What should be investigated in a 25-year-old female with no known co-morbid illnesses and elevated Blood Urea Nitrogen (BUN) levels, who is undergoing pre-employment clearance?

Evaluation of Isolated Elevated BUN in a Young, Healthy Female

In this 25-year-old healthy female with isolated elevated BUN, you should investigate all of the above: GI bleeding, steroid use, and hypercatabolic states, as these are the primary pre-renal and increased production causes of elevated BUN with preserved kidney function.

Understanding the Clinical Scenario

This patient presents with an isolated elevation in BUN without other symptoms or known comorbidities, which suggests either:

• Pre-renal azotemia (decreased renal perfusion without intrinsic kidney damage)
• Increased urea production (hypercatabolic state)
• GI bleeding (protein load from blood digestion)

The normal absence of other symptoms makes intrinsic renal disease less likely, but a systematic evaluation is essential 1.

Specific Elements to Investigate

A. Gastrointestinal Bleeding

Why this matters: Blood in the GI tract acts as a high protein load that is digested and absorbed, significantly increasing BUN production 1, 2.

• Ask specifically about:
  • Melena (black, tarry stools)
  • Hematochezia (bright red blood per rectum)
  • Hematemesis or coffee-ground emesis
  • Recent NSAID use (which can cause gastritis/ulcers)
  • History of peptic ulcer disease or gastritis
  • Easy bruising or bleeding tendencies

B. Steroid Use

Why this matters: Corticosteroids increase protein catabolism and can elevate BUN through increased breakdown of muscle and other proteins 3.

• Inquire about:
  • Current or recent corticosteroid use (oral, inhaled, topical, or injected)
  • Dose and duration of any steroid therapy
  • Use for conditions like asthma, allergies, autoimmune disorders, or dermatologic conditions

C. Hypercatabolic States

Why this matters: Any condition causing increased protein breakdown will elevate BUN production 2, 4.

• Assess for:
  • High protein intake: Dietary history, protein supplements, high-protein diets 4
  • Fever or infection: Recent illness, current symptoms of infection
  • Trauma or surgery: Recent injuries or procedures
  • Starvation or malnutrition: Paradoxically causes protein catabolism from muscle breakdown
  • Hyperthyroidism: Increases metabolic rate and protein turnover
  • Tetracycline use: Anti-anabolic effect increases BUN

Additional Critical Assessments

Volume Status Evaluation

Dehydration is a common cause of isolated BUN elevation in young, healthy individuals 1, 5.

• Check for:
  • Orthostatic vital signs (blood pressure and heart rate changes from lying to standing) 1
  • Mucous membrane moisture 5
  • Skin turgor
  • Recent decreased fluid intake or increased losses (vomiting, diarrhea, excessive sweating, diuretic use)
  • Urine output and concentration

Medication Review

Beyond steroids, evaluate for 1, 5:

• NSAIDs: Decrease renal perfusion and can cause both GI bleeding and pre-renal azotemia
• Diuretics: Can cause volume depletion
• ACE inhibitors/ARBs: Affect renal hemodynamics
• Any nephrotoxic medications

Essential Laboratory Follow-up

Calculate the BUN/Creatinine ratio 1, 5:

• Ratio >20:1 suggests pre-renal azotemia (dehydration, decreased perfusion, GI bleeding, high protein intake)
• Ratio 10-20:1 suggests intrinsic renal disease (less likely in this case)

Obtain additional labs 3, 1:

• Complete metabolic panel (electrolytes, calcium, albumin)
• Complete blood count (to assess for anemia from GI bleeding)
• Urinalysis (to rule out intrinsic kidney disease)
• Estimated GFR calculation

Clinical Pitfalls to Avoid

• Do not assume normal kidney function based on lack of symptoms alone - obtain creatinine and calculate eGFR 1, 2
• Do not overlook occult GI bleeding - it may be present without obvious symptoms 1
• Remember that young women may have low muscle mass, making creatinine an unreliable sole indicator of kidney function 5, 4
• Consider that multiple factors may coexist - dehydration plus high protein intake, for example 4

Management Approach

1. If dehydration is identified: Initiate appropriate fluid repletion and recheck BUN 5
2. If GI bleeding is suspected: Perform fecal occult blood testing and consider gastroenterology referral 1
3. If medication-related: Consider discontinuing or adjusting offending agents 1, 5
4. If high protein intake: Counsel on dietary modification and recheck labs 4

The answer is: All of the above - a comprehensive evaluation requires assessing for GI bleeding, steroid use, AND hypercatabolic states, as all can cause isolated BUN elevation in an otherwise healthy young adult.