A urinalysis (UA) is a common, non-invasive diagnostic procedure used to assess a person’s overall health and metabolic status. The test involves collecting and analyzing a urine sample to detect and measure various compounds the body eliminates. Urine analysis reflects the function of the kidneys and urinary tract, providing clues about systemic diseases like diabetes or liver issues. It is a primary tool for healthcare providers for initial screening and managing a wide range of disorders.
The Three Components of a Urinalysis
A complete urinalysis consists of three distinct examinations: physical, chemical, and microscopic. The physical examination, or macroscopic assessment, is the initial step involving visual inspection of the urine sample. Technicians observe the color (pale yellow to amber) and clarity (clear, hazy, cloudy, or turbid). They also measure the specific gravity, which gauges the kidney’s ability to concentrate or dilute urine, reflecting the patient’s hydration status.
The chemical examination uses a reagent strip, commonly called a dipstick, embedded with chemicals that change color when exposed to specific substances. This rapid test measures several chemical parameters simultaneously, including the urine’s acidity (pH), which typically ranges from 4.5 to 8.0. The dipstick screens for protein, glucose, ketones, bilirubin, and blood, which are normally absent or present only in trace amounts. It also measures leukocyte esterase (an enzyme from white blood cells) and nitrites (a byproduct of certain bacteria), which strongly indicate a possible infection.
The final component is the microscopic examination, where a concentrated drop of urine sediment is viewed under a high-powered microscope. This step identifies and quantifies various solid elements suspended in the urine. Technicians look for red blood cells, white blood cells, epithelial cells shed from the urinary tract, and microorganisms like bacteria and yeast. They also identify urinary casts (cylindrical structures formed in the kidney tubules) and crystals, which are precipitates that can signal potential kidney stone formation.
Why Doctors Order This Test
Healthcare providers routinely order a urinalysis for screening, diagnosis, and monitoring purposes. As a screening tool, the UA is often included in routine annual physical examinations or pre-surgical workups to detect conditions before symptoms appear. It is also used during prenatal care to screen for issues like gestational diabetes or preeclampsia.
For diagnosis, the test is requested when a patient presents with specific symptoms, such as painful or frequent urination, abdominal or back pain, or visible blood in the urine. Analyzing the sample helps quickly identify the cause of these symptoms, such as a urinary tract infection (UTI) or kidney stones. For example, detecting nitrites and leukocyte esterase strongly suggests a bacterial infection within the urinary tract.
The urinalysis is also used for monitoring the progression of chronic conditions and the effectiveness of treatment plans. Patients with long-term diseases like diabetes, hypertension, or known kidney disease may have the test performed regularly. Monitoring levels of protein or glucose helps clinicians track disease management and allows for timely adjustments to medications or lifestyle recommendations.
Interpreting Abnormal Results
Interpreting an abnormal urinalysis connects specific findings from the three examinations to potential underlying health issues. A positive result for glucose or ketones indicates poorly controlled diabetes mellitus. Normally, kidneys reabsorb almost all filtered glucose; its presence in the urine (glycosuria) suggests blood sugar levels have exceeded the kidney’s reabsorption threshold, typically around 180 milligrams per deciliter. Ketones, byproducts of fat metabolism, appear when the body breaks down fat for energy due to a lack of available glucose, often seen in uncontrolled diabetes or prolonged starvation.
The presence of protein (proteinuria) often signals kidney damage or disease. While trace amounts may occur after intense exercise or during a fever, consistently elevated levels indicate compromised glomerular filtration within the kidney. Finding cellular casts, which are microscopic molds of the kidney tubules (like red blood cell casts or waxy casts), points directly to significant kidney pathology, such as glomerulonephritis or chronic kidney failure.
For infection, a positive result for leukocyte esterase or nitrites, combined with a high count of white blood cells (pyuria) and bacteria, strongly suggests a UTI. Nitrites are produced when certain bacteria, such as E. coli, convert urinary nitrate, and leukocyte esterase indicates the body’s immune response. The presence of red blood cells (hematuria) can stem from various causes, ranging from UTIs and kidney stones to more serious conditions like bladder or kidney cancer, requiring further investigation.
Bilirubin, a waste product from the breakdown of old red blood cells, should not be detectable in the urine. Its presence, along with increased urobilinogen, can indicate liver disease (such as hepatitis or cirrhosis) or a blockage of the bile ducts. Abnormal urine color, such as dark yellow or amber, is a visual clue for excessive bilirubin excretion, prompting follow-up testing.
Preparing for and Providing a Sample
The accuracy of a urinalysis relies heavily on collecting a proper, uncontaminated sample, typically using the “clean catch” midstream technique. Before collection, the patient should wash their hands thoroughly with soap and water to minimize external bacterial contamination. The collection kit usually includes sterile wipes for cleansing the genital area, which is crucial for removing surface bacteria that could skew results, especially when diagnosing a UTI.
For cleansing, individuals with female anatomy should wipe the spread labia from front to back. Those with male anatomy should cleanse the tip of the penis, retracting the foreskin if needed. The patient should begin urinating into the toilet for a few seconds to flush out microbes from the urethra. The specimen cup is then placed into the stream to collect the “midstream” portion, filling it about halfway. This midstream technique ensures the sample represents the urine in the bladder, free from external contaminants flushed out by the initial flow.
Certain factors can interfere with results, potentially leading to false positives or negatives. Menstruation can cause blood contamination, so patients should inform their provider if they are on their period. Taking certain medications, such as vitamin C supplements, some antibiotics, or specific pain relievers, can also alter the dipstick’s chemical readings. Additionally, extreme hydration or dehydration significantly affects the specific gravity and concentration of substances, so excessive fluid intake just before the test is discouraged.