Urine Test — Purpose, Procedure & Normal Values | MyMedicPlus

A urine test (urinalysis) is one of the most frequently performed and clinically versatile diagnostic tests in medicine, providing rapid, cost-effective information about renal function, urinary tract integrity, systemic metabolic states, and infectious processes. It analyses the physical, chemical, and microscopic properties of a urine sample to detect a broad range of abnormalities. A standard urinalysis comprises three main components: dipstick testing — a chemically impregnated plastic strip with multiple reagent pads, each changing colour in proportion to the concentration of a specific analyte (glucose, protein, blood, nitrites, leucocyte esterase, pH, specific gravity, ketones, bilirubin, and urobilinogen); microscopic examination — centrifugation of the urine followed by examination of the sediment under a light microscope at 100x and 400x magnification by a laboratory scientist, identifying and counting red blood cells, white blood cells, renal tubular epithelial cells, casts (cylindrical structures formed in the distal tubule — RBC casts, WBC casts, granular casts, waxy casts), crystals (calcium oxalate, uric acid, struvite), and bacteria; and urine culture and sensitivity — inoculation of urine onto selective agar plates and incubation at 37°C for 24–48 hours to identify and quantify bacterial growth, with antibiotic susceptibility (sensitivity) testing performed on any significant growth to guide appropriate treatment selection.

Urine tests are ordered for a wide range of clinical indications. To diagnose urinary tract infections (UTIs): uncomplicated cystitis (lower UTI, most common in women), pyelonephritis (upper UTI with systemic features — fever, loin pain, rigors), urethritis, and prostatitis. To investigate haematuria (blood in the urine): visible (macroscopic or gross haematuria) or microscopic haematuria discovered incidentally or on dipstick screening. To detect and monitor renal (kidney) disease: proteinuria (protein in urine) indicating glomerulonephritis, diabetic nephropathy, hypertensive nephrosclerosis, or nephrotic syndrome; urinary casts indicating specific nephron segment damage. To screen for and monitor diabetes mellitus: glucosuria (glucose spilling into urine when blood glucose exceeds approximately 180 mg/dL) and ketonuria (in diabetic ketoacidosis). To assess hydration status (specific gravity, colour). To evaluate liver disease: bilirubinuria and raised urobilinogen. For preeclampsia monitoring in pregnancy: significant proteinuria is a diagnostic criterion for preeclampsia. As part of workplace drug testing and pre-employment medical screening. As a routine component of annual health checks, insurance medicals, and pre-operative assessment.

Collect a mid-stream clean-catch urine sample using the following technique: clean the urethral meatus (opening) with the antiseptic wipe provided in the specimen kit; begin urinating into the toilet for the first 2–3 seconds to flush away urethral contamination; then, without stopping the flow, collect the midstream (middle portion) of the urine stream into the sterile, wide-mouthed specimen container provided; finish urinating into the toilet. This clean-catch mid-stream technique is critical for reducing contamination of the sample with periurethral bacteria, squamous epithelial cells, and mucus, which can cause false-positive dipstick and culture results. For a urine culture intended to identify a urinary tract infection, the first morning specimen (the most concentrated urine of the day, with the highest bacterial count if infection is present) is ideal. Avoid collecting urine during active menstruation, as blood contamination produces false-positive blood and protein results. Some medications (rifampicin — bright orange, pyridium — vivid orange) and foods (beetroot — pink/red, vitamin B2/riboflavin — fluorescent yellow, blackberries) discolour urine normally without indicating pathology. Label the container with your name and date, and deliver it to the laboratory within 2 hours of collection, or refrigerate at 4°C for up to 24 hours.

