What tests should be ordered for a patient with leukocytosis and neutrophilia?

Diagnostic Approach for a Patient with Leukocytosis and Neutrophilia

For a patient with WBC of 13.7K and absolute neutrophils of 9,563, a systematic evaluation for bacterial infection should be performed, including urinalysis, chest X-ray, and blood cultures if fever is present.

Understanding the Clinical Significance

The patient's laboratory values show:

• WBC count of 13.7K (mild leukocytosis)
• Absolute neutrophil count of 9,563 (neutrophilia)

These findings strongly suggest an inflammatory process, most likely bacterial infection. According to guidelines, leukocytosis with neutrophilia warrants careful assessment for bacterial infection even in the absence of fever 1.

Diagnostic Algorithm

Step 1: Assess for Clinical Signs of Infection

• Check for fever, chills, or hypothermia
• Look for specific symptoms pointing to an organ system (respiratory, urinary, skin, etc.)
• Evaluate for signs of sepsis or hemodynamic compromise

Step 2: Initial Laboratory Workup

1. Complete Blood Count with Manual Differential (already performed)

   • Examine for band forms (immature neutrophils)
   • A band count >10% has a specificity of 92% for infection 2
   • Left shift (percentage of band neutrophils >16%) has a likelihood ratio of 4.7 for bacterial infection 1

2. Urinalysis and Urine Culture

   • Indicated for all patients with unexplained leukocytosis 1
   • Should include leukocyte esterase and nitrite testing
   • Only proceed to urine culture if pyuria is present (≥10 WBCs/high-power field) 1

3. Inflammatory Markers

   • C-reactive protein (CRP)
   • Procalcitonin (particularly useful in distinguishing bacterial from non-bacterial causes) 1

Step 3: Imaging and Additional Tests Based on Clinical Suspicion

1. Chest X-ray

   • Recommended for patients with leukocytosis even without respiratory symptoms 1

2. Blood Cultures

   • Indicated if fever, chills, hypothermia, or signs of hemodynamic compromise are present 1
   • Should be collected before antibiotic administration when possible

3. Additional Site-Specific Testing based on symptoms:

   • Abdominal imaging if abdominal symptoms
   • Skin/soft tissue cultures if skin lesions present
   • Joint aspiration if joint pain/swelling

Special Considerations

• Elderly patients: May have blunted inflammatory response; leukocytosis >14,000 cells/mm³ has a likelihood ratio of 3.7 for bacterial infection 1

• Neutrophilia without fever: Still warrants investigation for bacterial infection as approximately 50% of elderly patients with documented bacterial infections may not present with fever 1

• Non-infectious causes: Consider medication effects, stress response, malignancy (especially if persistent leukocytosis after infection is ruled out)

Pitfalls to Avoid

1. Do not assume all leukocytosis is due to infection

   • Leukocytosis can be reactive to trauma, stress, medications, or malignancy

2. Do not rely solely on WBC count

   • The pattern of leukocytosis (neutrophilia with left shift) is more important than absolute numbers

3. Do not overlook non-bacterial causes

   • Viral infections typically cause lymphocytosis rather than neutrophilia
   • Parasitic infections may cause eosinophilia

4. Do not delay appropriate testing

   • Early diagnosis of infection source improves outcomes

By following this systematic approach, the underlying cause of the patient's leukocytosis and neutrophilia can be efficiently identified, allowing for appropriate targeted therapy.