In vitro diagnostics (IVD) obtains clinical diagnostic information by detecting human samples (blood, body fluids, tissues, etc.) to determine disease or body function. In vitro diagnosis consists primarily of diagnostic equipment and diagnostic reagents.IVD reagents are reagents，kits，calibrators and quality control products, etc., which are used for in vitro detection of human samples (body fluids, cells, tissue samples, etc.) in disease prevention, diagnosis, treatment monitoring, prognosis observation, health status evaluation, and genetic disease prediction. IVD reagents mainly include biochemical diagnostic reagents, immunodiagnostic reagents, molecular diagnostic reagents, microbial diagnostic reagents, urine diagnostic reagents, blood coagulation diagnostic reagents, hematology and flow cytological diagnostic reagents. Biochemical, molecular diagnostic and immunological reagents are the three major categories of diagnostic reagents.

Biochemical diagnostic reagents are reagents for measuring biochemical indicators in vivo through various biochemical reactions or immune reactions. They are mainly used for testing with manual, semi-automatic, and fully automatic biochemical analyzers to measure enzymes, sugars, lipids, proteins and non-protein nitrogen, inorganic elements, liver function and other indicators.

Molecular diagnostic reagents are mainly reagents for measuring disease-related proteins and various immunologically active molecules and genes encoding these molecules, and are mainly used for detection of hepatitis, sexually transmitted diseases, pulmonary infectious diseases, prenatal and postnatal diseases, genetic diseases, tumors, and more. Molecular diagnostic reagents mainly include nucleic acid amplification technology (PCR) products, gene chips, and protein chip products.

The immunodiagnostic reagents are reagents determined by a specific reaction combining antigen and antibody, and can be classified into radioimmunoassay, colloidal gold, enzyme-linked immunosorbent assay, time-resolved fluorescence, immunohistochemistry and chemi-luminescence. Immunodiagnostic reagents are mainly used for the treatment of infectious diseases, endocrine, tumor, drug testing, blood type identification, etc.

Biomarkers have been used for in vitro diagnostics for a long time. Biomarkers are a class of indicators that objectively evaluate normal physiological status, pathological processes, or body reactions after drug intervention. It can reflect the characteristic changes that occur when a living organism interacts with the environment. As an auxiliary means, biomarkers help to judge the occurrence, development and prognosis of diseases early, quickly, accurately and sensitively. Biomarkers are used for the diagnosis and classification of diseases to monitor the development and severity of the disease, to test the clinical treatment effect and to predict the risk of individual morbidity. Also, biomarkers can be used for high-risk population screening. In brief, biomarkers are divided into small molecule biomarkers, macromolecular biomarkers (including nucleic acids, proteins, carbohydrates, and lipids), complex biomarkers, and bio-population biomarkers.

1. Small molecule biomarkers

There are many kinds of small molecule compounds, which are the material basis for maintaining the life activities and biochemical metabolism of the body. At the same time, some small molecular substances will also cause damage to the body. Therefore, characteristic changes that occur in the body, such as changes in concentration, abnormal appearance or disappearance, can be used as indicators for detecting diseases. Blood glucose concentration or urine glucose concentration can be used as the basis for clinical judgment of diabetes; the creatinine concentration reflects renal function; the total cholesterol level is closely related to the incidence of atherosclerosis and coronary heart disease.In addition, acute or chronic poisoning caused by some toxic small molecule compounds, such as aflatoxin, cyclosporin A and nitrosourea dichloride, can be screened by mass spectrometry to provide a basis for timely diagnosis and treatment.

2. Macromolecular biomarkers

2.1 Nucleic acids biomarkers

Changes in RNA levels in the body can reflect changes in the physiological and pathological state of the body. It has been reported in the literature that the use of chip technology to compare the changes in RNA levels of gene transcription under physiological and pathological conditions, to find the correlation between disease and specific RNA abnormalities, can be used for disease judgment. In recent years, research on RNA biomarkers has received much attention. In addition to proteins, circulating microRNAs (miRNAs) in serum are another non-invasive biomarker with good stability and reproducibility, which can be used to diagnose neurodegenerative diseases. For example, the level of miRNA in the cerebrospinal fluid of patients with primary central nervous system lymphoma is significantly negatively correlated with the therapeutic effect, so it can be used as a biomarker for monitoring the therapeutic effect. In addition, long-chain non-coding RNA can affect the occurrence and development of tumors, and is considered to be a promising tumor biomarker. DNA is the direct carrier of the genetic material of the body. Mutation or modification of some important genes causes the signal pathway to be continuously activated or inactivated by causing the function of the corresponding gene to be deleted or obtained, resulting in dysfunction of the body and even serious diseases. Numerous studies have confirmed that inactivating mutations of important tumor suppressor genes such as p53, Rb and PTEN, or activating mutations of important protooncogenes such as ras and myc are the important reasons for tumorigenesis. It is currently clinically possible to predict the likelihood of breast and ovarian cancer by detecting whether breast cancer susceptibility gene 1 (BRCAl) and BRCA2 have genetic mutations. In addition, some potential DNA biomarkers, such as basic nuclear protein 1 (basonucin 1) and metal peptidase containing thrombospondin 1 genes, have significantly increased methylation levels in pancreatic cancer, so their degree of DNA methylation can be as a biomarker for early detection of pancreatic cancer.

