Can a humerus fracture cause leukocytosis (White Blood Cell (WBC) count elevation) in an elderly patient?

Can a Humerus Fracture Cause Leukocytosis in an Elderly Patient?

Yes, a humerus fracture can cause leukocytosis with a WBC of 14.6, but infection must be ruled out first, as bacterial infection is the most common and serious cause of neutrophilia in elderly patients.

Primary Consideration: Exclude Infection

The WBC count of 14.6 × 10⁹/L meets the threshold (≥14,000 cells/mm³) that warrants careful assessment for bacterial infection, even without fever 1, 2. In elderly patients, this is particularly critical because:

• Bacterial infections are the most common cause of neutrophilia and carry the highest morbidity and mortality risk 1
• Elderly patients frequently lack typical infection symptoms (fever, localized pain), making laboratory values more important for diagnosis 2
• Basal body temperature decreases with age and frailty, so classic fever definitions are unreliable in this population 2

Essential Diagnostic Steps

Obtain a manual differential count immediately to assess for left shift, which is the most powerful predictor of bacterial infection 1, 3:

• Absolute band count ≥1,500 cells/mm³ has the highest likelihood ratio (14.5) for bacterial infection 1, 3
• Band percentage ≥16% has a likelihood ratio of 4.7 for bacterial infection, even with normal total WBC 1, 3
• Neutrophil percentage >90% has a likelihood ratio of 7.5 for bacterial infection 1

Evaluate for specific infection sources based on clinical presentation 2, 3:

• Respiratory: Check for cough, dyspnea, hypoxemia; obtain pulse oximetry and chest radiography if indicated 2, 3
• Urinary: Assess for dysuria, new incontinence, gross hematuria; perform urinalysis if symptomatic 2, 3
• Skin/soft tissue: Examine the fracture site and surrounding tissues for erythema, warmth, drainage, or fluctuance 3
• Surgical site: If the fracture was surgically treated, evaluate for postoperative infection 3

Non-Infectious Causes of Leukocytosis

After excluding infection, consider these alternative causes:

Physiologic stress response from the fracture itself 4, 5:

• Physical trauma, surgery, and emotional stress can double the peripheral WBC count within hours due to demargination of neutrophils from bone marrow storage pools 4, 5
• This stress-induced leukocytosis is typically mild to moderate and resolves within 24-48 hours 5

Medications that commonly cause neutrophilia 1, 3:

• Corticosteroids (most common) 5
• Lithium 1, 3
• Beta-agonists 1, 3
• Epinephrine 1

Chronic conditions in elderly patients 4:

• Chronic inflammatory conditions 4
• Obesity 4
• Smoking 4

Clinical Algorithm

1. Review the manual differential (not automated) for left shift 1, 3
2. If left shift present (bands ≥16% or absolute band count ≥1,500): Strongly suspect bacterial infection; obtain blood cultures if bacteremia suspected, and site-specific cultures based on symptoms 3
3. If no left shift and WBC 14.6 with clinical signs of infection: Still investigate for infection source with targeted testing 1, 2
4. If no left shift and no infection symptoms: Consider stress response from fracture trauma; repeat CBC in 24-48 hours to assess trend 4, 5
5. If WBC remains elevated or rises: Expand workup for occult infection or other causes 4

Critical Pitfalls to Avoid

• Do not assume the fracture alone explains the leukocytosis without excluding infection first 1, 2
• Do not rely on fever alone to diagnose infection in elderly patients, as they often lack typical fever response 2
• Do not use automated differential alone—manual differential is essential for accurate band assessment 1, 3
• Do not ignore left shift when total WBC is only mildly elevated, as this combination still indicates significant bacterial infection 1, 3
• Do not overlook the fracture site itself as a potential source of infection, especially if there was open injury or surgical intervention 3

Bottom Line

While trauma from a humerus fracture can cause mild leukocytosis through physiologic stress response, a WBC of 14.6 in an elderly patient mandates evaluation for bacterial infection first because of the significantly higher morbidity and mortality risk 1, 2. The manual differential with assessment for left shift is the single most important next step to guide management 1, 3.