How Do I Interpret My Urinalysis Results?

Urine analyzer is an automated instrument for measuring certain chemical components in urine. It is an important tool for automated urine testing in medical laboratories. It has the advantages of simple and fast operation. Under the control of the computer, the instrument collects and analyzes the color information of various reagent blocks on the test strip, and after a series of signal conversions, it finally outputs the measured chemical content in urine.

Chinese name: Urine analyzer
Foreign name: Urine Analyzer

Category Name: Chemical urine analysis instrument
Management category: Class II medical devices

Basic structure of urine analyzer

Urine analyzer is generally composed of test strip, mechanical system, optical system, circuit system, input and output system, etc. ^[1] .

Test strip

There are several reagent pads containing various reagents on the test strip, each of which can independently react with the corresponding components in the urine to show different colors, and the depth of the color is proportional to the measured components in the urine. Different types of urine chemical analyzers are developed with matching test strips suitable for their own use. The test strip adopts a multilayer film structure: the first layer of nylon film protects the reaction to prevent pollution of macromolecular substances and ensure the integrity of the test strip; the second layer of fleece layer includes the periodate area (some reagents The module contains this area) and the reagent area. The periodate area can destroy the interfering substances of vitamin C. The reagent area contains reagent components, which mainly undergo chemical changes with the components to be measured in urine, resulting in a color change; the third layer is a water-absorbing layer, which can Make the urine infiltrate uniformly and quickly, and can inhibit the flow of urine to the adjacent reaction area; the last layer of plastic sheet serves as a support). Each reagent block reacts with the component to be measured in urine and presents different colors. Usually, the test block contains one more blank block than the analyzer test item. In order to eliminate the test error caused by the uneven color of the urine itself and the state of the reagent block distribution, the measurement accuracy is improved.

Mechanical system

The main function of the mechanical system is to transfer the test strip to be tested and the specimen to be tested to the testing area. After the analyzer detects the test strip, it is discharged to the waste box. Different types of instruments use different mechanical devices, such as gear combinations, transfer tapes, robotic arms, sample needles, sample mixers, etc.

Optical system

The optical system generally includes three parts: light source, monochrome processor and photoelectric conversion. The light irradiates the surface of the reactant to generate reflected light, and the intensity of the reflected light is proportional to the reaction color of each item. The reflected light of different intensity is converted into an electric signal by a photoelectric converter and sent to an amplifier for processing.

There are usually three types of optical systems for urine analyzers: light-emitting diode (LED) systems, filter spectroscopic systems, and charge-coupled device (CCD) systems.

Circuit system

The circuit system amplifies the converted electric signal, sends it to the central processing unit (CPU) for processing after analog-to-digital conversion, calculates the final test result, and then outputs the result to the screen display and sends it to the printer for printing. The role of the CPU is not only responsible for the processing of detection data, but also to control the organic operation of the entire mechanical system and optical system, and to achieve a variety of functions through software.

5. Input and output system

It consists of display, panel, printer and other components. It is used by the operator to input specimen information, observe the working status of the instrument, and print reports.

How a urine analyzer works

The essence of the urine analyzer test principle is the absorption and reflection of light. The liquid sample is directly added to the multiple reagent strips which have been cured with different reagents. The corresponding chemical components in the urine cause the modules on the multiple reagent strips to contain various special reagents to change color. The color depth and the specific chemistry in the urine sample The component concentration is directly proportional; the multi-test strip is placed in the colorimetric sampling slot of the urine analyzer. Each module is sequentially illuminated by the light source of the instrument and generates different reflected light. The instrument receives light signals of different intensities and converts them into corresponding ones. The electrical signal is calculated by the microprocessor (CPU) for the reflectance of each test item, then compared with the standard curve to be corrected to the measured value, and finally the result is automatically printed in a qualitative or semi-quantitative manner ^[1] .

Such instruments are generally controlled by a computer, and the ball area spectrometer is used to measure the color change on the test strip in a manner that accepts dual-wavelength reflected light for semi-quantitative determination. There are several reagent pads containing various reagents on the reagent strip, each of which independently reacts with the corresponding component in the urine, and displays different colors. The depth of the color is proportional to a certain component in the urine. There is another " "Compensation pad", as the background color of urine, compensates for errors caused by colored urine and instrument changes.

