Just like the eyes are the windows to the soul, urine is a mirror of kidney disease. By examining urine, doctors can know the type of kidney disease and determine the severity of the disease. Therefore, different urine tests are the most common tests in nephrology, and how to properly collect urine specimens is related to the accuracy and reliability of the tests. However, in the outpatient clinic, due to the large number of patients, doctors rarely have enough time to instruct patients on the specific method of urine retention when issuing lab orders, and urine retention is very arbitrary, which brings great obstacles to the interpretation of lab orders, not only wasting patients’ lab fees and precious time, but even misleading doctors’ judgment on diseases. Today, we will learn the precautions for proper urine specimen retrieval and the main clinical significance of different labs together, hoping to help patients to seek medical treatment smoothly. The urine tests commonly used in nephrology include urine routine + sediment microscopy, urine red blood cell phase, early kidney injury indicators (albumin/creatinine ratio, NAG enzyme, a1 microspheres), urine culture, 24-hour urine examination (urine protein quantification, urine ion quantification, urine acid quantification, urine light chain quantification, creatinine clearance), urine osmolality, urine protein electrophoresis, urine immunofixation electrophoresis, urine routine + sediment microscopy : Retention method: urine routine examination can be morning urine (the first urine in the early morning) or random urine, but all need to retain the middle segment of urine to prevent contamination of the urethra or female vaginal disease, and send fresh urine as soon as possible. The midstream urine mentioned here is the urine that is picked up in a small urine cup during continuous uninterrupted urination. Some female patients who receive urine for testing as soon as they start urinating may have a significant increase in leukocytes and squamous epithelial cells in the urine due to vaginitis contamination of the urine, at which point the mid-stage urine needs to be retested. Clinical significance: Urine routine contains many tests, protein, occult blood, leukocytes, nitrite, glucose, bilirubin, urobilinogen, pH and specific gravity. It may suggest many information, such as nephritis, tubulointerstitial nephropathy, urinary tract infection and liver damage, etc. I would like to highlight that urine occult blood is not equal to hematuria. Many analyzer results show how many red blood cells per microliter of urine, often with decimal points, such as 87.4/μl, and these results are not accurate enough. Hematuria is diagnosed based on microscopic examination of urine sediment, where the number of red blood cells per high magnification field exceeds 3, and is commonly diagnosed in nephritis, stones and tumors. Similarly, leukocyturia is diagnosed only when there are more than 5 white blood cells and is commonly seen in urinary tract infections, interstitial nephritis, etc. Thus, the importance of microscopic examination of urine sediment can be seen as an important test for the diagnosis of kidney diseases. Urine red blood cell phase: This is an important test to distinguish glomerulogenic hematuria from non-glomerulogenic hematuria, which is not available in every hospital because it requires special examination equipment – phase difference microscope. Simply put, it helps to distinguish whether it is nephritis or not. Urine can be collected in the same way as routine urine, and morning urine is preferred. Since this test focuses on cell morphology, it requires a higher degree of freshness in the urine. Patients are encouraged to urinate in the nearest laboratory and send it for testing as soon as possible. Early kidney injury indicators: This test includes tests such as albumin/urine creatinine ratio, NAG enzymes, and a1 microspheres, which assess glomerular and tubular function and are not “early” assessment indicators, as the name suggests. However, microalbuminuria (as reflected by the albumin/urine creatinine ratio) can be seen in the early stages of diabetic nephropathy and hypertensive kidney damage. Urine retention is the same as for routine urination, with morning urine being the best. Urine culture: This is an important test for urinary tract infections. If leukocyte urine is found, this test should be performed to identify the pathogenic bacteria of the infection and to guide the clinical use of medication. To do this test, the patient needs to retain the middle part of the first urine in the early morning, and in the case of women, it is better to clean the vulva with water to prevent contamination of the urine specimen. Since the use of antibiotics may affect the test results, and since the results of the urine culture need to wait for about 7 days, it is recommended that the urine culture be taken first, followed by empirical treatment, and then the treatment plan be adjusted according to the laboratory results. Hourly urine test: Retention method: As the name implies, this is a test that requires the retention of urine for 24 hours throughout the day. In other words, every drop of urine needs to be collected during the day. First prepare a large basin or bucket as a container for urine retention. Patients are usually advised to urinate first at 6:00 am, discard it (this urine can be tested for routine urine, early kidney injury, urine culture, etc. as described above), and leave it from the second urine, leaving each urine inside the same large basin or bucket until 6:00 am the next morning, when another urine is urinated and left. All urine is measured first, and measuring cups are usually available from the laboratory. After the measurement, record the urine volume on the lab sheet, then mix all the urine and leave a small urine tube for testing. If creatinine clearance is required, a tube of blood should be drawn on an empty stomach at the same time as the urine is sent. Clinical significance: The 24-hour urine examination allows the determination of urinary protein, urinary ions, uric acid, urinary light chain, and urinary creatinine, respectively, for the diagnosis and assessment of the efficacy of different diseases. Urine osmolality: This is a test to assess the concentration function of the kidneys and needs to be evaluated together with blood collection for blood osmolality. Patients are often advised not to eat or drink after 10:00 pm the night before the test, until the second urine is passed for this test in the morning of the next test day, and blood is collected on an empty stomach. Only after that can they eat and drink. Urine protein electrophoresis: The method of urine retention is the same as that of urine routine. It is mainly used to analyze the assessment of the type of protein in the urine and can detect small molecule proteins of tubular origin, as well as non-selective proteinuria with mainly albumin and large molecule proteins after glomerular lesions. Urine immunofixation electrophoresis: The method of urine retention is the same as that of urine routine. It is mainly used to analyze urine for the presence of specific components of immunoglobulins or their light and heavy chain components, and can assist in the diagnosis of multiple myeloma.