Urinalysis

Classic UTI findings: positive leukocyte esterase (LE), positive nitrite, pyuria (WBC >5/HPF), bacteriuria. Key points: Nitrite is specific but not sensitive — only gram-negative organisms that convert nitrate to nitrite (E. coli, Klebsiella) turn it positive. Enterococcus, Pseudomonas, and Staph saprophyticus are nitrite-negative. Asymptomatic bacteriuria should NOT be treated except in pregnancy and before urologic procedures. LE can be falsely positive with vaginal contamination.

Dipstick detects albumin only (misses Bence Jones proteins/light chains). Trace or 1+ may be benign (fever, exercise, dehydration). Persistent 1+ or greater requires quantification with spot urine albumin-to-creatinine ratio (UACR) or protein-to-creatinine ratio. UACR 30-300 mg/g = moderately increased albuminuria (formerly microalbuminuria). UACR >300 mg/g = severely increased. Always confirm with repeat testing. Common causes: diabetic nephropathy, hypertensive nephrosclerosis, glomerulonephritis.

Microscopic hematuria (>3 RBC/HPF) requires evaluation. Glomerular origin: dysmorphic RBCs, RBC casts, concurrent proteinuria — suggests glomerulonephritis, IgA nephropathy. Non-glomerular: isomorphic RBCs, no casts — consider UTI, nephrolithiasis, malignancy (bladder, renal, prostate). AUA guidelines for microhematuria evaluation: age >35 or risk factors (smoking, chemical exposure) → CT urogram + cystoscopy. Always rule out benign causes first: menstruation, recent exercise, UTI, instrumentation.