Primary sclerosing cholangitis (PSC) predisposes to the development of cholangiocarcinoma, a usually fatal complication that is difficult to diagnose. Serum concentrations of CA 19‐9, a tumor‐associated antigen, are frequently increased in patients with only cholangiocarcinoma. The aim of this study was to assess the value of an increased serum CA 19‐9 level for the diagnosis of cholangiocarcinoma in patients with preexisting PSC. We analyzed serum samples from 9 patients with PSC and superimposed cholangiocarcinoma and from 28 patients with only PSC. Serum concentrations of CA 19‐9 were measured in a blinded manner with use of an immunoradiometric assay. The serum CA 19‐9 concentrations were increased in 8 of 9 patients (89) with PSC and cholangiocarcinoma (mean±SE, 391 ± 86 U/ml; range, 4 to 677), whereas they were increased in only 4 of 28 patients (14) with only PSC (mean ± SE, 61 ± 16 U/ml; range, 2 to 370). The sensitivity of a CA 19‐9 value greater than 100 U/ml for cholangiocarcinoma in PSC was 89, and the specificity was 86. The measurement of serum concentrations of CA 19‐9 is a promising test for detecting cholangiocarcinoma in patients with PSC.
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