What is Clinical Biochemistry?

Clinical biochemistry is based on the normal biochemical metabolism of the human body, and studies the basic theory of pathological changes in biochemistry and the changes in the quality and quantity of relevant metabolites under the state of the disease, in order to diagnose clinical experiments of diseases, monitor treatment, and drugs. A subject that provides information and decision-making basis in the aspects of efficacy and prognosis judgment and disease prevention. It is a rapidly developing independent discipline. Its main task is to use the theories and technologies of physics, chemistry, biology, genetics, pathology, immunology, biochemistry and molecular biology to explore the pathogenesis of diseases and study specific chemical markers in the pathological process. Or changes to specific components in the body.

Clinical biochemistry

Clinical biochemistry is based on the normal biochemical metabolism of the human body, and studies the basic theory of pathological changes in biochemistry and the changes in the quality and quantity of relevant metabolites under the state of the disease, in order to diagnose clinical experiments of diseases, monitor treatment, and drugs. A subject that provides information and decision-making basis in the aspects of efficacy and prognosis judgment and disease prevention. It is a rapidly developing independent discipline. Its main task is to use the theories and technologies of physics, chemistry, biology, genetics, pathology, immunology, biochemistry and molecular biology to explore the pathogenesis of diseases and study specific chemical markers in the pathological process. Or changes to specific components in the body.

Chinese name

Clinical biochemistry

main mission

Using physics to explore the pathogenesis of diseases

Subject type

A theoretical and practical applied discipline

Main foundation

Chemical and medical knowledge

main effect

Explain about biochemical changes of diseases, etc.

Broadly speaking

Provide information and theoretical basis in all aspects

Clinical biochemistry is a combination of chemistry, biochemistry and clinical medicine, and has developed into a mature independent

1. Explain the biochemical basis of the disease and the biochemical changes in the occurrence and development of the disease. These biochemical changes can be primary, or they can be a series of secondary changes in the biochemical composition of the body fluid caused by organ damage or complications for some reason. This part is also called chemical pathology.

2. Develop and apply clinical biochemical testing methods and technologies, and evaluate the data of the test results and their clinical significance to help clinical diagnosis and take appropriate treatment. This part of the content has two aspects of emphasis: in terms of clarifying the principles of biochemical diagnosis of diseases, focusing on discussing the biochemical mechanism of diseases, which is closer to that of chemical pathology.

Clinical biochemistry traces its development process. It is interconnected and interrelated with many related disciplines (including chemistry, physiology, pharmacology, pathology, clinical medicine, etc.)

The term "clinical chemistry" was used more widely after the Second World War and in the 1950s. Before the 19th century, there were only some chemists, physiologists and clinicians studying changes in the chemical composition of the human body during health and disease, including substances such as proteins, sugars and inorganic substances in the blood and urine. In 1918, Lichtwitz first adopted "Clinical Chemistry" as the textbook title.

After the principles of method establishment in clinical biochemistry are determined, appropriate conditions need to be selected according to the principles to ensure the reliability of the established method. The following uses photometric method as an example to introduce the main steps of condition selection. The color reaction is the basis of photometric analysis. Therefore, the color reaction used for photometry must have at least the following: the reaction has a high specificity, so the interference is small; the colored substance produced by the reaction has a large absorption coefficient, and the greater the sensitivity ; The dissociation degree of the colored product should be small and stable when it is small; in addition, the colored product is required to have a constant composition to make the produced color stable. There are many factors that affect the color reaction, such as temperature, pH, reagent concentration, reaction time and so on. These factors must be tested individually when establishing a new method to determine the best experimental conditions.

Choose the right absorption spectrum

It is actually measuring the light absorption curve produced by the color reaction. The method is to space the entire visible light region (400-700nm) by 10nm (it should be further subdivided near the maximum absorption wavelength range). Divided into dozens of points to measure its absorbance at different wavelengths, and then draw the light absorption curve with the absorbance as the ordinate and the wavelength as the abscissa. Where conditions permit, a dual-beam spectrophotometer should be used for wavelength scanning in the visible light region, and the results are more reliable. At the same time, the absorption curve of the color product of the blank solution and the standard should be measured separately by the same method. The purpose of measuring the light absorption curve is to find the maximum absorption wavelength as the basis for the photometric wavelength selection. Because measured at the maximum absorption wavelength, the maximum sensitivity can be obtained, and it can be more in line with Beer's law. However, in actual use, we cannot simply consider the high sensitivity, but also whether we can meet the Beer's law in the concentration range, and can read the reading in the accurate area of the photometer (absorbance between 0.2-0.85). Sometimes because the measured maximum absorption wavelength is not the characteristic absorption wavelength of the substance to be measured, that is, there are interfering substances with similar maximum absorption at the same time, in order to ensure the specificity of the experiment, it is often changed to a unique rather than the maximum absorption wavelength for measurement. For example, the blood glucose is measured with phosphomolybdic acid, and the wavelength is 420nm. The absorption of the solution at this wavelength is lower than that of other wavelengths of light. The purpose is to make the reference value have a lower absorption, which can allow higher values in the same situation. Reference blood glucose can also be accurately read. Because in this measurement, hyperglycemia is a common direction of change.

