.03). The gene discussed is CD38; the disease is monoclonal gammopathy.