Place the reagent strip with the urine absorbed in the colorimetric tank of the instrument. The various reagent pads on the reagent strip that have generated a chemical reaction are illuminated by the light source, and the reflected light is received by the ball area analyzer, and the photocell of the ball area analyzer is reflected Dual-wavelength light (measurement light passing through the filter and a beam of reference light) is irradiated, and the choice of each wavelength is determined by the detection item.

The instrument usually calculates the reflectance automatically according to the following formula, and then compares it with the standard curve to automatically find the corresponding results of various components. The content of a certain component in urine is high, and the reflected light of its corresponding reagent pad is dark, otherwise it is stronger. .

Reflectivity Fraction: R (%) = Tm.Cs / TsCm × 100%

In the formula, R (%) is the reflectance; Tm is the reflection intensity of the reagent pad to the measured wavelength; Ts is the reflection intensity of the reagent pad to the reference wavelength; Cm is the reflection intensity of the calibration pad to measure the length of the defect; The reflection intensity at the reference wavelength.

Clinical application of urine analyzer

The significance of urinalysis is that by understanding the physiological functions and pathological changes of the urinary system, it can indirectly reflect the functions of multiple organs and systems throughout the body ^[2] .

Diagnosis and observation of urinary system: such as inflammation, tuberculosis, stones, tumors.
Assist in the diagnosis of other systemic diseases: such as diabetes, pancreatitis, jaundice, heavy metal poisoning, Cushing's disease, and pheochromocytoma.
Safe medication monitoring.
Diagnosis of obstetric and gynecological disorders: such as pregnancy, chorionic carcinoma, hydatidiform mole.

Urine analyzer classification

1. Classified by working method:

Wet urine analyzer and dry urine analyzer. Among them, the dry urine analyzer is widely used in clinic because of its simple structure and convenient use ^[2] .

2. Classified by test items:

(1) 8 urine analyzers: detection items include urine protein (PRO), urine sugar (GLU), urine pH, urine ketone body (KET), urinary bilirubin (BIL), urobilinogen (URO), occult blood (BLD), urine nitrite (NIT).

(2) 9 items of urine analyzer: 8 items + urine white blood cells (LEU).

(3) 10 items of urine analyzer: 9 items + urine specific gravity (SG).

(4) 11 items of urine analyzer: 10 items + vitamin C.

(5) 12 items of urine analyzer: 11 items + color or turbidity.

3. Classified by degree of automation:

(1) Semi-automatic urine analyzer: According to its detection items, it can be divided into 8 items of urine, 9 items of urine, 10 items of urine, 11 items of urine, and 12 items of urine.

(2) Fully automated urine analyzer: According to its detection items, it can be divided into 10 items of urine, 11 items of urine, and 12 items of urine.

Detection method of urine analyzer

Urine pH check

The results have two meanings: reflect the acid-base metabolism status in the body; because the principle of determination of urine protein and urine specific density is based on the color change of the last PH reagent on the module, therefore analyzing pH changes and monitoring urine pH changes on other module areas Disturbing effects of the reaction.

2. Urine specific test

Suspension method and refractometer method have been used to determine urine specific density. The main method is to measure the concentration of solids in urine. With the advent of 10 urine analyzers, the test strip method has been widely used to determine the specific density of urine. Its membrane mainly contains polymer. Electrolyte (methacrylic acid) and acid-base indicator and buffer. This is the acid brick indicator method, which is based on the principle of Pka passing through polyelectrolyte and related to urine ion concentration. The polyelectrolyte in the narcotic strip contains acidic groups that dissociate with the high concentration in the urine sample. The more ions, the more acidic groups dissociate and change the pH in the module. This change can be changed by the membrane block. The color change of the acid-base indicator in the indicator is displayed, and then converted into the specific density of urine.

