Urinalysis is a non-invasive laboratory test used to evaluate the physical properties, chemical composition, and microscopic structure of urine. Its primary purpose is to assist in diagnosing urinary tract infections, renal diseases, metabolic disorders, and systemic illnesses through abnormal urine indicators. This test is often used as an initial screening tool and, when combined with other imaging or blood tests, can improve diagnostic accuracy.
The testing process involves three stages: first, observing the urine’s color, clarity, and appearance; second, using chemical test strips to measure pH, protein, or glucose levels; and third, microscopic analysis of cells, crystals, or pathogens. The entire process is quick and cost-effective, making it suitable for routine outpatient screening.
Urinalysis mainly falls into three categories:
The mechanism involves the direct correlation between changes in urine components and disease states. For instance, increased white blood cells are common in urinary tract infections, while hematuria may indicate bleeding within the urinary tract. These biomarkers help clinicians narrow down diagnoses and plan further investigations.
Urinalysis is applicable in various clinical scenarios:
Additionally, this test is suitable for routine health check-ups to detect early, asymptomatic renal lesions or crystallization, thereby preventing stone formation or deterioration of kidney function.
Patients should collect 50-100 mL of midstream clean-catch urine, preferably first-morning urine to increase protein concentration. Before collection, the external genital area should be cleaned to avoid contamination with blood, semen, or secretions. Test strips should be stored in a cool place, and results should be read within 2 hours to prevent oxidation errors.
The laboratory procedures include:
This test offers multiple clinical benefits:
The advantages include early detection of potential issues, such as proteinuria appearing weeks before symptoms, aiding early intervention. For long-term patients, routine monitoring can evaluate treatment effectiveness.
Urinalysis itself carries no biological risks, but false positives or negatives may occur. For example, excessive vitamin C intake can interfere with blood glucose testing, and overly diluted urine may reduce protein detection sensitivity.
Potential errors to watch for include:
Fasting from high-protein foods or vitamin C supplements before testing is recommended to avoid interference. Female patients should avoid urine collection during menstruation to prevent blood contamination, and males should avoid semen contamination. Patients with severe mobility issues may require catheterization, but infection risk should be considered.
Contraindications include:
Urinalysis results should be interpreted alongside blood biochemistry, ultrasound, or estimated glomerular filtration rate (eGFR). For example, positive urine protein should be evaluated with serum creatinine to assess kidney function. The test itself does not directly interact with medications or surgeries.
Special attention should be paid to the effects of certain drugs:
Studies show that urinalysis has over 85% sensitivity for urinary tract infections, and combining it with microscopy improves diagnostic accuracy. In diabetic patients, microalbuminuria is a reliable predictor of renal disease progression.
Clinical guidelines recommend biannual urinalysis for patients with chronic kidney disease, reducing the risk of progression to end-stage renal failure by 30%. Results are also used to evaluate treatment efficacy, such as changes in proteinuria after ACE inhibitor therapy in hypertensive patients.
If urinalysis is positive, further confirmation may include:
However, these alternative tests may require longer waiting times or impose additional burdens on patients. Due to its speed, urinalysis remains the primary screening method.
Usually, no special preparations are required, but it is recommended to avoid vigorous exercise, heavy alcohol consumption, or medications that may affect urine composition (such as certain antibiotics or vitamin C) within 24 hours before testing. Women should avoid urine collection during menstruation to prevent blood interference.
Does abnormal urine test results necessarily indicate a serious disease?Abnormal results do not always mean a severe illness; they should be interpreted in conjunction with clinical symptoms and other tests. For example, occasional proteinuria may be caused by positional changes or exercise, but persistent abnormalities warrant further investigation. The doctor will assess the severity based on individual health status.
Should diet or activities be adjusted after a urine test?Urinalysis itself does not affect daily life, but if potential issues are found (such as diabetes or kidney disease), dietary control (e.g., low salt, low protein diet) or avoiding excessive exertion may be necessary. Specific adjustments should follow medical advice.
What factors influence the accuracy of urine tests?The accuracy may be affected by collection methods, storage time, and the sensitivity of chemical test strips. Urine should be tested within 1 hour of collection; delays can lead to bacterial growth or component breakdown. Using a clean container and avoiding contamination with blood or secretions can improve reliability.
Why are repeated urine tests sometimes necessary?Repeated testing is used to monitor disease progression or treatment effects, such as tracking changes in proteinuria in hypertensive patients or confirming the decline in white blood cell count after infection treatment. Regular follow-up can detect early abnormal trends and adjust treatment strategies accordingly.
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