Guidelines for Urinalysis
Urinalysis should include comprehensive physical, chemical, and microscopic examinations, with the specimen examined within two hours of collection to ensure accuracy. 1
Specimen Collection and Timing
Midstream clean-catch collection is acceptable in most clinical situations, though catheterization may be required when clean-catch specimens cannot be reliably obtained (e.g., vaginal contamination, obesity, phimosis in uncircumcised men). 2
The specimen must be fresh—examined within 1 hour at room temperature or within 4 hours if refrigerated—to maintain sensitivity and specificity of urinalysis findings. 2
For women, urethral and vaginal examinations should be performed to exclude local causes of microscopic hematuria, and catheterized specimens may be needed if vaginal contamination is suspected. 2
Components of Complete Urinalysis
Physical Examination
Assess color, clarity, and volume, recognizing that cloudy urine often results from precipitated phosphate crystals in alkaline urine rather than infection, and strong odor may reflect concentrated urine rather than UTI. 1
Specific gravity provides reliable assessment of hydration status and should be routinely evaluated. 1
Chemical Analysis (Dipstick)
Dipstick urinalysis is convenient but prone to false-positive and false-negative results, requiring correlation with clinical context and microscopic findings. 1
Test for leukocyte esterase, nitrites, protein, blood, glucose, ketones, bilirubin, urobilinogen, and pH. 1, 3
The leukocyte esterase test has 83% sensitivity and 78% specificity for UTI, while the nitrite test has only 53% sensitivity but 98% specificity. 2
Nitrite testing is particularly insensitive in children and infants who empty their bladders frequently (requiring ~4 hours for bacterial conversion of nitrates), and not all uropathogens reduce nitrate to nitrite. 2
Microscopic Examination
Microscopic examination of urinary sediment is essential and must not be omitted, as 30% of urines with negative macroscopic exams show significant microscopic findings. 4
Evaluate for red blood cells, white blood cells, bacteria, epithelial cells, crystals, and casts. 1, 3
Determine the number of RBCs per high-power field and note the presence of dysmorphic RBCs or RBC casts, which suggest glomerular bleeding. 2
Heavy proteinuria with RBCs and RBC casts strongly suggests acute glomerulonephritis, while mild proteinuria without microscopic findings suggests nephrosclerosis, interstitial nephritis, or acute tubular necrosis. 5
Clinical Context for Ordering Urinalysis
When Urinalysis IS Indicated
Screen for asymptomatic bacteriuria in adults ≥60 years, diabetic patients of any age, pregnant women, and adolescents. 6
Obtain urinalysis and urine culture prior to treatment in patients with suspected acute pyelonephritis, symptoms not resolving or recurring within 4 weeks after treatment, atypical symptoms, pregnant women, and recurrent UTIs. 7
In older adults, urinalysis helps differentiate UTI from other causes of genitourinary symptoms. 7
In pediatric patients, urinalysis is essential as young children cannot verbalize symptoms to distinguish cystitis from pyelonephritis. 7
For suspected UTI in febrile infants and children 2-24 months, urinalysis suggesting infection (pyuria and/or bacteriuria) plus ≥50,000 CFU/mL of uropathogen from catheterized or suprapubic aspiration specimen establishes diagnosis. 2
When Urinalysis May NOT Be Needed
In women with uncomplicated UTI presenting with classic symptoms of dysuria, frequency, and urgency, empiric treatment without urinalysis is acceptable, as dysuria alone has high diagnostic accuracy. 7
In simple uncomplicated cystitis in healthy nonpregnant patients, routine cultures are not necessary. 2
Critical Caveat About Diagnostic Limitations
While absence of pyuria can help rule out infection in most populations, the positive predictive value of pyuria for diagnosing UTI is exceedingly low, as pyuria often indicates genitourinary inflammation from many noninfectious causes. 2
Evidence-based UTI diagnosis should be primarily based on clinical symptoms, with UA findings integrated but not relied upon solely. 2
Evaluation of Specific Findings
Hematuria
Evaluation of hematuria always requires both dipstick analysis and microscopic examination. 6
For asymptomatic microscopic hematuria in adults, complete urologic evaluation includes history, physical examination, laboratory analysis, radiologic imaging of the upper urinary tract, and cystoscopic examination of the bladder. 2
If careful history suggests benign causes (menstruation, vigorous exercise, sexual activity, trauma), repeat urinalysis 48 hours after cessation of the activity—no additional evaluation is warranted if hematuria resolves. 2
Patients with microscopic hematuria and urinary tract infection should be treated appropriately, with urinalysis repeated six weeks after treatment; if hematuria resolves, no additional evaluation is necessary. 2
Proteinuria
Positive protein on dipstick should be evaluated in conjunction with other clinical and laboratory data (patient's age, physical findings, renal function, microscopic urinalysis results). 6
Transient proteinuria is typically benign, but persistent proteinuria requires further work-up. 1
Bacteriuria
Uncomplicated UTIs diagnosed by positive leukocyte esterase and nitrite tests can be treated without culture. 1
Do not screen or treat asymptomatic bacteriuria except in pregnant women and before urological procedures breaching the mucosa. 2, 7
Common Pitfalls to Avoid
Never obtain urinalysis or urine culture after antibiotics have been started if definitive diagnosis is needed, as antimicrobial therapy sterilizes urine rapidly, leading to false-negative results. 7
Do not rely on urinalysis/culture obtained after antibiotics to rule out UTI—negative results likely reflect antibiotic effect rather than absence of infection. 7
Do not use urine collection bag specimens to document UTI—"positive" cultures from bag specimens require confirmation with catheterized or suprapubic aspiration specimens. 2
Avoid routine UA and urine cultures for fever workup in hospitalized patients, as this leads to unnecessary testing and antimicrobial use, particularly since UTIs are infrequently the fever source without urinary tract obstruction. 2