Anti-Citrullinated Protein Antibody (ACPA)

Related Subjects: | Ferritin | CEA | ESR | CRP | ALP | LDH | HbA1c | Alpha Fetoprotein | Anti-Hu ab | Biochemical Lab values

ACPAs precede the onset of clinical RA and are associated with more severe disease, making them useful as diagnostic and prognostic tools.

About

• Turnaround time may be several weeks
• Anti-Citrullinated Protein Antibodies

Aetiology

• More than 90% of Rheumatoid arthritis patients have autoantibodies that recognise proteins in which arginine residues have been modified to citrulline. This process may well be the cause of the inflammatory process since citrullinated proteins and the enzymes responsible for producing them are found in inflamed synovium.
• These antibodies are detected in the laboratory using artificial cyclic citrulline peptides (anti-CCP Ab). This assay is far more sensitive and specific than rheumatoid factor for the diagnosis of rheumatoid arthritis and some childhood arthritides. However, the 2009 NICE guidelines (bizarrely) recommend the continued use of rheumatoid factor based on cost-effectiveness.
• More sensitive and more specific than rheumatoid factor for diagnosis of rheumatoid arthritis and some juvenile arthritides.
• Positive anti-CCP in adults is almost certainly associated with rheumatoid arthritis though the autoantibody can appear before clear clinical signs. A small minority of RA patients do not have anti-CCP antibodies though with the development of each new generation of the test, this number falls.

Clinical

• Suspected RA

Investigations

• Fluorescence enzyme linked immunoassay (Phadia Immunocap 250): Synthetic citrullinated peptides second generation: IgG antibodies.
• Negative = <7U/mL
• Equivocal = 7-10U/mL
• Positive = >10U/mL
• Assay Range 0.4 to >340U/ml

References