Urine sugar tests mainly detects glucose in urine, which can serve as a reference for diagnosing diabetes, and is also the simplest and most commonly used method for patients to monitor their own condition.
1.Qualitative urine sugar tests.
(I) The Benedict’s reagent method
The Benedict’s reagent method is still the most widely used method in hospitals, which is the reduction method with copper sulfate, such as Benedict’s reagent for urine sugar test. Its basic principle is the same as the Folin-Wu method for blood sugar measurement. The specific operation is to use a pipette to suck up Benedict’s reagent, add 20 drops into a test tube, then add 2 drops of urine and mix well, boil for 1 minute with an alcohol lamp, and observe the color change to evaluate the negative or positive urine sugar. The criteria for the qualitative evaluation of urine sugar by the Benedict method are as follows:
| Color | Unchanged | green | turbid green | earthy yellow | orange | brick red |
| Qualitative | – | ± | + | ++ | +++ | ++++ |
| Quantitative | <0.1 | <5 | 5 | 5-10 | 10-15 | 20 |
(2) Urine sugar test strip method:
It should be noted that the current commercially available urine sugar test strips use the principle of glucose oxidase method. Urine sugar test strips are simple, convenient, accurate, and relatively low-cost, making them a good means for diabetic patients to monitor their condition and should be widely promoted and applied. Normal individuals should have a negative urine sugar qualitative test at any time. When blood glucose exceeds 8.9-10mmol/L, urine sugar can become positive, and generally, in elderly patients, urine sugar becomes positive when blood glucose exceeds 11.1mmol/L.
(3) Precautions for urine sugar qualitative examination:
Benedict’s reagent method can produce false-positive results due to the presence of fructose, lactose, pentose, uric acid, and vitamin C. Lactate diabetes can occur during pregnancy and breastfeeding, and renal diabetes can occur with kidney disease. Other factors to consider include stress-induced diabetes and nutritive diabetes.
2.Urine sugar quantification:
Mainly measures 24-hour urine sugar quantification. Some patients require measurement of four-stage urine sugar quantification. When collecting samples, 5-20ml of xylene is added to the container after the first urine flow to act as a preservative, preventing bacterial proliferation and decomposition of glucose, which could affect the test results.
Normal individuals excrete small amounts of sugar in urine, less than 100mg per day. Diabetic patients excrete large amounts of glucose in urine, with most patients excreting less than 100g. In China, the highest 24-hour urine sugar quantification reported was 636g, and some Americans have reported values exceeding 1000g.
Guidelines from American Association for Clinical Chemistry
The American Association for Clinical Chemistry (AACC) provides guidelines and recommendations for various laboratory tests, including urine glucose testing. Here are some key points regarding urine glucose testing methods as outlined by the AACC:
- Test Principle: Urine glucose testing is based on the detection of glucose in urine samples. Common methods include glucose oxidase or glucose dehydrogenase reactions that produce a measurable signal, such as a color change or fluorescence, which can be quantified.
- Test Strip Method: One of the most common methods for urine glucose testing is the use of test strips. These strips contain reagents that react with glucose in the urine, changing color depending on the concentration of glucose present. The color change is then compared to a color chart or measured with a reflectance meter to determine the glucose level.
- Laboratory-based Methods: In clinical laboratories, more sophisticated methods may be used, such as enzymatic assays or high-performance liquid chromatography (HPLC), which provide more precise and accurate quantification of urine glucose levels.
- Interpretation of Results: The AACC emphasizes that the presence of glucose in the urine should be interpreted with caution and in the context of the patient’s clinical status. Persistent glycosuria is generally considered abnormal and may indicate diabetes or other conditions affecting glucose metabolism.
- Quality Control and Assurance: The AACC recommends strict quality control measures to ensure the accuracy and reliability of urine glucose testing. This includes regular calibration of instruments, use of control materials, and adherence to standard operating procedures.
- Clinical Utility: Urine glucose testing is useful for screening and monitoring diabetes, as well as detecting conditions that may cause hyperglycemia. However, it is important to correlate urine glucose results with blood glucose measurements for a comprehensive assessment.
These guidelines help ensure that urine glucose testing is performed and interpreted correctly, contributing to accurate diagnosis and management of diabetes and other metabolic conditions.
