There is an increase in serum IgG levels especially. It was initially reported that elevation of IgG4 (> 135 mg/dl) had a 95% sensitivity and 97% specificity; however, subsequent studies have reported the sensitivity and specificity IgG4 (> 140 mg/dl) at 76 and 93% respectively. The greatest value of serum IgG4 is when it is twice the upper limit of normal (> 280 mg/dl) as it is 99% specific for AIP at this level. This is crucial because AIP is a rare disease and any loss in specificity drastically reduces the positive predictive value and increases the false-positive rate. A total of 10% of pancreatic cancers have abnormal IgG4 levels. Conversely, even in the presence of classic histological features and tissue IgG4 staining, serum IgG4 can be normal. As discussed before, a host of autoantibodies have been described in the literature but do not seem to add significantly to the sensitively and specificity of serum IgG4.[4,5,35,36,37] In addition to the aforementioned features the presence of high levels of Ca 19-9 (> 150 mg/dl) in the absence of biliary obstruction or after decompression of the obstruction is highly suggestive of pancreatic cancer.
Expert Rev Gastroenterol Hepatol. 2009;3(2):197-204. © 2009 Expert Reviews, Ltd.
Cite this: Autoimmune Pancreatitis: An Update - Medscape - Apr 01, 2009.