NCLEX Review Guide: Urinary Renal Diagnostic Tests

Blood Urea Nitrogen (BUN)

• Normal range: 10-20 mg/dL - measures urea nitrogen, a waste product filtered by kidneys
• Elevated BUN indicates kidney dysfunction, dehydration, or high protein intake
• Critical value >100 mg/dL may indicate uremia requiring immediate intervention

Serum Creatinine

• Normal: Males 0.6-1.2 mg/dL, Females 0.5-1.1 mg/dL - most reliable indicator of kidney function
• Creatinine is produced by muscle metabolism and exclusively filtered by kidneys
• Doubling of creatinine indicates 50% loss of kidney function

Physical Characteristics

• Specific gravity: 1.003-1.030 measures urine concentration ability
• High specific gravity (>1.030) indicates dehydration or diabetes mellitus
• Low specific gravity (<1.010) suggests diabetes insipidus or overhydration

Chemical Analysis

• Protein: <0.8 mg/dL normal - proteinuria indicates glomerular damage
• Glucose: Negative normal - glycosuria appears when blood glucose >180 mg/dL
• Ketones present indicate diabetic ketoacidosis or starvation

Creatinine Clearance

• Normal: 85-135 mL/min - measures glomerular filtration rate (GFR)
• Requires 24-hour urine collection with precise timing
• Patient must void completely at start time and save all subsequent urine

1. Have patient void and discard at start time (8 AM)
2. Collect ALL urine for next 24 hours
3. End collection with final void at exactly 8 AM next day
4. Keep specimen refrigerated throughout collection

Imaging Studies

• IVP (Intravenous Pyelogram) uses contrast dye to visualize urinary tract structure
• Check for iodine/shellfish allergy before contrast procedures
• Ultrasound is non-invasive first-line imaging for kidney assessment