Understanding Urine Tests

Introduction

Urine analyzer, also known as dry chemical urine analyzer, is an automated instrument that uses photoelectric colorimetric analysis technology to determine certain chemical components in urine. Urine analysis is mainly used for in vitro diagnosis. As one of the "three major routines" of clinical testing projects, it is an important tool for automated urine testing in medical laboratories. This instrument has the advantages of simple operation and fast speed.

Structural composition

Urine analyzer is generally composed of mechanical system, optical system, circuit control system, analysis and processing software, display and printing system.

Mechanical system: Its main function is to transfer the urine test strip to be tested to the detection position, and after the test is completed, the urine test strip is sent to the waste box or removed manually. Optical system: It is usually composed of a light source and a detector. The light source shines on the reagent area of the urine test strip to form reflected light. The analyzer receives the reflected light through the detector and converts the optical signal into an electrical signal. Circuit control system: The main function is to control the operation of each system module of the analyzer. Analysis and processing software: The main function is to analyze the test data and process the user's operation settings. Display and printing system: The main function is to display the operation interface, print and display the test results.

Detection principle

Detection principle of urine dry chemical test strip

The detection of urine dry chemical test strip is based on the principle of photoelectric colorimetry. Through the color change produced by the reaction between the reagent area on the urine test strip and the biochemical components in the urine, the content of biochemical components in the urine is determined. The items that can be detected include urine white blood cells, urine occult blood, urine protein, urine sugar, urine nitrite, urine ketone bodies, urobilinogen, urine bilirubin, urine specific gravity, urine pH, vitamin C, creatinine, urine calcium, trace albumin, etc.

When the test strip soaked with urine sample is placed on the conveyor, the conveyor of the instrument conveys the test strip to the bottom of the detector. After the reagent blocks on the test strip that have produced chemical reactions are irradiated by the light source, their reflected light is received by the detector. Each reagent block in the test strip reacts independently with the corresponding component in the urine, showing different colors, and the depth of the color is proportional to a certain component in the urine. The darker the color of each reagent block after reaction, the greater the absorption light value, the smaller the reflected light value, and the smaller the reflectivity. Conversely, the lighter the color, the smaller the absorption light value, the greater the reflected light value, and the greater the reflectivity. In other words, the depth of the color is proportional to the concentration of various components in the urine sample.

There is also a blank block in the test strip to compensate for the errors caused by urine color and instrument changes. The light value of the reflected light in each reagent area measured is compared with the reflected light value of the blank block, and the reflectivity is calculated by calculation. The instrument determines the content of biochemical components in urine based on the reflectivity.

Principle of urine specific gravity detection

The urine specific gravity detection method adopts the refractometer method, which uses the correlation between the refractive index of light and the total solid content in the solution for determination. The refractometer method can be used in the temperature range of 15℃ to 38℃, and can be adjusted by the temperature compensation device before use; it can be calibrated with a known standard high specific gravity concentration solution and a standard low specific gravity deionized water. It is easy to standardize and requires less specimens, especially suitable for oliguric patients and pediatric patients.

The principle of urine specific gravity detection is based on the principle that urine of different concentrations has different refractive indices. That is, monochromatic parallel light of the same wavelength is applied to a prism containing the urine to be tested, and the specific gravity value is calculated based on the different positions of the refracted light hitting the photoelectric technology detector (displacement sensor). The block diagram of the urine specific gravity detection principle is shown in the figure below.

Principle of urine turbidity detection

The urine turbidity module emits light, passes it through a sample, and detects how much light is scattered by particles in the water from a direction 90° to the incident light (the most stable scattered light angle is at right angles to the center line of the incident light. Measuring scattered light at 90° can minimize the effect of particle size on scattered light intensity). This scattered light measurement method is called scattering method.

Classification

(1) Semi-automatic urine analyzer

The composition of a semi-automatic urine analyzer generally includes a test strip conveyor, a light source, a monochromatic processor, a photoelectric converter, a central processor, an analysis and processing software, and a display and printing device. The block diagram of its working principle is as follows:

The semi-automatic urine analyzer has a low degree of automation. The operator needs to manually soak the urine test strip with the sample, filter out the excess urine sample, and then put the urine test strip on the test strip transmission device on the analyzer, and finally the analyzer will automatically detect it. The semi-automatic urine analyzer requires the operator to be on duty next to the instrument to operate it, which takes up manpower and has low work efficiency. In addition, there is a high probability that the test results will fluctuate due to human operation errors.

(2) Fully automatic urine analyzer

The fully automatic urine analyzer generally includes an automatic sample injection device, an automatic strip selection device, a test strip transmission device, a liquid circuit device, a light source, a monochrome processing, a photoelectric conversion, a central processing unit, a waste collection device, an analysis and processing software, and a display and printing device.

The fully automatic urine analyzer has an automatic sample introduction device, a liquid path device and an automatic strip selection device. The operator only needs to put the test tube containing the urine sample into the automatic sample introduction device and click the start button. The instrument can automatically complete the batch urine dry chemical test. The operator does not need to contact the sample and urine test strips for a second time, and can achieve full off-machine operation, freeing up manpower, improving work efficiency, and reducing the probability of fluctuations in test results due to human operation errors.

(3) Test strips

The strips currently used in the Chinese market mainly include 8 items, 9 items, 10 items, 11 items, 12 items, 13 items, and 14 items. The items that can be detected include urine pH, urine white blood cells, urine nitrite, urine protein, urine sugar, urine ketones, urobilinogen, urine bilirubin, urine specific gravity, urine red blood cells, creatinine, vitamin C, urine calcium, microalbumin, etc.

Conclusion

In addition to clinical applications, urine analyzers are also widely used in the field of health monitoring. For example, in personal health management, urine analyzers can be used to monitor health conditions and detect potential health problems in a timely manner. By regularly measuring chemical indicators in urine, individuals can understand their physical condition so that they can make corresponding adjustments and interventions. In addition, urine analyzers are also widely used in fields such as athlete health monitoring and drug testing.

In scientific research, urine analyzers also play an important role. Urine analyzers can help researchers conduct rapid and accurate analysis of urine samples. In biomedical research, urine analyzers can be used to study metabolic diseases, urinary system diseases, kidney diseases, etc. By measuring different components in urine, the pathogenesis of these diseases can be explored, providing important scientific basis for the development of new drugs and the improvement of treatment methods.

The development and application of urine analyzers are inseparable from technological progress and research innovation. At present, with the continuous development of science and technology, urine analyzers are developing in the direction of being more portable, highly sensitive and highly accurate. At the same time, with the development of data analysis technology, urine analyzers will also be combined with technologies such as big data and artificial intelligence to achieve more intelligent analysis and interpretation.

This will further enhance the application value of urine analyzers and promote their widespread application in medical treatment, health monitoring and scientific research.