Do You Know The Detection  Principle Of The Urine Analyzer?

Do You Know The Detection Principle Of The Urine Analyzer?

Do you know the detection principle of the urine analyzer?

内页1What does a urine analyzer do? Do you know its detection principle? The editor tells you the detection principle of the urine analyzer.

Speaking of urine analyzer, it is actually an automated instrument for determining certain specific chemical components in urine. It is widely used in hospital laboratories in medicine and is an important tool for automated urine inspection. It has the advantages of simple and fast operation.

Generally speaking, the urine analyzer is controlled by a microcomputer, and the color change on the test strip is measured by means of a spherical analyzer receiving dual-wavelength reflected light for semi-quantitative determination.

There are several reagent pads containing various reagents on the reagent strip, each of which reacts independently with the corresponding components in the urine, and displays different colors, the depth of the color is proportional to a certain component in the urine, and there is another ” Compensation pad”, as the urine background color, compensates for the errors caused by colored urine and instrument changes.

During use, put the reagent strip with urine adsorbed in the colorimetric tank of the instrument, and the various reagent pads that have produced chemical reactions on the reagent strip are irradiated by the light source, and the reflected light is received by the spherical analyzer. The photocell is irradiated with reflected dual-wavelength light (measurement light passing through the filter and a reference light), and the selection of each wavelength is determined by the detection item.

The urine analyzer will automatically calculate the reflectance according to the following formula [R(%)=Tm.Cs/TsCm×100%], and then compare it with the standard curve, and automatically find and print the corresponding results of various components. If the content of these components is high, the reflected light of the corresponding reagent pad will be darker, otherwise it will be stronger.

According to different working methods, this product can be divided into wet urine analyzer and dry urine analyzer. Among them, the dry urine analyzer is mainly used to automatically evaluate the determination results of the dry test paper method. Because of its simple structure and convenient use, it is widely used in clinical practice.

内页2Result analysis

Because the principles of the two test methods are different, and the factors that affect them are also different, the results of the two test methods are different to some extent.

1. False positives. That is, the occult blood reaction of the urine analyzer is positive and the microscopic examination is negative. The common reasons are:

(1) Hemoglobin (Hb) The occult blood reaction of the urine analyzer can produce a positive reaction not only with the intact RBC, but also with the Hb released by the dissolution of the RBC, while the microscope can only detect the undissolved RBC in the urine. The content of Hb in the urine of healthy people is very small, and it is qualitatively negative. In disease, there are two sources of Hb in urine: one is intravascular hemolysis, plasma Hb exceeds the binding capacity of haptoglobin, and free Hb is excreted from urine. Another is urinary tract (especially upper urinary tract) bleeding, where RBCs disrupt Hb escape when hypertonic or (and) hypotonic. At this time, the occult blood reaction of the urine analyzer was positive, but no RBC or only RBC fragments were seen in the urine sediment microscope.

(2) Myoglobin (Mb) molecule also contains heme group and has peroxidase activity. Mb mainly exists in myocardial and skeletal muscle tissue, and the content of normal human urine is very small and cannot be detected. When the myocardial or skeletal muscle is seriously damaged, the plasma Mb increases, which is excreted by the kidneys, so that the urine Mb content increases, so the occult blood reaction is positive, and the microscopic RBC is negative.

(3) The urine of some patients contains heat-labile enzymes, which can also cause the color of the reagent block to change, the occult blood reaction is positive, and the microscopic examination is negative.

(4) Certain oxidative contaminants, such as hypochlorite, can cause false-positive occult blood reactions.

内页4(5) Bacteriuria Urine is a good culture medium for bacteria. In bacteriuria, some bacteria will produce oxidative substances, which will change the color of the reagent block, resulting in a positive occult blood reaction and a negative RBC test by microscopy. In addition, the invasion of microbial peroxidase can also cause false positives.

(6) Long-term storage and high temperature experiments have proved that the samples are not fresh, stored for a long time or stored at high temperature, so that the positive rate of occult blood reaction is relatively increased, while the RBC microscopic examination is correspondingly reduced, and the test results are very likely to be false positive. Therefore, it is recommended that the storage time of urine samples should not exceed 4 hours.

(7) The overdue use or contamination of urine test strips, as well as improper storage and incorrect operation methods, can cause false positive test results.

(8) The sensitivity of the urine analyzer is too high (++ appears at 0.2mg/dl), and the “gradation” range is too large (+++ at the level of 0.8-50mg/dl). It is often encountered that the instrument test is ++, while the mirror The red blood cell test was negative, and no clinical cause of hemoglobinuria could be found.

2. False negative. That is, the microscopic examination is positive, and the urine analyzer occult blood reaction is negative. The common reasons are:

(1) Influence of food or drugs: When the urine is alkaline due to diet or drugs, RBC dissolves and ruptures, forming brown particles, the occult blood reaction is positive, but the microscopic examination is negative.

(2) When a large amount of VitC exists in the urine, it can compete for the oxygen generated by the reaction, causing a false negative reaction.

(3) High specific gravity and high protein urine samples reduce the sensitivity of the occult blood reaction of the reagent block, making the occult blood reaction false negative.

(4) The mucus composition in urine increases, so that RBCs are wrapped, the reagents cannot contact Hb, and the occult blood reaction is false negative.

3. The effect of centrifugation on the results. If the speed of centrifugation is too fast, the formed components can be destroyed; but if the speed is too slow, when the RBC per milliliter of urine is below 5000, RBC may not be found in the sediment, so that occult glomerulonephritis may be missed. Therefore, when there is doubt about the test results, it can be confirmed by occult blood reaction.

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  • Post time: Jun-21-2022