Background: Anti-C1q antibodies, targeting the complement system component C1q, are majorly linked to autoimmune diseases. However, anti-C1q antibodies could be detected in other conditions. Detecting anti-C1q antibodies can be clinically relevant in assessing and understanding the immune responses in these diverse diseases.

Objectives: This study aimed to assess anti-C1q antibody positivity in different diseases, including autoimmune diseases, infectious diseases and other chronic diseases.

Methods: Anti-C1q antibodies were examined via ELISA (Yahuilong, China) with a normal range of ≤10 U/ml. The assessment was carried out by two experienced laboratory experts.

Results: In the 20,132 samples examined in our hospital, we conducted an analysis of anti-C1q antibodies, identifying 995 participants with positive antibodies and a mean age of 31.3±15.0. The median value of anti-C1q antibodies was 19 (13, 29) U/ml. Notably, 78.8% of the positive samples belonged to systemic lupus erythematosus (SLE), followed by connective tissue diseases (CTD) at 4.3%, skin rash at 2.9%, and a smaller percentage in other categories such as hepatitis B Virus (HBV) infection (2.1%). Additionally, conditions like thrombocytopenia (1.9%), systemic sclerosis (SSC) (1.5%), chronic kidney disease (1.4%), rheumatoid arthritis (RA) (1.3%), and pneumonia (1.2%) exhibited varying degrees of association with positive anti-C1q antibodies. Autoimmune encephalitis, idiopathic inflammatory myopathy (IIM), antiphospholipid syndrome (APS), thyroiditis, osteoarthritis, and primary biliary cirrhosis (PBC) showed lower prevalence. Notably, 106 individuals with C1q levels above 50 IU/ml were observed, predominantly in SLE (75.5%), skin rash (5.7%), and CTD (2.8%), with smaller percentages in HBV infection, Sjögren’s syndrome (SS), RA, SSC, chronic kidney disease, thrombocytopenia, IIM, cryptococcal meningitis and even ankylosing spondylitis (AS).

Conclusion: These findings underscore the diverse prevalence of anti-C1q antibodies across various diseases, with SLE being the most prominent.

REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests: None declared.