What Are Molecular Diagnostics?

Molecular diagnosis refers to the technology of applying molecular biology methods to detect changes in the structure or expression level of genetic material in patients and make diagnosis. Molecular diagnosis is the main method of predictive diagnosis. It can be used for both individual genetic disease diagnosis and prenatal diagnosis. Molecular diagnosis mainly refers to the detection of genes encoding various structural proteins, enzymes, antigen antibodies, and immune-active molecular genes related to diseases.

Proper specimen collection is essential to ensure specimen integrity and accuracy of qualitative / quantitative detection of nucleic acids. Specimens should be collected in strict accordance with appropriate biosafety guidelines. Improper specimen processing can result in nucleic acid degradation and erroneous patient test results.

Specimen identification

When collecting specimens, the identity of the patients and their specimens should be clarified, and the privacy of patients should be fully respected. At the same time, medical personnel should be provided with reasonable and sufficient information on testing and treatment. Specimens should be affixed securely with at least: identification number, date and time of collection, name of specimen collector, source of specimen, etc.

2. Application Form Information

The application form includes at least the following information: identification number, admission registration number, patient name, date of birth, gender, race, date of collection, specimen type, relevant clinical and laboratory information, doctor's name, department for specimen collection, test application Reasons, etc.

3. Specimen collection

When collecting human tissue or fluid samples, observe relevant safety precautions, wear gloves to prevent the spread of blood-borne pathogens in the samples, and prevent the samples from being contaminated by the shed cells of the processing staff. Certain tests may require additional precautions and collection instructions, such as HPV testing for cervical specimens before the acetic acid test. When adopting different detection methods, laboratories should consider potential sources of interference and pollution, and properly guide and train clinicians to collect samples according to the requirements of specific methods or detection systems. The clinical laboratory should enter the specimen information into the laboratory information system (LIS) as soon as the specimen is received, and it should process the received specimen as soon as possible. Rejection should be considered if the specimen is hemolyzed, frozen, or improperly labeled.

Anticoagulant

Blood and bone marrow aspiration (BMA) specimens should be collected using appropriate anticoagulation tubes or test tubes containing other additives. The choice of test tube additives should be based on the type of analyte, test, and sample size. Studies have shown that heparin and heme may inhibit PCR reactions. Therefore, the use of EDTA and ACD anticoagulants for the detection of plasma or bone marrow aspirate specimens is recommended. If it is measured as intracellular RNA, the device for collecting blood or bone marrow should contain an RNA stabilizer or add an RNA stabilization solution immediately after collection.

5. Organizing specimens

Tissue specimens can be used if blood or oral mucosal cells are not available (such as when the patient dies), or if the tissue specimen is of a different genotype than blood or oral mucosal cells, or if the tissue is the source of some potentially infectious substance nucleic acid. The optimal amount of tissue is usually 1-2 g, but the amount of collected tissue varies depending on the amount of DNA and RNA contained in each tissue. Multicellular tissues such as bone marrow, lymph nodes, and spleen are suitable for genomic DNA testing and require less tissue. Few cell specimens such as muscle, fiber, and adipose tissue are not the best sources of genomic DNA, and the collection volume is preferably greater than 1-2g. Generally, at least 10 g of RNA or DNA is obtained from tissues greater than 10 mg without extensive fatty infiltration. The amount and type of protein varies from tissue to tissue, and nucleic acid isolation methods vary from tissue to tissue. Isolate DNA or RNA according to the tissue of a particular source and according to the manufacturer's recommendations.

Pathologists usually take a representative part of tissue from a large piece of tissue for fixation, staining, microscopic examination and pathological diagnosis, or select a representative tissue to extract DNA or RNA for molecular analysis. Generally, lesion tissue is selected for detection, and non-lesion tissue is used as a control. Control tissue is essential for certain molecular tests, such as loss of heterozygosity analysis or microsatellite instability tests. ^[1]

Molecular diagnostics is one of the important frontiers in the development of contemporary medicine. Its core technology is genetic diagnostics. Conventional technologies include:

(1)

The main technologies of molecular diagnosis include nucleic acid molecular hybridization, polymerase chain reaction and biochip technology.

1. Nucleic acid molecular hybridization technology has a certain complementary sequence and a single strand of nucleotides in the liquid phase or solid phase to associate heteroduplexes according to the principle of base complementary pairing, which is called nucleic acid molecular hybridization. The two sides of the hybridization are the test nucleic acid sequence and the probe sequence. The technology can be used for qualitative or quantitative detection of specific DNA or RNA sequences.

2.

The core technologies of most molecular diagnostic laboratories focus on the detection of specific, relatively short DNA or RNA fragments. The technology can diagnose infectious diseases, identify specific genetic variants that affect drug metabolism, or detect disease-related genes, such as those associated with cancer. At the heart of these tests is real-time quantification

Among them, PCR products occupy the main market for molecular diagnostics, and gene chips are the main trend in the development of molecular diagnostics market. PCR products have high sensitivity, strong specificity, short diagnosis window, and can be used for qualitative and quantitative detection. It can be widely used in hepatitis, sexually transmitted diseases, pulmonary infectious diseases, eugenics, genetic diseases, tumors, etc., filling the early immune detection window The blank test period provides effective help for early diagnosis, early treatment, and safe blood use. Gene chips are molecular biology,

Countries around the world attach great importance to the development of molecular diagnostic technology, and gene chips will become the mainstream of the development of new-generation molecular diagnostic reagents. The gene chip is the crystallization of a combination of molecular biology, microelectronics, computer and other disciplines. It integrates a variety of modern and sophisticated technologies, and is praised by experts as "the ultimate product in the diagnostic industry". The gene chip has the function of being able to detect multiple targets at the same time, and it is fast and effective. Therefore, the gene chip has become the main development direction of the new generation of molecular diagnostic reagents, but its cost is high, the development is difficult, the product variety is very small, and it is only used for scientific research and drug screening. The large-scale clinical application of gene chips still has unsolved technical defects, which are mainly due to the low specificity and sensitivity of chip diagnostics, the high cost of chip diagnostics, and the high cost of chip diagnostic equipment. Globally, although only a few chips can be used for clinical diagnosis, domestic gene chip technology has already taken the lead in the world. Gene chip technology will be the most challenging potential opponent of real-time PCR detection technology, mainly: real-time PCR technology can only detect one or a few target genes at a time, while gene chip technology can achieve the simultaneous detection of a large number of target genes. With the progress of the Human Genome Project, gene chips have become a hot spot in research at home and abroad. If the gene chip technology matures rapidly and is industrialized on a large scale, it will have a greater impact on the real-time PCR detection. However, the large-scale clinical application of gene chips still has unsolved technical defects, mainly due to the low specificity and sensitivity of chip diagnostics, the high cost of chip diagnostics, and the high cost of chip diagnostic equipment. Stay ahead for 5 to 10 years. ^[3]