What does a BUN of 23 indicate in a 15-year-old?

Elevated BUN of 23 in a 15-Year-Old

A BUN of 23 mg/dL in a 15-year-old is mildly elevated above the normal range (7-20 mg/dL) and requires evaluation for potential causes of increased nitrogen waste products, with dehydration being the most common cause in adolescents.

Normal Values and Interpretation

• Normal BUN levels typically range from 7-20 mg/dL (2.5-7.1 mmol/L) 1
• A value of 23 mg/dL represents a mild elevation
• The BUN:creatinine ratio is important for interpretation - a ratio >20:1 suggests pre-renal causes 2

Common Causes of Elevated BUN in Adolescents

Most Likely Causes

1. Dehydration/Volume Depletion

   • Most common cause in adolescents
   • Often due to inadequate fluid intake, excessive exercise, or illness
   • Results in decreased renal perfusion and increased urea reabsorption

2. High Protein Intake

   • Protein supplements or high-protein diets common in adolescent athletes
   • Can cause transient BUN elevation 3
   • Particularly relevant in athletic adolescents

3. Gastrointestinal Bleeding

   • Blood in GI tract serves as protein source leading to increased BUN 2
   • Less common in adolescents but should be considered

Less Common but Important Causes

1. Early Renal Dysfunction

   • Check creatinine to assess for kidney disease
   • Evaluate BUN:creatinine ratio (normal 10-15:1)

2. Catabolic States

   • Significant illness, trauma, or burns
   • Increased protein breakdown leads to higher BUN 2

3. Medications

   • Corticosteroids can increase protein catabolism
   • NSAIDs may affect renal function 1

Evaluation Algorithm

1. Assess Hydration Status

   • Physical examination: skin turgor, mucous membranes, vital signs
   • History of fluid intake, exercise, vomiting, diarrhea

2. Obtain Additional Laboratory Tests

   • Serum creatinine to calculate BUN:creatinine ratio
   • Electrolytes, particularly sodium
   • Urinalysis to assess specific gravity (concentrated in dehydration)

3. Review Dietary History

   • Recent protein intake (supplements, high-protein diets)
   • Changes in eating patterns

4. Medication Review

   • NSAIDs, corticosteroids, other nephrotoxic medications

Management Based on Likely Cause

For Dehydration

• Oral rehydration if mild to moderate
• IV fluids if severe or unable to tolerate oral intake
• Repeat BUN measurement after rehydration

For Diet-Related Elevation

• Modify protein intake if excessive
• Ensure adequate hydration with high-protein diets
• Repeat BUN in 1-2 weeks after dietary modification

For Potential Renal Issues

• Nephrology referral if:
  • BUN remains elevated after addressing hydration
  • Abnormal creatinine or urinalysis
  • Signs of progressive renal dysfunction 1

When to Worry

• BUN >30 mg/dL
• Rising trend on serial measurements
• Accompanying elevated creatinine
• Signs of significant illness or metabolic derangement
• BUN:creatinine ratio >20:1 with clinical signs of illness 2

Follow-up Recommendations

• Repeat BUN and creatinine in 1-2 weeks if mild elevation with identified cause
• Earlier repeat testing if symptoms worsen
• Consider comprehensive metabolic panel if elevation persists

Remember that a single mildly elevated BUN value should be interpreted in clinical context, and in most adolescents represents dehydration that will normalize with adequate fluid intake.