This study investigates the changes in diamine oxidase (DAO) and D-lactate levels in cancer patients undergoing chemotherapy and their clinical significance in evaluating intestinal barrier function. Breast and gynecologic cancer patients who received chemotherapy between January 2020 and December 2023 were enrolled from our hospital. Blood samples were taken before chemotherapy, within 3 days after chemotherapy, and before the next course of chemotherapy. The level of plasma DAO and D-lactate were measured by enzyme-linked immunosorbent assay (ELISA). After chemotherapy, nutritional markers such as albumin (ALB) and prealbumin (PAB) were evaluated. Anorexia, vomiting, nausea and diarrhea were evaluated during the chemotherapy cycle. There were no notable differences in serum DAO and D-lactate levels before chemotherapy among different tumor types, tumor stage and chemotherapy type. Serum DAO and D-lactate levels after chemotherapy were significantly elevated compared to their levels before chemotherapy (P <
.05). The plasma DAO and D-lactate levels in cancer patients before the next course of chemotherapy were higher than those observed before the initial treatment, but the difference failed to achieve statistical significance (P >
.05). The levels of DAO before chemotherapy were higher in patients with diarrhea and anorexia after chemotherapy than those without diarrhea and anorexia (P <
.05). The levels of D-lactate before chemotherapy were notably elevated in patients with vomiting, diarrhea and nausea after chemotherapy than those without vomiting, diarrhea and nausea (P <
.05). Monitoring serum levels of DAO and D-lactate in cancer patients undergoing chemotherapy can serve as indicators for evaluating gastrointestinal dysfunction and nutritional status.