Interpretation and Workup of Neutrophilic Leukocytosis
This patient has moderate neutrophilic leukocytosis (WBC 14.5, ANC 9367) that warrants immediate evaluation for bacterial infection, as this WBC elevation (≥14,000 cells/mm³) carries a likelihood ratio of 3.7 for documented bacterial infection. 1
Immediate Interpretation
Your laboratory values show:
- WBC 14.5 × 10³/μL (elevated, threshold ≥14,000 has diagnostic significance) 1
- Absolute neutrophil count 9367/μL (elevated, indicating neutrophilia) 1
- Neutrophil percentage approximately 64% (calculated from ANC/WBC) - this is moderately elevated but does not reach the >90% threshold that carries the highest likelihood ratio (7.5) for serious bacterial infection 1
The most critical missing information is whether a left shift is present (band forms ≥16% or absolute band count ≥1,500 cells/mm³), as this has the highest diagnostic accuracy for bacterial infection with a likelihood ratio of 14.5 for absolute bands ≥1,500. 2, 3
Essential First Steps
1. Obtain Manual Differential Count Immediately
- Automated analyzers cannot reliably assess band forms and immature neutrophils - you must request a manual differential 2, 3
- Look specifically for:
2. Assess for Signs of Severe Infection/Sepsis
Examine immediately for: 2
- Temperature >38°C or <36°C
- Hypotension <90 mmHg systolic or drop >40 mmHg from baseline
- Tachycardia, tachypnea, altered mental status
- Hyperlactatemia >3 mmol/L, oliguria <30 ml/h
If any of these are present, initiate broad-spectrum empiric antibiotics within 1 hour and begin aggressive fluid resuscitation. 2
Systematic Infection Source Evaluation
Identify the Infection Source by Symptoms: 1, 2
Respiratory tract:
- Cough, dyspnea, chest pain → obtain pulse oximetry and chest X-ray 3
Urinary tract:
- Dysuria, flank pain, frequency → urinalysis for leukocyte esterase/nitrite and microscopy; if pyuria present, obtain urine culture 3
Skin/soft tissue:
- Erythema, warmth, purulent drainage → consider needle aspiration if fluctuant areas present 3
Gastrointestinal:
- Diarrhea, abdominal pain → assess volume status, consider stool studies including C. difficile if colitis symptoms present 3
Diagnostic Workup Algorithm
If Patient is Hemodynamically Stable: 2
- Blood cultures (2 sets from separate sites if systemic infection suspected) 1, 3
- Site-specific cultures based on suspected source 1
- Imaging directed at suspected infection source 1
- Complete diagnostic workup BEFORE starting antibiotics 2
If Patient Has Severe Sepsis/Septic Shock: 2
- Initiate broad-spectrum antibiotics within 1 hour (do NOT delay for cultures)
- Obtain blood cultures immediately before first antibiotic dose
- Aggressive fluid resuscitation
- Source control measures (drain abscesses, remove infected catheters)
- Vasopressor support if hypotension persists despite fluids
Non-Infectious Causes to Consider
Before attributing neutrophilia solely to infection, exclude: 1, 4
- Medications: lithium, beta-agonists, epinephrine
- Physiologic stress: recent surgery, exercise, trauma, emotional stress
- Smoking, obesity
- Chronic inflammatory conditions
- Asplenia
Critical Pitfalls to Avoid
- Do NOT ignore this WBC elevation even if the patient is afebrile - left shift can indicate bacterial infection without fever 1, 3
- Do NOT rely on automated differential alone - manual count is mandatory for accurate band assessment 2, 3
- Do NOT delay antibiotics in severe sepsis while awaiting culture results 2
- Do NOT treat asymptomatic patients with antibiotics based solely on lab values - clinical correlation is essential 2
- Do NOT overlook left shift when total WBC is only mildly elevated - this combination still indicates significant bacterial infection 3
When to Consider Hematology Referral
If bacterial infection is excluded and neutrophilia persists, consider referral if patient has: 4
- Fever, weight loss, bruising, or fatigue suggesting hematologic malignancy
- Persistent leukocytosis without identifiable cause
- Dysplastic features on peripheral smear