BackgroundReactive thrombocytosis occurs secondary to systemic infections, inflammatory, and other conditions. The relationship between thrombocytosis and acute pancreatitis (AP) in inflammatory diseases is uncertain. This study aimed to evaluate the clinical significance of thrombocytosis in AP patients during hospitalization.MethodsSubjects within 48 h of AP onset were consecutively enrolled over 6 years. Platelet counts of ≥ 450,000/µL were defined as thrombocytosis, < 100,000/µL as thrombocytopenia, and other counts as normal. We compared clinical characteristics, including the rate of severe AP (SAP) assessed by the Japanese Severity Score; blood markers, including hematologic and inflammatory factors and pancreatic enzymes during hospitalization; and pancreatic complications and outcomes in the three groups.ResultsA total of 108 patients were enrolled. Although, SAP was more common in patients with thrombocytosis and thrombocytopenia (87.9% and 100%, respectively), the differences in lymphocytes and C-reactive protein, lactase dehydrogenase, and antithrombin levels, which are factors of the systemic inflammatory response, and the mean platelet volume, an indicator of platelet activation, were observed among patients with thrombocytosis and thrombocytopenia during hospitalization. Regarding pancreatic complications and outcomes, patients with thrombocytosis and thrombocytopenia had higher acute necrotic collection (ANC), pancreatic necrosis, intestinal paralysis, respiratory dysfunction, and pancreatic-related infection levels than patients with normal platelet levels. The relationship between pancreatic complications and thrombocytosis was assessed by multivariate logistic regression; the odds ratios for development of ANC, pancreatic necrosis and pancreatic-related infections were 7.360, 3.735 and 9.815, respectively.ConclusionsThrombocytosis during hospitalization for AP suggests development of local pancreatic complications and pancreatic-related infections.