In the immunology items, positive anti-DNA antibodies, antiphospholipid antibodies, and direct Coombs’ tests were more prevalent, and the total scores were significantly higher in the SLE group with low C3 and C4 than in the SLE group with low C3 or C4 levels in all three classification criteria, SLICC-2012, EULAR/ACR-2019, and SLERPI. Here, C3 is linked to systemic lupus erythematosus.