Erratum in Dig Dis Sci. 2015 Dec;60(12):3827. BACKGROUND: In assessing Crohn's disease (CD) activity, C-reactive protein (CRP) is an important indicator of inflammation; however, it is not necessarily associated with the Crohn's Disease Activity Index (CDAI), particularly in patients with low CRP. Recently, platelet activation factors have been recognized due to their importance in the inflammatory response. In this study, we examined associations between the CDAI and platelet factor 4 (PF-4), β-thromboglobulin (β-TG), and other coagulation and fibrinolysis factors. AIMS: We aimed to find a new marker for evaluating disease activity in patients with CD and low CRP. METHODS: Nine markers, including CRP, platelet count, white blood cell count, fibrin and fibrinogen degradation product, fibrinogen, thrombin-antithrombin complex, prothrombin fragments 1 + 2, PF-4, and β-TG were evaluated in 47 patients with CD and low CRP (<1.0 mg/dl). Patients were assigned to high or low disease activity groups, CDAI-H (CDAI ≥ 150) and CDAI-L (CDAI < 150), respectively. RESULTS: CDAI-H exhibited significantly higher PF-4 and β-TG levels than CDAI-L (P < 0.01). Other markers were not significantly different between groups. CDAI was positively correlated with the levels of PF-4 and β-TG (P = 0.0033 and 0.0024; r = 0.4202 and 0.4321, respectively). Receiver operating characteristic curve analyses of PF-4 and β-TG showed high sensitivity (61.9 and 81%, respectively) and specificity (84.7 and 69.2%, respectively) for diagnosing active CD. CONCLUSION: Among eight potential markers, PF-4 and β-TG were the most highly correlated with CDAI in patients with CD and low CRP. PF-4 and β-TG levels showed promise as new markers for assessing CD in patients with low CRP.