C3 and systemic lupus erythematosus: The patient fulfilled European League Against Rheumatism (EULAR) and American College of Rheumatology (ACR) 2019 criteria for SLE with 16 points (FANA = 1:100, inflammatory polyarthritis (6 points), as well as low C3 and C4 (4 points), and increased anti‐ds DNA (6 points)).6