Urine protein test

The urine protein determination of the urine analyzer is based on the principle of indicator protein error. The membrane block mainly contains the acid-base indicator Zao bromophenol blue, the citrate buffer system and the active agent of the south. At pH 3.2, the anion produced by bromophenol changes color after binding to the cation-containing protein (albumin). Dry chemical method for determination of urinary protein is simple and fast, but when using it, you should pay attention to: When patients take strong alkaline urine caused by drugs such as quinine and sulfadiazine, `` will cause false positive results of dry chemical method and The result is a false negative result. Dilute acetic acid can be used to adjust the pH of the urine by 5-7 `` re-experiments '' to distinguish whether a false positive is caused by strong alkaline urine. Studies have proven that dozens of drugs can make urine protein test False positive `` Some scholars tested urine protein before and after administration of patients with large doses of penicillin ''. The results showed that: 2.5 million unit groups for 2 hours, 3.2 million units for 3 hours, and 4.8 million units for 5 hours. False positive for sulfosalicylic acid and false negative for dry chemistry. Different assays have different sensitivities to the detection of different types of proteins in the urine of patients. Biuret quantification can show sensitivity to albumin and globulin, while the sensitivity of dry chemical measurement of globulin is only 1 / 100- of albumin. 1/50. Therefore, for patients with kidney disease, especially those who need to observe the urine protein content systematically during the development of the disease, the sulfosalicylic acid method (or heating acetic acid method) qualitative and biuret method should be used for quantitative tests. When the specimen contains other secretions (such as reproductive system secretions) or contains more cellular components, it can cause false positives. It is suggested to use the sulfosalicylic weight method as the reference method for dry chemical detection of urine protein.

4. Urine glucose measurement

The urine test strip method is used to measure urinary glucose using an enzyme method. Its membrane contains glucose oxidase, peroxidase and chromogen. There are two main types of color sources used by different manufacturers: using potassium iodide as the chromogen, the positive reaction is red; using o-benzidine as the chromogen, the positive reaction is blue. The determination of the original amount is the oxidation of glucose to glucuronic acid and hydrogen peroxide by the glucose oxidase, which is then released by the catalysis of the peroxidase to make the chromogen color. This method is most commonly used. The urine test strip method should be used with caution: The urine test strip method is different from the Bannwick qualitative method in that the former is highly specific and absorbs glucose and reacts with the latter; the latter has antigenic sugar and all reducing properties in the urine. Substances react, so specimens that are negative in the urine test strip method may have positive results in the Bansted method; The dry chemical method is different from the Bansted method in that the sensitivity of the dry chemical method is high, and the glucose content is 1.67-2.78mmol Weak positive at / L; Weak positive at 8.33mmol / L by Banstedt method; Interfering substances have different effects on the two methods: Urine contains reducing substances with strong affinity for oxygen that can be compared with Banstedt method The copper ion in the reaction produces false positive, but it can reduce the color of H2O2 produced by the dry chemical test strip and make it false negative. The method of elimination is to boil urine for a few minutes to destroy vitamin C before carrying out the experiment. Existing test strips containing vitamin C oxidase can eliminate this interference. The dry chemical method for measuring urinary glucose is only a general semi-quantitative test. It is designed to have a concentration level different from that of traditional Banche. The two are comparable; therefore, for the dynamic observation of diabetes, a positive result appears in dry chemistry. It is best to use wet chemical quantification methods to establish an accurate urinary glucose range or to collect diurnal urine samples for urinary glucose quantification.

5. Urine ketone body test

The membrane of urine ketone body mainly contains sodium nitrosoferricyanide, or reacts with acetoacetic acid and acetone in the urine to produce purple. Its sensitivity to acetoacetic acid is 50-100mg / L and acetone is 400-700mg / L, it does not react with -hydroxybutyric acid. Please pay attention to it during use: Because both acetone and acetoacetate in the ketone body of urine are volatile, acetoacetate is more easily decomposed into acetone by heat; when the urine is contaminated by bacteria, the ketone body disappears, so the urine must be fresh and promptly submitted for inspection. In order to avoid false negative results or low results due to volatilization or decomposition of ketone bodies; Sensitivity of dry method and ketone powder method are different: the sensitivity of ketone powder method to acetoacetic acid and acetone is 80mg / L and 100mg / L. It is not as sensitive as the test strip method, so there may be differences in results between the two methods of the same pathological specimen, and special attention should be paid when analyzing the results; ketosis caused by different etiologies, the composition of ketone bodies is different, even a patient may have different course of disease, For example, in the nomenclature of early stages of diabetic ketoacidosis, -hydroxybutyric acid, the main ketone body component, has little or no acetoacetic acid. At this time, the measurement result can lead to an underestimation of the total ketone body amount. After the symptoms of diabetic ketoacidosis are alleviated, -hydroxybutyric acid is converted to acetoacetic acid, and the content of acetoacetic acid is increased from the initial acute stage, which is likely to overestimate the condition. Therefore, the inspector must pay attention to the development of the disease course and analyze the experimental results with the clinician.

