Regarding the EULAR/ACR-2019 criteria, statistically significant associations were found between meeting the EULAR/ACR-2019 classification criteria and the presence of low C3 and C4 (p = 0.03), anti-dsDNA (p < 0.01), lupus nephritis III-IV (p < 0.05) and arthritis (p < 0.01). The gene discussed is C3; the disease is Arthritis.