The immunologist was consulted, and the patient was diagnosed with SLE, based on the following EULAR classification criteria: fever, arthralgia, leucopenia, positive ANA HEp2, positive anti-dsDNA and anti-Sm antibodies, proteinuria, low C3 and C4 complement, and positive antiphospholipid antibodies. Here, C4A is linked to systemic lupus erythematosus.