Urinalysis is one of the oldest and most frequently ordered laboratory tests. A complete urinalysis has three components: physical examination, chemical dipstick analysis, and microscopic sediment examination.

Specimen Collection

A midstream clean-catch urine specimen is preferred. The patient cleans the urethral area, begins voiding, collects the middle portion in a sterile container, and finishes voiding. This minimizes contamination from the urethra and skin.

The first morning void is most concentrated and provides the best sensitivity. If not tested within 1 hour, the specimen should be refrigerated at 2–8 °C. Allow refrigerated samples to return to room temperature before testing.

Physical Examination

• Color: normal urine is pale yellow to amber (urochrome pigment). Abnormal colors include red (blood, beets), dark brown (bilirubin, myoglobin), orange (rifampin, dehydration), green (biliverdin, certain drugs), and turbid (infection, phosphate crystals).
• Clarity: clear, slightly hazy, or turbid. Turbidity indicates cells, bacteria, crystals, or lipid.
• Specific gravity: measured by refractometer or dipstick. Normal range is 1.005–1.030. High specific gravity indicates concentrated urine (dehydration, SIADH); low indicates dilute urine (diabetes insipidus, excessive fluid intake).
• pH: normally 4.5–8.0. Diet, drugs, and metabolic state affect pH. Alkaline urine can indicate a urinary tract infection with urea-splitting organisms (Proteus).

Dipstick Chemistry

The reagent strip (dipstick) has pads impregnated with chemicals that react with specific analytes. Results are read semiquantitatively (negative, trace, 1+, 2+, 3+) at a defined time (usually 60–120 seconds).

• Glucose: normally absent. Present in hyperglycemia (diabetes) or renal glycosuria.
• Protein: trace amounts may be normal. Persistent proteinuria indicates kidney damage (glomerulonephritis, nephrotic syndrome).
• Blood: detects hemoglobin and myoglobin. Hematuria (intact RBCs) indicates bleeding; hemoglobinuria indicates intravascular hemolysis.
• Ketones: acetoacetate and acetone. Present in diabetic ketoacidosis, starvation, and ketogenic diets.
• Nitrite: produced by nitrate-reducing bacteria (most Enterobacteriaceae). A positive test suggests bacteriuria.
• Leukocyte esterase: an enzyme released by white blood cells. Positive indicates pyuria (UTI or inflammation).
• Bilirubin and urobilinogen: indicate liver function and hemolysis.

Microscopic Examination

The sediment is examined after centrifuging 10 mL of urine at 1500–2000 rpm for 5 minutes and resuspending the pellet in 0.5–1 mL of supernatant. A drop is placed on a slide, coverslipped, and examined under high power (400×).

• Red blood cells: >3 per HPF is abnormal (hematuria). Dysmorphic RBCs suggest glomerular origin.
• White blood cells: >5 per HPF suggests inflammation or infection (pyuria).
• Epithelial cells: squamous cells indicate contamination; renal tubular cells may indicate tubular injury.
• Casts: cylindrical structures formed in renal tubules. Hyaline casts can be normal; RBC casts indicate glomerulonephritis; WBC casts indicate pyelonephritis; granular and waxy casts indicate renal tubular injury.
• Crystals: calcium oxalate (common, usually benign), uric acid, triple phosphate (struvite), cystine (cystinuria).
• Bacteria and yeast: bacteria are common in contaminated specimens; significant bacteriuria (>10⁵ CFU/mL) indicates infection.