Utility of slot-blot-ELISA as a new, fast, and sensitive immunoassay for detection of carcinoembryonic antigen in the urine samples of patients with various gastrointestinal malignancies.

Carcinoembryonic antigen (CEA) is the most widely used clinical tumor marker. CEA immunoassay has found acceptance as a diagnostic adjunct in clinical diagnosis of gastrointestinal tumors (GIT). Several immunoassays have been established for detection of CEA in plasma, serum, tissue, feces, and urine of cancer patients using polyclonal or monoclonal antibodies raised against CEA. Some of these assays display both high sensitivity and specificity for the detection of CEA. However, these assays require special and highly expensive equipment and the procedures require long periods for their completion. In the present study, we established a Slot-Blot Enzyme Linked Immunosorbent Assay (SB-ELISA), based on anti-CEA monoclonal antibody (CEA-mAb), as a new, simple, fast, cheap, and non-invasive immunodiagnostic technique for detection of CEA in the urine of GIT patients. Urine and serum samples were collected from 248 GIT patients (58 with pancreatic cancer, 20 with hepatoma, 23 with ampullary carcinoma, 15 with hilar cholangiocarcinoma, 28 with gastric cancer, 14 with esophageal cancer, and 90 with colorectal cancer). Moreover, urine and serum samples were collected from 50 healthy individuals to serve as negative controls. The traditional ELISA technique was used for determination of CEA in the sera of GIT patients using anti-CEA monoclonal antibody. A comparison between the results of both techniques (ELISA and SB-ELISA) was carried out. The traditional ELISA detected CEA in the sera of 154 out of 248 GIT patients with a sensitivity of 59.8%, 51.7% positive predictive value (PPV) and 75.37% negative predictive value (NPV). In addition, it identified 15 false positive cases out of 50 healthy individuals with a specificity of 70%. The urinary CEA was identified by a Western blotting technique and CEA-mAb at a molecular mass of 180 Kda. The developed SB-ELISA showed higher sensitivity, specificity, PPV, and NPV (70.1%, 78%, 62.4%, and 82.13%, respectively) for detection of CEA in the urine of GIT patients. The semi-quantitative SB-ELISA showed a higher overall efficiency of 72.8% versus 63.4% in the case of the quantitative ELISA, for detection of CEA. In conclusion, SB-ELISA is more efficient for detection of CEA in gastrointestinal tumors. It is a simple, rapid, non-invasive, and sensitive assay. Moreover, all steps of the SB-ELISA are performed at room temperature, without the use of expensive equipment; this may enhance the application of this assay in field studies and mass screening programs.