The relation between C-reactive protein and serum amyloid A in patients with autoinflammatory diseases

• Published in: Pediatric rheumatology online journal Vol. 20; no. 1; p. 106
• Main Authors: Legger, G E, Dermer, C W E, Brunger, A F, van Daele, P L A, Nienhuis, H L A
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 24-11-2022; BioMed Central; BMC
• Subjects: Acute-phase proteins; Amyloidosis; Blood; C-reactive protein; C-Reactive Protein - metabolism; Care and treatment; Familial Mediterranean fever; Hereditary autoinflammatory diseases; Hereditary Autoinflammatory Diseases - diagnosis; Humans; Inflammation; Medical examination; Proteins; Retrospective Studies; Serum Amyloid A Protein - analysis; Serum Amyloid A Protein - metabolism; C-reactive protein; Acute-phase proteins; Hereditary autoinflammatory diseases; Amyloidosis; Familial Mediterranean fever; Inflammation; Serum amyloid A protein
• DOI: 10.1186/s12969-022-00757-9
• EISSN: 1546-0096

Autoinflammatory diseases are rare disorders of the innate immune system characterized by fever and other signs of inflammation. A feared complication of autoinflammatory diseases is the development of AA amyloidosis. AA amyloidosis is caused by extracellular deposition of soluble serum amyloid A (SAA) proteins as insoluble amyloid fibrils leading to organ damage. Prolonged high levels of SAA are a prerequisite to develop AA amyloidosis. Since measurement of SAA is relatively expensive and sometimes unavailable, C-reactive protein (CRP) is often used as a surrogacy marker to test for inflammation.
The aim of this research is to evaluate the possible relation between CRP and SAA.
A retrospective cohort of patients with autoinflammatory diseases (n = 99) where SAA and CRP blood testing was performed in the period between 2015 and 2021 in the University Medical Centre in Groningen was used to investigate the correlation between CRP and SAA.
CRP and SAA have a high correlation (rho = 0.755, p < 0.001). A CRP value below 0.45 mg/L results in 100% sensitivity for SAA below 4 mg/L. CRP below 5 mg/L is a good predictor of SAA below 4 mg/L with 85.4% sensitivity and 83.6% specificity. Only prednisone and erythrocyte sedimentation rate (ESR) significantly influence the relation between CRP and log
SAA.
There was a significant correlation between CRP and SAA in our retrospective cohort. CRP levels below 5 mg/L proved to be highly predictive of SAA levels below 4 mg/L. This may not be true for patients on steroids.