What tests are included in a urinalysis?

Urinalysis Components and Testing

A complete urinalysis consists of three essential components: physical examination (color, clarity, odor, volume, specific gravity), chemical analysis via dipstick testing (pH, protein, glucose, ketones, blood, bilirubin, urobilinogen, nitrite, leukocyte esterase), and microscopic examination of urine sediment (red blood cells, white blood cells, bacteria, epithelial cells, crystals, casts). 1, 2

Physical Examination Parameters

The physical assessment evaluates several key characteristics:

• Color and clarity: Normal urine is pale to dark yellow and clear; cloudy urine often results from precipitated phosphate crystals in alkaline urine or may indicate pyuria 2
• Odor: Strong odors may reflect concentrated specimens rather than infection 2
• Volume: Assessed when relevant to clinical context 3, 1
• Specific gravity: Provides reliable assessment of hydration status, with normal values typically ranging from 1.003 to 1.030 2

Chemical Dipstick Testing

The dipstick provides rapid semiquantitative results for multiple parameters:

• pH: Measures urine acidity/alkalinity (normal range 4.5-8.0) 3, 1
• Protein: Detects albuminuria; positive results require correlation with clinical context and microscopic findings 4, 2
• Glucose: Present when blood glucose exceeds renal threshold (typically >180 mg/dL), though plasma glucose measurement is preferred for diabetes screening 4
• Ketones: Indicates fat metabolism, seen in diabetic ketoacidosis, starvation, or low-carbohydrate diets 3, 1
• Blood/hemoglobin: Detects hematuria, hemoglobinuria, or myoglobinuria through peroxidase activity 3, 2
• Bilirubin: Elevated in hepatobiliary disease or hemolysis 3, 1
• Urobilinogen: Reflects hemoglobin breakdown; levels vary with liver function and hemolysis 3, 1
• Nitrite: Indicates presence of nitrate-reducing bacteria (primarily gram-negative organisms); requires 4-hour bladder dwell time for conversion 5, 6
• Leukocyte esterase: Detects pyuria with 83% sensitivity and 78% specificity; combined with nitrite testing achieves 93% sensitivity for UTI 6, 7

Critical Dipstick Limitations

Dipstick testing is convenient but prone to errors. False-positive results occur with contaminated specimens, oxidizing agents, and certain medications including phenazopyridine 7, 2. False-negative results may occur with high urinary glucose, elevated specific gravity, or antibiotic presence 6. Dipstick results should never be used alone for clinical decision-making and require microscopic confirmation, particularly for hematuria (≥3 RBCs/HPF threshold) and pyuria (≥10 WBCs/HPF threshold). 6, 7

Microscopic Examination

Microscopic sediment analysis is essential for patients with renal or urinary tract disease:

• Red blood cells: ≥3 RBCs per high-power field defines microscopic hematuria; requires evaluation for glomerular, renal, or urologic causes 7, 2
• White blood cells: ≥10 WBCs/HPF indicates pyuria; combined with symptoms suggests UTI, but alone has low positive predictive value due to high asymptomatic bacteriuria prevalence (15-50% in elderly) 6
• Bacteria: Presence on Gram stain of fresh uncentrifuged urine correlates with ≥10⁵ CFU/mL 6
• Epithelial cells: High counts indicate contamination and necessitate repeat collection 6
• Crystals: Type varies with urine pH and may indicate metabolic disorders or medication effects 3, 1
• Casts: Cylindrical structures formed in renal tubules; types include hyaline, granular, cellular (RBC, WBC), and pathologic casts indicating specific renal pathology 3, 1

Specimen Collection and Handling

Proper collection and timely processing are critical for accurate results. Midstream clean-catch collection is acceptable for most situations, though catheterization or suprapubic aspiration is preferred in infants, young children, and women unable to provide clean specimens 6, 7.

Time-Sensitive Processing Requirements

Specimens must be processed within 1 hour at room temperature or refrigerated (4-10°C) within 1 hour for processing up to 24 hours later. 6, 8 Delays beyond 2 hours at room temperature cause bacterial overgrowth in 32% of specimens, producing false-positive results and diagnostic errors with an odds ratio of 73.89 for shifting between significant and non-significant growth 8. Refrigeration maintains diagnostic accuracy with 87.3-82.6% agreement for high bacterial counts (≥10⁵ CFU/mL) but shows lower agreement (55.2-45.8%) for moderate counts (10⁴-10⁵ CFU/mL) 8.

Clinical Context for Ordering

Urinalysis should be ordered selectively rather than routinely. Screening is recommended for adults ≥60 years, diabetic patients, pregnant women, and adolescents to detect asymptomatic bacteriuria. 4 For symptomatic patients with dysuria, frequency, urgency, fever, or gross hematuria, urinalysis aids UTI diagnosis when combined with clinical assessment 6. Hematuria evaluation always requires both dipstick analysis and microscopic examination, with confirmation in two of three properly collected specimens for microscopic hematuria, though high-risk patients warrant full urologic evaluation after a single properly performed urinalysis documenting ≥3 RBCs/HPF. 7

Common Pitfalls

Never rely solely on dipstick results without microscopic confirmation, particularly for hematuria where dipstick specificity is only 65-99% 7. Avoid attributing hematuria to antiplatelet or anticoagulant therapy without investigation, as gross hematuria carries a 7.2 odds ratio for urologic cancer 7. Do not order urinalysis or culture in asymptomatic patients, as asymptomatic bacteriuria (present in 15-50% of elderly long-term care residents) should not be treated except in pregnant women or patients undergoing urologic procedures with anticipated mucosal bleeding 6. The combination of negative leukocyte esterase and negative nitrite effectively rules out UTI with 90.5% negative predictive value, making bacterial UTI extremely unlikely regardless of symptoms. 6