Value of serum IgG4 in diagnosis of IgG4-related disease and in differentiation from rheumatic diseases

Abstract

Objective To investigate the value of serum IgG4 in diagnosis of IgG4-RD and in differentiation from rheumatic diseases. Methods Total of 23 patients with IgG4-RD and 502 patients with rheumatic diseases were enrolled, who presented at Changhai Hospital in 2010 to 2011.In the study, rheumatic diseases were categorized into groups of Sjgren syndrome (n=26), ankylosing spondylitis (n=50), systemic sclerosis (n=3), rheumatoid arthritis (RA，n=125), mixed connective tissue disease (n=15), systemic lupus erythematosus (SLE，n=212), adult onset still disease (n=20), Behcet syndrome (n=17), polymyositis (n=12), dermatomyositis (n=12), polymyalgiarheumatica (n=10).Serum IgG and IgG4 levels were measured by a rate nephelometer assay.The ROC curves were constructed to identify the optimal serum IgG4 cutoff value for diagnosing IgG4-RD and evaluate its sensitivity and specificity. Results The mean levels of serum IgG4 in the group with IgG4-RD were 11.4（5.0-14.8） g/L.In about 95.6% IgG4-RD patients, the serum IgG4 level was higher than>1.4 g/L and other rheumatic diseases (U values were 6.0，21.0，0，58.5，0，9.0，3.0，4.0，0，3.0，3.5，P 1.4 g/L, which was about 10% in the patients whith RA, ankylosing spondylitis, adult onset still disease and polymyalgiarheumatica.According to the ROC constructed the cut off value in present study was 2.2 g/L, and sensitivity and specificity were 95.7% and 97.4%, respectively.Area under the curve (AUC) was 0.995. There were no significant differences between the sensitivity and specificity values obtained with a cutoff value of 2.2 g/L.In patients with other rheumatic diseases, the ratio of high serum IgG4 level (>2.2 g/L) were declined obviously, except polymyalgiarheumatica, it was less than 10%.For differentiation from rheumatic diseases specificity values were higher. Conclusions The cut off value of 2.2 g/L is useful for diagnosing IgG4-RD, and in differentiation from rheumatic diseases.The high serum IgG4 concentrations are not specific to IgG4-RD.The cut off value of 2.2 g/L is better to diagnose IgG4-RD, and contributes to the differential diagnosis of IgG4-RD and other rheumatic diseases, but it needs to be further confirmed in clinical practice.(Chin J Lab Med, 2012,35:1029-1033) Key words: Immunoglobulin G; Autoimmune diseases; Pancreatitis; Rheumatic diseases; Diagnosis; differential