Tumor markers are a type of substance synthesized and released by tumor cells themselves, or produced by the body in response to tumor cells. These substances can reflect the phenotype and genetic characteristics of various stages of cellular malignancy, mainly including proteins, carbohydrates, and enzymes. There are many methods for detecting tumor markers, including radioimmunoassay, enzyme-linked immunosorbent assay, chemiluminescence immunoassay, electrochemiluminescence immunoassay, protein chip assay, etc. Different methods, instruments, and reagents will yield different results. So, how do we usually collect specimens when detecting tumor markers? What are the testing principles of its laboratory?
1、 Sample for detecting tumor markers
1. Serum sample. The detection of tumor markers is often carried out through blood collection. Blood can be collected from patients on an empty stomach in the morning and sent to the laboratory to check the content of tumor markers in the blood.
2. Chest and ascites specimens. Sometimes, pleural effusion or ascites can also be drained and sent for tumor marker examination. The changes in tumor marker content indicators in pleural effusion and ascites can be compared with the changes in tumor marker indicators in the patient's blood, thereby strengthening disease monitoring and diagnosis.
2、 The laboratory detection principle of tumor markers
There are many detection principles for tumor markers. This article mainly introduces the most commonly used experimental principles in laboratories, namely enzyme-linked immunosorbent assay and chemiluminescence assay. The specific principles are as follows:
1. Enzyme linked immunosorbent assay
Enzyme linked immunosorbent assay is to first bind a known antibody or antigen to a solid carrier and maintain its immune activity. During the measurement, the sample to be tested and the enzyme-linked antigen or antibody are reacted with the antibody or antigen adsorbed on the surface of the solid-phase carrier in different steps. Wash away excess antigen antibody complexes and free components. Then add the enzyme to catalyze the color development of the substrate for qualitative or quantitative determination.
2. Chemiluminescence method
Chemiluminescence labeled immunoassay, also known as chemiluminescence immunoassay, is an immunoassay instrument that directly labels antigens or antibodies with chemiluminescence agents. The chemiluminescence immunoassay analyzer consists of two parts, namely the immune response system and the chemiluminescence analysis system. The immune response system directly labels luminescent substances on antigens (chemiluminescence immunoassay) or antibodies (immunohistochemistry immunoassay) or enzymes act on luminescent substrates, and the antigen antibody reaction involves unknown and known relationships. If the analyte is the test antigen, then the antibody is already known. If the analyte is the test antibody, then the antigen is known. Because the intensity of the light signal is directly proportional to the concentration of the analyte, it can be converted through relevant equations. The chemiluminescence analysis system utilizes chemiluminescent substances catalyzed by catalysts and oxidized by oxidants to form an excited intermediate state. When this excited intermediate state returns to a stable ground state, it simultaneously emits photons. When the photons are emitted, the core detection device in the chemiluminescence immunoassay instrument, namely the photomultiplier tube, is detected by a single photon and transmitted to the amplifier. The amplifier amplifies the analog current into a digital current, and the digital current transmits the luminescence signal to the computer through the R232 data line for calculation, obtaining clinical results.
Regarding the reference range of tumor markers, there will definitely be some differences in different regions, populations, methods, reagents, and equipment, but only in the magnitude of the differences. So, when you see inconsistent results of tumor markers on the test report, don't panic, first understand the detection principle and then analyze the results.