C3 and systemic lupus erythematosus: Regarding autoantibodies and disease activity indicators, compared with patients with SLE without thrombocytopenia, patients with SLE with thrombocytopenia had a lower positivity rate for anti‐Ro60 and anti‐Ro52, lower C3 and C4 levels, and higher SLEDAI 2000 scores, even when the thrombocytopenia score was excluded from the SLEDAI 2000 score, suggesting that patients with SLE with thrombocytopenia had higher disease activity compared with patients with SLE without thrombocytopenia.