What are the parts of a urinalysis?

Components of a Urinalysis

A complete urinalysis consists of three distinct components: physical examination, chemical analysis (dipstick), and microscopic examination of the urinary sediment. 1, 2

Physical Examination

The physical assessment evaluates the following characteristics:

• Color and clarity of the urine specimen, which can indicate concentration, presence of blood, bilirubin, or other substances 3, 4
• Volume of the specimen collected 3
• Specific gravity, which assesses hydration status and the kidney's concentrating ability 2, 5
• Odor, though this is less clinically significant and may simply reflect concentration rather than infection 2

Chemical Analysis (Dipstick Testing)

The dipstick provides rapid biochemical screening for multiple parameters:

• Leukocyte esterase - detects white blood cells as a surrogate marker for pyuria, with 83% sensitivity and 78% specificity for UTI 1
• Nitrite - indicates bacterial conversion of dietary nitrates (primarily by gram-negative bacteria), with 53% sensitivity but 98% specificity 1
• pH - reflects diet, metabolism, or presence of urinary stones 5
• Protein - screens for proteinuria requiring further quantitative testing 2, 5
• Blood - detects hematuria (both hemoglobin and myoglobin) 2, 5
• Glucose - typically indicates uncontrolled diabetes mellitus 4, 5
• Ketones - suggests illness, starvation, or diabetic ketoacidosis 4, 5
• Bilirubin and urobilinogen - may indicate hepatobiliary disease or hemolysis 4, 5

Microscopic Examination

Microscopic evaluation of the urinary sediment identifies cellular and formed elements:

• White blood cells (WBCs) - pyuria detection with 73% sensitivity and 81% specificity for UTI 1
• Red blood cells (RBCs) - confirms hematuria and can differentiate glomerular from non-glomerular bleeding 1, 3
• Bacteria - direct visualization with 81% sensitivity and 83% specificity for UTI 1
• Epithelial cells - helps assess specimen contamination 3, 4
• Casts (RBC casts, WBC casts, granular casts) - indicate renal parenchymal disease origin 1, 3
• Crystals - may suggest stone disease or metabolic abnormalities 3, 4
• Organisms - identifies yeast, parasites, or other microorganisms 3, 4

Critical Timing and Handling Considerations

The specimen must be fresh - examined within 1 hour at room temperature or within 4 hours if refrigerated - to ensure accuracy of urinalysis results. 1 Changes to urine composition begin immediately after voiding, making proper collection, storage, and handling essential for maintaining specimen integrity 4.

Clinical Integration

For UTI diagnosis specifically, urinalysis cannot substitute for urine culture but must be used in conjunction with it. 1 The American Academy of Pediatrics requires both urinalysis results suggesting infection (pyuria and/or bacteriuria) AND positive culture with ≥50,000 CFU/mL to establish UTI diagnosis 1. The combination of leukocyte esterase AND nitrite OR microscopy positive achieves the highest sensitivity of 99.8% 1, 6.

Common Pitfalls

• Do not skip microscopic examination - 30% of urines with negative macroscopic findings have significant microscopic abnormalities, and 15% of all urines reveal clinically important findings only on microscopy 7
• Cloudy urine may result from precipitated phosphate crystals in alkaline urine rather than infection 2
• Nitrite has limited sensitivity (53%) particularly in infants who void frequently, so negative results do not rule out UTI 1
• Pyuria is absent in approximately 20% of febrile infants with culture-proven pyelonephritis 1, 6