6. Urinary bilirubin, urobilinogen examination

The principle of urinary bilirubin determination is to combine bilirubin in a strongly acidic medium with a coupling reaction of 2,4-dichloroaniline diazonium salt to become purple. The principle of urinary bilirubin measurement is the same as the modified Ehrlich method. The main points of the two methods are: The specimen must be fresh to prevent bilirubin from becoming bilirubin under sunlight; urobilinogen is oxidized to urobilin. When urine contains high concentrations of vitamin C and nitrite, inhibiting the azo response makes urine bilirubin false-negative. It can be false positive when the patient receives a large amount of chlorpromazine treatment or the metabolism of phenylazopyridine hydrochloride in urine. Some endogenous substances in urine such as bilirubin, indole, bilirubin, etc. can make urobilinogen test results positive, and some drugs can produce color to interfere with the experiment. The urinary biliary excretion of normal people fluctuates greatly every day, and the amount is small at night and in the morning, and it increases rapidly in the afternoon, reaching the highest peak at 2-4 noon; meanwhile, the clearance rate of urobilinogen is related to urine pH, pH 5.0 , The clearance rate is 2ml / min; increased to 25ml / min at Ph8.0, so some scholars advocate using sodium ammonium carbonate in advance to patients to alkalinize urine and slowly collect urine at 2-4pm (2 hours discharge) Measurements were performed to improve the detection rate.

7. Urine Nitrite Test

The membrane block mainly contains p-aminophenylarsenic acid and 1,2,3,4-tetrahydroxy-p-quinolinol-3 phenol. Most of the time when urinary tract infections are caused by Escherichia coli, normal people's urine contains nitrate from food or protein metabolism, and when pooled urine has Escherichia coli infection, the nitrate is reduced to nitrite. Salt, which can diazotize the p-ammonia-based phenylarsenic acid in the membrane to form a diazonium salt, which is coupled with 1,2,3,4-tetrahydroxy-p-quinoline-3 whip to make the membrane red. In order to diagnose whether the patient is infected with Escherichia coli, the detection sensitivity is 0.03-0.06g / l. The detection rate of nitrite in urine is affected by whether the infected bacteria contain nitrate reductase, whether the food contains nitrate, and whether the urine specimen stays in the bladder for more than 4 hours, which meets the above three conditions. The detection rate of the test is 80%, otherwise it can show negative results. Therefore, the negative test of this test cannot rule out the possibility of bacterial urine, and a positive nitrite test can not completely confirm the urinary system infection. The specimen may be false positive if it is left for a long time or contaminated. It should be combined with other urine analysis results to obtain a comprehensive analysis. Right judgment.

8. Urine leukocyte examination

The principle of urinary leukocyte detection based on urine test strips is based on the neutrophil cytoplasm containing specific esterases, which can act on the indoxyl esters in the membrane block. It reacts with the diazonium salt to form a purple condensate. Its color The depth is proportional to the number of neutrophils. Attention should be paid to the operation: The urine specimen must be fresh, and it should be measured immediately after urine retention, so as not to cause bad leukocyte damage, which will cause artificial experimental errors between the dry chemical method and the microscopy method; Monocyte and lymphocyte reactions. When renal transplant patients have rejection reactions, lymphocyte-based or other causes of monocytes in urine will produce negative results in urine; urine contaminated with formaldehyde or contains When high concentrations of bilirubin or certain drugs are used, Ji produces false positives; when urine protein is greater than 5 g / L or urine contains a large amount of vanillin and other reds, the results may be low or false results may occur. Since the principle of the white blood cell detection of the urine analyzer is very different from the counting experiment under a microscope, its reporting method is also two different concepts. It is difficult to find the correspondence between the two. So far, there is no direct conversion method. Inspection is only a screening test and must not replace microscopy.

