Pancreatitis-associated protein (PAP) is a pancreatic stress protein also expressed in the ileum but not in the colon. Its serum concentration is increased in patients with small bowel inflammation due to untreated celiac disease. We searched to determine whether PAP could be a serum marker for ileal location of active Crohn's disease (CD).

A multicenter prospective study was conducted, including 54 healthy controls and 124 patients with CD of whom 38 had quiescent ileal or ileocolonic disease (group A), 45 had active ileal or ileocolonic disease (group B), 18 had quiescent colon-only CD (group C), and 28 had active colonic disease (group D). Active disease was defined by a Crohn's disease activity index > 150 and serum C-reactive protein (CRP) > 10 mg/mL. Location of lesions was assessed by endoscopy. PAP was assayed in serum, the upper threshold for normal values being 50 ng/mL.

In group B, 27 patients (60%) had elevated serum PAP, compared to one in group A (2.5%), one in group C (5.3%), three in group D (10.7%) and none in the control group (P < 0.01). By contrast, serum levels of C-reactive protein did not differ between patients with active CD and either ileal location (group B) or pure colonic location (group D) (38 ±10.5 vs 41.6 ± 6.4 mg/mL, NS). Within group B, serum PAP concentration was correlated with none of the epidemiological, clinical or biological data available. Increased serum level of PAP diagnosed ileal location in active CD with a sensitivity of 60 %, a specificity of 94%, a positive predictive value of 84% and a negative predictive value of 81%.

Elevated serum PAP (> 50 ng/mL ) is significantly associated with disease activity and ileal location