What are the normal reference ranges for routine urine dip‑stick and microscopic analysis in an adult, and what are the Department of Transportation (DOT) requirements for creatinine concentration and specimen temperature for drug‑testing urine samples?

Normal Reference Ranges for Routine Urinalysis in Adults

For routine urine dipstick and microscopic analysis in adults, normal values are: protein <30 mg/g creatinine (or negative/trace on dipstick), albumin <30 mg/g creatinine, red blood cells <3 per high-power field, white blood cells <5 per high-power field, and glucose negative. 1, 2 For Department of Transportation drug testing, urine creatinine must be ≥20 mg/dL and specimen temperature must be 90–100°F (32–38°C) within 4 minutes of collection. 3

Urine Dipstick Reference Ranges

Protein

• Negative or trace is considered normal on dipstick testing 4
• A dipstick reading of ≥1+ warrants quantitative confirmation with spot urine protein-to-creatinine ratio (UPCR) or albumin-to-creatinine ratio (ACR) 5, 4
• Dipstick measures protein concentration (mg/dL), not total excretion, making results highly dependent on urine concentration and unsuitable for accurate quantification 5
• A negative dipstick result (<trace) has a 97.6% negative predictive value for clinically significant proteinuria (ACR ≥30 mg/g) 4

Glucose

• Negative is normal 6
• Glycosuria prevalence in healthy adults is approximately 0.6% 6

Blood/Hematuria

• Negative is normal on dipstick 1
• Any positive heme result on dipstick requires microscopic confirmation of red blood cells before initiating evaluation 1

Nitrite and Leukocyte Esterase

• Negative is normal 7
• Visual and automated dipstick interpretation show almost perfect agreement (κ = 0.82–0.86) for these parameters 7

Microscopic Urinalysis Reference Ranges

Red Blood Cells (RBCs)

• <3 RBCs per high-power field (HPF) is considered normal 1
• ≥3 RBCs/HPF constitutes microscopic hematuria and warrants evaluation, particularly in patients with risk factors for malignancy 1
• Gross (visible) hematuria has a substantially stronger association with cancer and serious underlying conditions compared to microscopic hematuria 1

White Blood Cells (WBCs)

• <5 WBCs/HPF is generally considered normal
• Elevated WBCs suggest urinary tract infection or inflammation 7

Casts and Dysmorphic RBCs

• Absence of red cell casts, white cell casts, or dysmorphic red blood cells is normal 5
• Presence of these elements strongly suggests glomerular disease and warrants nephrology evaluation 5

Quantitative Protein/Albumin Reference Ranges

Spot Urine Protein-to-Creatinine Ratio (UPCR)

• Normal: <200 mg/g (0.2 mg/mg) 1, 5
• Abnormal: ≥200 mg/g indicates pathological proteinuria 1, 5
• In pregnancy, the threshold is higher: ≥300 mg/g (0.3 mg/mg) defines abnormal proteinuria 5

Spot Urine Albumin-to-Creatinine Ratio (ACR)

• Normal (A1): ≤30 mg/g creatinine 1, 2
• Moderately increased albuminuria (A2): 30–299 mg/g (formerly "microalbuminuria") 1, 2
• Severely increased albuminuria (A3): ≥300 mg/g (formerly "macroalbuminuria") 1, 2

24-Hour Urine Protein

• Normal: <150 mg/24 hours (some sources use <300 mg/24 hours as upper limit) 5
• Moderate proteinuria: 300–1000 mg/24 hours 5
• Nephrotic-range proteinuria: >3500 mg/24 hours (>3.5 g/day) 5

Department of Transportation (DOT) Drug Testing Requirements

Urine Creatinine Concentration

• Minimum acceptable: ≥20 mg/dL 3
• Samples with creatinine <20 mg/dL are typically rejected as dilute and unsuitable for drug testing 3
• Creatine supplementation can artificially elevate urine creatinine and mask dilution; mean creatinine concentration increased from 11.6 mg/dL (water only) to 22.5 mg/dL (with 20g creatine) in one study 3

Specimen Temperature

• Acceptable range: 90–100°F (32–38°C) within 4 minutes of collection 3
• Temperature outside this range suggests specimen substitution or adulteration

Important Collection and Interpretation Considerations

Optimal Specimen Timing

• First-morning void is preferred for children and adolescents to avoid orthostatic (postural) proteinuria 1, 5, 2
• Random daytime specimens are acceptable for adults 2

Pre-Collection Instructions

• Avoid vigorous exercise for 24 hours before collection, as physical activity causes transient proteinuria elevation 1, 5
• Avoid collection during menstruation, as blood contamination produces false-positive results 5
• Treat urinary tract infections first and retest after resolution, as symptomatic UTIs cause transient proteinuria 5

Confirmation Requirements

• Persistent proteinuria is defined as 2 of 3 positive samples over 3 months 1, 5
• Single elevated values should not be considered diagnostic without confirmation 2

Sample Stability

• Urine creatinine is virtually unaffected by storage time and temperature except under extreme conditions (30 days at 55°C) 8
• Storage for 2 days at 55°C causes <3% decrease in creatinine levels 8
• Refrigeration at 4°C is recommended for samples assayed the same or next day 1

Common Pitfalls to Avoid

• Do not rely on dipstick alone for quantitative assessment; always confirm with UPCR or ACR 5, 4
• Do not interpret isolated urine creatinine elevation as pathological; only the protein-to-creatinine or albumin-to-creatinine ratio matters 9
• Do not order 24-hour collections routinely; spot UPCR/ACR is sufficient for most clinical scenarios 1, 5
• Do not assume serum creatinine of 1.2 mg/dL is "normal" without calculating eGFR, especially in elderly, women, or those with low muscle mass 5
• Be aware that automated and visual dipstick analysis show only moderate agreement for erythrocytes (κ = 0.51) but almost perfect agreement for nitrite and leukocyte esterase 7