Concentration range applicable to the measurement method

According to the law of light absorption, the absorbance of a solution should be proportional to the concentration of the solution. However, due to the ionization, hydrolysis, and association of colored substances, when the solution is diluted or concentrated, the color depth of the colored substances does not decrease or increase in proportion, so it does not conform to the law of light absorption. The applicable concentration range of the measurement method means that the concentration range to be analyzed is in a linear linear section, and the ratio of concentration to absorbance is a constant. At this time, the slope tan at any point on the line is equal, that is:

tan = A1 / C1 = A2 / C2 = A3 / C3 = = An / Cn = K

Here K is the correction constant and can be used for result calculation.

Usually dilute solutions conform to Beer's law, but they are not always straight when the concentration is too high or too low, indicating that the low concentration part also has the limitation of the sensitivity of the instrument and the detection ability of the method. It is performed within the linear range of concentration. This can also be used to determine the amount of specimens, so that the results of clinically significant specimens fall within a linear range.

Observe factors affecting color response

The main factors affecting the color reaction are: the influence of solution pH, the influence of impurities, the temperature and time of the reaction, and the stability of the color. These are the main sources of photometric errors. All need to be observed and controlled within a suitable range through experiments. So as to ensure the accuracy and precision of the method.

Effect of solution pH The color of some solutions is very sensitive to changes in pH. For example, albumin can be changed from yellow to green after combining with bromocresol green at about pH 4. The shade of green is proportional to the albumin concentration, but bromocresol green itself is a pH indicator. Yellow changed to green and changed from green to yellow at pH 3.8. In the color reaction of albumin and bromocresol green, if the pH is not well controlled, errors are easy to occur. For example, each enzyme has its own optimal pH. In the enzymatic reaction, only the optimal pH can be used. Full catalytic activity. Therefore, when establishing the method, it can be made to react under different pH conditions (other conditions are unchanged) to observe the change in absorbance of the color reaction, so as to select a suitable pH range to ensure the color reaction in order to obtain higher sensitivity and Better linearity. Sometimes it is necessary to use the corresponding pH buffer solution to maintain the pH of the reaction in order to facilitate the normal progress of the color reaction.

The effect of impurities is because clinical biochemical specimens contain many non-measurement substances in addition to the test substance. The composition is very complex. Some of them can interact with colored products to gradually fade the produced color, and some are similar to the test substance. It can also slowly form colored compounds or precipitates with color-developing reagents, and some of them are colored, etc., which will affect the color of the test solution. The test method is to use pure solutions of various suspicious substances as specimens for separate determination. If a color reaction occurs, this indicates that the method is not highly specific. If the substance to be tested is mixed into the suspect substance for sample measurement, the reaction between the substance to be tested and the reagent is changed, which is interference. For this reason, it is necessary to further improve the method, or set up blank samples, or properly treat the samples to remove interferences, or add appropriate interference masking agents, etc. to improve the specificity of the method.

The temperature and time of the reaction are that some colored substances can react quickly to form, and some colored substances can take a long time to complete the reaction. Increasing the reaction temperature can speed up the chemical reaction and shorten the reaction time. Therefore, if the colorimetry is performed at inappropriate temperature and time, it will cause considerable error. This can be made to react at different temperatures (such as 25 ° C, 30 ° C, 37 ° C), and the end time of each reaction can be observed by detecting the absorbance (generally, the end point of the reaction is reached, and the absorbance subsequently measured will not change). Determine the optimal reaction temperature and time for clinical application.

Stability test The stability of the colored matter produced by the test substance through the color reaction is related to the reliability of the measurement result. Although some colored substances are generated quickly, they are not stable. The color will gradually fade or change after being placed. Although some interfering substances cannot react with the measured substance at the same time, they can slowly interact with the substance after being placed for a period of time. The reagent develops color, making the solution darker. Therefore, it is necessary to perform stability tests while the method is being established. The test method is to use the test specimen, standard solution, and blank solution to perform the color reaction according to the requirements of the method, and then leave it at room temperature for different times to measure its absorbance, and determine the stable time range of the method according to its absorbance change. Generally, colored solutions are required to be stable for more than two hours to meet the needs of clinical applications. If necessary, indicate it.