The urine sample undergoes a structured analysis in three stages in the laboratory. Visual inspection: the laboratory staff first assess colour (normal pale to amber yellow, concentrated yellow, or pathological colours such as red-brown for haematuria, dark brown for bilirubinuria, cloudy-white for pyuria), clarity (clear, hazy, or turbid), and odour (normal faintly aromatic; offensive ammonia smell suggests infection; sweet fruity odour suggests ketonuria). Dipstick analysis: a reagent strip is dipped into the urine for one second, removed, and read at specified time intervals (1–2 minutes) by comparing the colour of each reagent pad against the printed reference chart on the container, or more commonly by automated dipstick reader for objective, reproducible measurements. Microscopy: a measured aliquot of urine (typically 10 mL) is centrifuged at 400g for 5 minutes, the supernatant is decanted leaving approximately 0.5 mL, and the resuspended sediment is placed on a glass slide with a coverslip and examined systematically at low (100x) and high (400x) magnification. Results are reported as counts per high-power field (HPF). Culture: the urine is inoculated with a calibrated bacteriological loop onto chromogenic agar or blood agar plates, incubated at 37°C for 24–48 hours, and colonies are identified by morphology and biochemical testing; antibiotic sensitivity is determined by the disc diffusion (Kirby-Bauer) or minimum inhibitory concentration (MIC) method.

Normal urinalysis reference values: Colour — pale yellow to amber; Clarity — clear; pH — 4.5–8.0 (typically 5.5–6.5 with a normal diet); Specific gravity — 1.005–1.030 (low in overhydration/diabetes insipidus; high in dehydration); Protein — negative (less than 150 mg/24 hours or less than 30 mg/g albumin-to-creatinine ratio); Glucose — negative (blood glucose must exceed approximately 180 mg/dL for glucosuria to appear); Blood — negative (up to 2–3 RBC/HPF may be acceptable); Leucocytes (leucocyte esterase) — negative; Nitrites — negative; Ketones — negative; Bilirubin — negative; Urobilinogen — normal trace. Interpretation of abnormal dipstick results: Protein positive — suggests renal disease (confirm with albumin-to-creatinine ratio or 24-hour urine protein collection); Glucose positive — hyperglycaemia (diabetes) or renal glycosuria; Blood and nitrites and leucocytes — consistent with bacterial UTI; Blood alone — kidney stones, bladder pathology, or glomerulonephritis; Nitrites alone — gram-negative bacteria present; Leucocytes alone — pyuria without bacteriuria (sterile pyuria — consider renal tuberculosis, chlamydia, or interstitial nephritis). Microscopy findings: RBC casts — glomerulonephritis (pathognomonic); WBC casts — pyelonephritis or interstitial nephritis; granular and waxy casts — advanced chronic kidney disease. A positive urine culture with 100,000 CFU/mL (10^5 colony-forming units per millilitre) or more of a single uropathogen confirms urinary tract infection; 10,000–100,000 CFU/mL is equivocal and clinically interpreted in context.

Urine collection is a completely non-invasive and safe procedure with no physical risks. The principal limitations of urinalysis relate to specimen quality and test specificity. Sample contamination from improper collection technique (failure to clean the urethral area, collection of the initial rather than midstream urine, or sample collection during menstruation) is the most common cause of false-positive dipstick results for leucocytes, blood, nitrites, and protein, and of false-positive culture results showing polymicrobial growth or low-count growth of multiple organisms — so-called 'mixed growth' or 'contaminated specimen'. The dipstick is a sensitive screening tool but has significant analytical limitations: leucocyte esterase detects white cells but cannot identify the causative organism or distinguish bacterial UTI from sterile pyuria; nitrites are specific for gram-negative bacteria that reduce dietary nitrate but are negative in gram-positive UTI (Enterococcus, Staphylococcus saprophyticus) and in infections caused by Pseudomonas or Candida; protein detection by dipstick is insensitive below 300 mg/L and unreliable with very dilute urine — quantitative albumin-to-creatinine ratio (ACR) from a spot sample or 24-hour urine protein is required to accurately diagnose and quantify proteinuria for renal disease monitoring. Culture results take 24–48 hours, during which empirical antibiotic therapy based on local resistance patterns may be initiated for symptomatic patients and adjusted once sensitivities are available.