Urinalysis

Urinalysis is the physical, chemical, and microscopic examination of urine. Because urine is easy to collect and reflects both kidney function and systemic metabolism, urinalysis is one of the most commonly ordered laboratory tests, used for routine screening, diagnosing urinary complaints, and monitoring known disease.

The test has three components. The physical examination assesses color, clarity, and specific gravity (a measure of concentration). The chemical examination, usually performed with a reagent dipstick, screens for glucose, ketones, protein, blood, bilirubin, urobilinogen, nitrites, leukocyte esterase, and pH. The microscopic examination of centrifuged sediment identifies red and white blood cells, bacteria, epithelial cells, crystals, and casts — cylindrical structures formed in the renal tubules whose type can localize disease to the kidney itself.

Patterns of findings point toward diagnoses. Nitrites plus leukocyte esterase with bacteria suggest a urinary tract infection; glucose and ketones raise concern for uncontrolled diabetes; protein suggests glomerular disease; red cell casts indicate glomerulonephritis, as in post-streptococcal glomerulonephritis, while white cell casts suggest pyelonephritis or interstitial nephritis. Proper collection matters — a clean-catch midstream specimen limits contamination, and prompt testing prevents degradation.

Urinalysis is tested from two angles on healthcare exams. The CCMA exam covers specimen collection, dipstick and physical testing, and CLIA-waived procedures a medical assistant performs, while USMLE Step 1 emphasizes interpreting sediment findings — especially casts — to localize renal pathology.