What is the appropriate evaluation and initial management for a 70‑year‑old patient with neutrophil‑predominant leukocytosis (white blood cell count 18.5 ×10⁹/L)?

Evaluation of a 70-Year-Old with Neutrophil-Predominant Leukocytosis (WBC 18.5)

This patient requires immediate assessment for bacterial infection with manual differential count, targeted infection workup based on clinical findings, and empiric antibiotics only if sepsis criteria are met or a clear infectious source is identified.

Immediate Diagnostic Workup

Manual Differential Count (Mandatory First Step)

• Order a manual 500-cell differential immediately to assess for left shift, as automated analyzers cannot reliably identify band forms and immature neutrophils 1, 2
• Calculate absolute band count: if ≥1,500 cells/mm³, this provides the highest likelihood ratio (14.5) for documented bacterial infection 1, 2
• Assess band percentage: if ≥16%, this yields a likelihood ratio of 4.7 for bacterial infection even when total WBC is only mildly elevated 1, 2
• Evaluate neutrophil proportion: if ≥90%, this confers a likelihood ratio of 7.5 for bacterial infection 1, 2

Critical Clinical Assessment

• Assess vital signs systematically: temperature >38°C or <36°C, systolic blood pressure <90 mmHg, heart rate >100 bpm, respiratory rate >20/min 1, 2
• Evaluate for altered mental status or new confusion, as this may be the sole manifestation of systemic bacterial infection in elderly patients 1, 2
• Examine for respiratory symptoms: cough, dyspnea, chest pain suggesting pneumonia 1
• Assess for urinary symptoms: dysuria, flank pain, frequency, new or worsening incontinence 1, 2
• Inspect skin and soft tissues: erythema, warmth, purulent drainage 1
• Perform abdominal examination: peritoneal signs, diarrhea suggesting intra-abdominal infection 1

Targeted Laboratory and Imaging Studies

• Obtain blood cultures (two sets from peripheral vein and any indwelling catheters) before antibiotics if bacteremia is suspected 3, 1
• Urinalysis with microscopy: order only if urinary symptoms are present; if pyuria is documented (≥10 WBCs per high-power field or positive leukocyte esterase), then obtain urine culture 1, 2
• Measure serum lactate: if >3 mmol/L, this indicates severe sepsis requiring immediate intervention 1
• Chest radiography: obtain if respiratory symptoms or hypoxemia are present 2
• Additional site-specific cultures based on suspected infection source 4

Management Algorithm

If Left Shift Is Present (≥16% Bands or ≥1,500 Cells/mm³ Absolute Bands)

• Initiate empiric broad-spectrum antibiotics immediately after obtaining appropriate cultures, even in the absence of fever 2, 4
• Base antibiotic selection on suspected infection source and local resistance patterns 2, 4
• Provide aggressive fluid resuscitation if hypotension is present 1
• Initiate vasopressor support if hypotension persists despite fluids 1
• Implement source control measures (drainage of abscesses, removal of infected catheters) 1

If No Left Shift and Patient Is Asymptomatic

• Do not pursue further laboratory or imaging investigations, as the diagnostic yield is low 2, 4
• Monitor clinically: repeat complete blood count with manual differential in 12–24 hours if clinical concern persists 2
• Do not initiate antibiotics based solely on laboratory findings without clinical correlation 1, 2

If Sepsis Criteria Are Met

• Initiate broad-spectrum empiric antibiotics within 1 hour of recognition 1, 4
• Administer aggressive fluid resuscitation for hypotension 1
• Escalate to vasopressor support if hypotension persists despite fluids 1

Special Considerations in This 70-Year-Old Patient

Age-Related Factors

• Older adults frequently lack typical infection symptoms such as fever; altered mental status or new confusion may be the only manifestation of systemic bacterial infection 1, 2
• Decreased basal body temperature in elderly patients means that absence of fever does not exclude bacterial infection 2
• Left shift has particular diagnostic importance in older adults due to atypical presentations 2

Asymptomatic Bacteriuria

• Do not obtain urinalysis or urine culture in truly asymptomatic patients, even with leukocytosis, as asymptomatic bacteriuria occurs in 15–50% of non-catheterized older adults and does not indicate infection 2
• In patients with chronic indwelling catheters, asymptomatic bacteriuria prevalence approaches 100%, reflecting colonization rather than infection 1, 2

Critical Pitfalls to Avoid

• Do not rely on automated analyzer alone: manual differential is essential to assess band forms and immature neutrophils 1, 2
• Do not ignore elevated neutrophil count when total WBC is only mildly elevated: left shift can occur with normal WBC and still indicate serious bacterial infection 1
• Do not delay antibiotics in severe sepsis/septic shock while awaiting culture results 1
• Do not treat based solely on laboratory findings without clinical correlation if patient is asymptomatic and hemodynamically stable 1, 2
• Do not attribute delirium to non-specific causes without thorough infection investigation in the setting of leukocytosis 1

Alternative Diagnoses to Consider

Non-Infectious Causes

• Medications: corticosteroids, lithium, beta-agonists can cause neutrophilia with left shift 2, 5, 6
• Physical or emotional stress: surgery, trauma, exercise can double peripheral WBC count within hours 5, 6
• Chronic inflammatory conditions, smoking, obesity, asplenia 5, 6

Hematologic Malignancies (Less Likely but Important)

• Suspect primary bone marrow disorders if extremely elevated WBC counts, concurrent red blood cell or platelet abnormalities, weight loss, bruising, hepatosplenomegaly, or lymphadenopathy are present 5, 6
• Chronic lymphocytic leukemia should be considered in this age group, though absolute lymphocyte count alone is not an indication for treatment unless >200–300 × 10⁹/L 3
• Refer to hematology/oncology if malignancy cannot be excluded or another more likely cause is not suspected 5