2.2 Carbohydrates and lipids biomarker

Substances such as sugars and lipids play an important role in life activities, including material metabolism, cell recognition, and immunity. Therefore, they can also be used as biomarkers for disease diagnosis. Sphingolipidosis is caused by the genetic deficiency of the related sphingolipid metabolism enzyme in the lysosome, which causes the sphingolipid to destabilize and accumulate, resulting in organ damage. Therefore, according to the types of their storage products such as glucosyl sphingolipid, trihexosyl sphingosine and galactosyl sphingosine, the disease classification can be classified for sphingolipidosis.

2.3 Proteins biomarker

As a direct performer of life activities, proteins participate in almost all processes of life, including gene expression regulation, cytoskeleton formation, substance transport, metabolism, and immune response. Therefore, the protein can be used as an indicator for objective evaluation of normal physiological functions or pathological conditions.The most typical example is alpha-fetoprotein as a diagnostic biomarker for liver cancer.AFP is a biologically active protein with a structure similar to human serum albumin and a molecular weight of approximately 70 kDa. AFP above a certain value (generally greater than 400μg / L for more than 1 month, except pregnancy, reproductive-derived tumors, active liver disease, etc.) can be used for the definitive diagnosis of primary liver cancer.In addition, biomarkers for diagnostic antibodies are used for in vitro diagnosis of tumors, acute kidney injury, and autoimmune diseases.

Bladder cancer is a common urinary system tumor. About 70% of bladder cancers are superficial, and endoscopic transurethral resection can have a good effect. However, 50% to 70% of patients have recurrence after surgery, and 10% to 15% of them will develop into the invading muscle layer. Due to this recurrence of bladder cancer, patients require long-term follow-up. Urine cytology has long been used to diagnose and follow up superficial bladder cancer. Its specificity is high, especially for highly differentiated tumors, but its sensitivity is poor. Currently, some tumor markers in urine have been studied to diagnose bladder cancer.Kinase-type plasminogen activator (uPA) is involved in tumor invasion and metastasis by regulating the proteolysis, adhesion, and movement of tumor cells. uPA is a serine protease that catalyzes the conversion of plasminogen to plasmin. Fibrinolytic enzymes destroy the basement membrane and extracellular matrix, thereby facilitating the invasion of tumor cells into lymphatic vessels and blood vessels. The precursor of uPA is inactive and catalyzes the conversion of plasminogen to plasmin when it binds to a specific cell surface receptor (uPAR). Elevated levels of uPA and/or uPAR may be associated with progression and prognosis of the lesion.NMP22 is a member of the nuclear matrix protein family and is a subunit of the nuclear mitotic machinery. Tumor cells are mitotic, and the content of NMP22 is more than 100 times higher than that of normal tissues. NMP22 enters the urine and can be used as a tumor marker. NMP22 in urine can be detected by polyclonal anti-NMP22 test or NMP22 bladder check.The expression level of prostate specific antigen (PSA) in serum is very low in normal males. PSA levels were significantly elevated in the serum of patients with prostate cancer. Therefore, clinically, the risk of prostate cancer can be indicated by detecting PSA levels in serum. The level of human epididymis protein (HE4) is closely related to the disease of ovarian cancer, and the level of HE4 in 88.0% of patients with ovarian cancer is significantly increased. Especially in the early stage of ovarian cancer, the sensitivity and specificity of HE4 diagnosis were 82.7% and 99.0%, respectively, while the biomarker CAl25 was only 45.9% and 20.0%. Serum thyroglobulin levels are positively correlated with tumor size and tumor metastasis, and can be used clinically for prognosis of thyroid cancer. Carcinoembryonic antigen is a broad-spectrum tumor marker, and its level is elevated in the serum of tumor patients such as colorectal cancer and lung cancer. It is clinically used for monitoring and prognosis of such tumors. In addition, many protein biomarkers have been discovered and validated. The level of RAB27A protein in glioma tissues is closely related to the type and malignancy of glioma, and can be used as a biomarker for disease classification and prognosis. Increased levels of heat shock protein (HSP) 72 in urine can predict acute kidney injury with sensitivity, specificity, and accuracy of 100%, 83.3%, and 90.9%, respectively.The severity of tuberculosis, pneumonia and chronic obstructive pulmonary disease can be judged by detecting whether pulmonary surfactant protein D is elevated in serum.