Can C-reactive protein be used as a surrogate marker of IL-6 in a broad array of clinical entities?

Background: C-reactive protein (CRP) is commonly performed, whereas cytokine testing is limited to research. Aims: To determine CRP correlation to cytokines IL-6, IL-1ß and TNF-α. Results: Consecutive samples (n = 307) were collected over 24 h. Ninety-six patients (31%) had acute infections, and 23 patients (7.5%) had autoimmune or inflammatory disease presentations. A strong correlation between CRP and two IL-6 assays (r = 0.74 and r = 0.71; p < 0.001) was present. CRP did not correlate with IL-1ß and TNF-α across the data set. Bacterial infection had a significantly higher CRP and IL-6 (p < 0.001), while only CRP was elevated in inflammatory and autoimmune diseases (p < 0.001). Discussion: CRP may be used as a surrogate marker of IL-6 levels in the routine diagnostic laboratories.

Immunoglobulin G4 related disease: a single-centre experience from South Australia.

BACKGROUND: IgG4 related disease (IgG4RD) is a newly described multisystem fibro-inflammatory disorder. There is a paucity of literature describing the Australian experience of this rare condition. AIMS: To characterise the Royal Adelaide Hospital IgG4RD cohort with biopsy-proven disease. METHODS: A search of the Frome Road SA Pathology database was performed for all tissue biopsies containing the phrase 'IgG4 positive'. Case notes were reviewed for clinical details, laboratory and radiology results. Histological features according to the Boston Criteria were used. Patients with available case notes, highly suggestive or probable histology and clinical features to suggest IgG4RD were included. RESULTS: Twenty patients had definite or probable IgG4RD and suggestive clinical features; median age 59 (20-76), male : female 1.5:1. There was considerable delay in diagnosis (median diagnosis at 64 months). Organ involvement included: 11 exocrine gland, seven pancreatobiliary, seven nodal, seven soft tissue, five retro-orbital, three retroperitoneal fibrosis and two renal. Systemic symptoms at diagnosis were seen in eight patients. Seven (35%) had an elevated serum IgG4 (>1.35 g/L) at diagnosis. Only 12 (60%) required immunosuppressive treatment (corticosteroids); of these, four (20%) required a steroid-sparing agent and four (20%) required B-cell depleting therapy (rituximab). The median duration of follow up was 18 months. CONCLUSIONS: This is the first characterised Australian cohort with generalised IgG4RD, a rare, relatively indolent and under-recognised multisystem disorder. Diagnosis is difficult given lack of awareness of this rare condition among physicians, its presentation as a great disease mimic, challenges with histopathological assessment and the absence of a suitable serum biomarker.

Comparison of enzyme-linked immunosorbent assay and rapid chemiluminescent analyser in the detection of myeloperoxidase and proteinase 3 autoantibodies.

Antibodies to myeloperoxidase (MPO) and proteinase 3 (PR3) are vital in the diagnosis and management of ANCA-associated vasculitis. A chemiluminescent immunoassay (CLIA; Quanta Flash) provides MPO and PR3 antibody results in 30 minutes, which is much faster than enzyme-linked immunosorbent assay (ELISA). We compared the performance of ELISA (Orgentec) and CLIA (Quanta Flash) for MPO and PR3 antibody quantitation on 303 samples, comprising 196 consecutive samples received in a single diagnostic laboratory over a 3 month period, and 107 samples collected from 42 known vasculitis patients over a 40 month period. We observed a correlation between both methods using spearman correlation coefficients (MPO, rs = 0.63, p < 0.01; PR3, rs = 0.69, p < 0.01). There was agreement between both methods in determining a positive or negative result. In the vasculitis cohort, CLIA performed well at clinically important stages of disease; diagnosis (eight samples all positive by both assays) and disease relapse (correlation for both MPO and PR3 antibody quantitation rs = 0.84, p = 0.03 and rs = 0.78, p < 0.01, respectively). Three samples were discordant at clinical relapse, testing positive by CLIA, including one high positive associated with relapse requiring a change in treatment. In summary, CLIA appears to be at least as accurate as ELISA for measurement of MPO and PR3 antibodies.