目的·研究肺癌和肺炎患者血清小分子代谢物的变化，评估相关代谢产物在肺癌和肺炎鉴别诊断中的效能，并建立诊断模型。方法·运用液相色谱-串联质谱法分别对95例肺癌患者（肺癌组）、69肺炎患者（肺炎组）和90例健康体检人群（对照组）血清中的小分子代谢物进行检测，包括13种氨基酸和15种胆汁酸。采用t检验和Mann-Whitney U 检验分析组间差异；采用二元Logistic回归筛选优化诊断指标并建立诊断模型；采用受试者工作特征曲线（receiver operating characteristic curve，ROC）分析单项指标和联合诊断模型对肺炎和肺癌的鉴别诊断价值。结果·与对照组相比，肺炎患者血清中3种氨基酸、7种胆汁酸显著降低，1种氨基酸、2种胆汁酸显著增高；肺癌患者血清中6种氨基酸、2种胆汁酸显著降低，2种氨基酸、4种胆汁酸显著增高；脱氧胆酸是鉴别诊断能力最强的单个代谢产物；筛选出瓜氨酸、苯丙氨酸、脱氧胆酸建立肺癌和肺炎的鉴别诊断模型，模型的ROC曲线面积为0.829，最佳临界值为0.55，此处诊断灵敏度为76.8%，特异度为79.7%，符合率为78.3%。结论·肺炎患者和肺癌患者的一些血清小分子代谢产物发生了显著变化，相关代谢产物组成的联合诊断模型具有对肺癌和肺炎进行鉴别诊断的潜在价值。

Objective · To study on the changes of serum small metabolites in patients with lung cancer and pneumonia, assess the performance of these metabolites on differential diagnosis between lung cancer and pneumonia, and establish diagnostic model. Methods · Liquid chromatography tandem mass spectrometry(LC-MS/MS) was applied to test the serum metabolites, including 13 amino acids and 15 bile acids, of 95 patients with lung cancer, 69 patients with pneumonia and 90 healthy people. T test and Mann-Whitney U test were used to analyze the differences among the three groups. Binary logistic regression was applied to screen valuable indexes and establish diagnostic model. The receiver operating characteristic curve (ROC) was used to compare the differential diagnostic value of single index and diagnostic model. Results · Compared with the control group, 3 kinds of amino acids and 7 kinds of bile acids were decreased significantly, while 1 kind of amino acid and 2 kinds of bile acids were increased significantly in pneumonia patients. 6 kinds of amino acids and 2 kinds of bile acids were decreased significantly, while 2 kinds of amino acids and 4 kinds of bile acids were increased significantly in lung cancer patients. Deoxycholic acid was the most valuable metabolite in differential diagnosis. Citrulline, phenylalanine and deoxycholic acid were screened to establish differential diagnostic model of lung cancer and pneumonia. The area under curve (AUC) of the model was 0.829, and the Cut-Off value was 0.55，while the sensitivity was 76.8%, the specificity was 79.7%, and the coincidence rate was 78.3%. Conclusion · This study revealed that some small metabolites in serum of the patients with pneumonia and lung cancer have changed significantly. The diagnostic model composed of some metabolites has the potential value to assist differential diagnosis of lung cancer and pneumonia.