In a 58‑year‑old man with worsening confusion over several days, afebrile, no tachycardia, no urinary symptoms, an elevated white‑blood‑cell count, and a urine specific gravity of 1.030, what is the most likely cause of the leukocytosis and what is the immediate next step in management?

Acute Confusion with Leukocytosis in a 58-Year-Old Man

The most likely cause of leukocytosis in this patient is an occult bacterial infection, and the immediate next step is to obtain a manual differential count to assess for left shift (band forms), followed by targeted evaluation for infection sources including blood cultures, chest imaging, and comprehensive urinalysis with culture. 1, 2, 3

Immediate Diagnostic Priority: Manual Differential Count

• A manual differential count is mandatory to accurately assess band neutrophils, as automated analyzers are insufficient for detecting left shift 1, 2, 3
• An absolute band count ≥1,500 cells/mm³ has the highest likelihood ratio (14.5) for documented bacterial infection, even without fever 1, 3
• A band percentage ≥16% carries a likelihood ratio of 4.7 for bacterial infection 1, 3
• Left shift can occur with normal or mildly elevated WBC counts and still indicates serious bacterial infection requiring immediate evaluation 2, 3

Critical Clinical Assessment for Infection Source

Confusion as a presenting symptom warrants particular attention, as altered mental status may represent delirium from systemic infection in this age group 4:

• Evaluate for sepsis criteria: Check lactate level (>3 mmol/L indicates severe sepsis requiring immediate intervention), blood pressure, heart rate, and respiratory rate 1
• Respiratory evaluation: Obtain chest radiography to exclude pneumonia, as respiratory infections are common occult sources 3
• Blood cultures: Should be obtained given the combination of confusion and leukocytosis, as bacteremia must be excluded 1, 3
• Comprehensive urinalysis with microscopy and culture: Despite the absence of urinary symptoms, UTI remains a common occult source in adults and can present atypically with confusion 1, 3

Interpretation of the Urine Specific Gravity Finding

The urine specific gravity of 1.030 indicates concentrated urine, which has important diagnostic implications 5:

• Concentrated urine (specific gravity >1.030) reduces the diagnostic performance of urinalysis for detecting UTI, with positive likelihood ratios decreasing significantly compared to dilute urine 5
• This concentration level suggests possible dehydration, which itself may contribute to confusion 4
• If urinalysis shows only trace leukocytes without pyuria, this makes UTI unlikely as the primary source of systemic leukocytosis 1

Management Algorithm Based on Left Shift Results

If left shift is present (bands ≥1,500 or ≥16%):

• Initiate targeted search for bacterial infection source with blood cultures, chest radiography, and urinalysis with culture 1, 3
• If patient is hemodynamically stable, complete diagnostic workup before initiating antibiotics 1
• If sepsis criteria are present (hypotension, lactate >3 mmol/L, organ dysfunction), initiate broad-spectrum empiric antibiotics within 1 hour 1

If no left shift is present:

• The absence of left shift with normal vital signs and no fever makes acute bacterial infection less likely 2
• Consider alternative causes of confusion: metabolic derangements, medication effects, or non-infectious neurologic processes 4
• Monitor closely and reassess if clinical status changes 2

Critical Pitfalls to Avoid

• Do not ignore elevated band counts when total WBC is only mildly elevated—left shift is more predictive of bacterial infection than the total WBC count alone 1, 2, 3
• Do not rely on automated differential alone—manual differential is essential to accurately assess band forms 1, 2, 3
• Do not assume confusion is simply "delirium" without identifying the underlying cause—in a 58-year-old, new confusion with leukocytosis demands thorough infection workup 4, 1
• Do not treat asymptomatic bacteriuria if found—in older adults, bacteriuria prevalence is 15-50% and represents colonization rather than infection unless accompanied by systemic signs or pyuria 4, 2
• Do not delay antibiotics if severe sepsis/septic shock develops while awaiting culture results 1

Special Considerations for This Age Group

• Leukocytosis >17 × 10⁹/L may indicate infection even without fever 4
• A reactive leukocytosis from trauma or stress is possible, but the progressive confusion over several days makes infection more likely than an acute stress response 6
• The combination of confusion and leukocytosis in a middle-aged adult warrants aggressive evaluation, as mortality increases significantly with delayed recognition of bacterial infection 3