9. Urine hemoglobin, urinary red blood cell examination

The membrane block mainly contains two substances, solanin hydroperoxide or cobalt dihydrogen peroxide, and chromogen (such as o-benzidine). The principle is that the hemoglobin in the red blood cells in the urine or the hemoglobin released by the destruction of the hemoglobin has catalase-like activity, which can decompose the solanin hydroperoxide or cobalt perhydrogen peroxide, which can oxidize the relevant chromogen. (Such as o-benzidine) to make it color. When using the urine test strip method to check the urine redness, you should pay attention to: Because the sensitivity of the reagent strips of different manufacturers or different models is different, you must pay attention to the difference between batches; The dry chemical method can be used with the intact red blood cells. Free hemoglobin response, so you must understand the clinical diagnosis and comprehensive analysis when reporting. Because red blood cells in terminal urine of patients with kidney disease can be deformed and lysed due to various factors, hemoglobin can escape, which can lead to differences between instrumental methods and hydrometric methods; Thermal enzymes, myoglobin, or bacteriuria contained in urine can cause false positives ; A large amount of vitamin C can interfere with the test results and cause some test strips to produce false negatives, so you should be vigilant

Analysis of urine analyzer results

Different interference factors have different effects on the density results of the above three methods:

The first is that when the non-ionic compounds in the urine increase, the specific density measured by the suspension method and the refractometer method can be higher, while the test strip method is only related to the ion concentration and is not affected by it;

The second is that when the protein in the urine increases, all three methods have different degrees of increase, the most obvious is the test strip method, followed by the refractometer method;

The third is that the test strip method is susceptible to pH. When the urine pH is> 7, the measurement result should be increased by 0.005 as compensation for the loss of urine pH.

How to use a urine analyzer

Take the semi-automatic instrument as an example:

Turn on the power of the instrument, observe whether the instrument is abnormal, and warm up for several minutes.
Select the required test strip access.
Put the quality control test tape (random accessories) into the test slot, and start the run key. The instrument will print out the quality control result in a moment, and it should be compared with the standard value on the test tape box. Take out the quality control tape and store it. If the instrument fails, the word ROUBLE will be printed out. Follow the prompts to find the corresponding fault table and remove the fault.
The test strip to be tested is immersed in a random urine specimen, and the immersion time is performed according to the test strip instructions. When removing, the lower end of the test strip should be close to the inner wall of the specimen cup to remove excess urine.
Put the test strip into the test slot within the specified time and observe the print result ^[3] .

Cautions for Urine Analyzers

Keep the instrument clean and use a clean sampling cup.
Freshly mixed urine is used. After the specimen is collected, it should be tested within 2 hours.
Different types of urine chemical analyzers use different urine test strips. When the test strip changes from refrigerated temperature to room temperature, do not open the lid of the test strip. The cap should be capped immediately after each use to prevent the test strip from getting wet.
The test strip is immersed in urine for 2 seconds. Excess urine samples should be sucked off with filter paper. All reagent blocks, including blank blocks, must penetrate the urine.
The optimum temperature of the instrument should be 20-25 at room temperature. Urine samples and test strips should also be maintained within this temperature range.
When reporting the test results, because the different grades of urine chemical analysis are only designed to differ greatly in the grade of the results, they cannot be interpreted by symbolic code results alone. The analysis should be performed in combination with semi-quantitative values, so as not to report the qualitative results properly Clinical interpretation brings confusion.
Test strips should be stored in dry, opaque, covered containers, and stored in a cool, dry place. Do not put them in the refrigerator or expose them to volatile fumes.

Urine Analyzer Maintenance and Care

Urine chemical analyzer is a precise electronic optical instrument, which must be carefully maintained. The instrument should avoid prolonged sunlight exposure, excessive temperature and excessive humidity. Irregular operation of the instrument will disrupt the normal operation of the instrument and cause bad results ^[3] .

Routine maintenance

Before operation, you should carefully read the instructions of the urine chemical analyzer and the instructions of the urine test strip; each urine chemical analyzer should establish an operating procedure and operate according to its regulations.
A special person should be responsible for and establish a dedicated instrument notebook, and register the situation, problems, and maintenance of the Tianqi paddle.
Before the daily test, the instrument should be thoroughly inspected (various devices and waste liquid devices, the condition of the printing paper, and whether the instrument needs to be calibrated, etc.) and it can be turned on after confirming five errors. After the test, the instrument must be cleaned and maintained thoroughly.

maintenance

Daily maintenance: It should be cleaned up after use every day and washed with water.
Weekly or monthly maintenance: Various types of urine chemical analyzers should be maintained weekly or monthly according to the specific conditions of the instrument.