What does an elevated absolute neutrophil count (ANC) on a complete blood count (CBC) indicate in an older adult patient?

What Does an Elevated Absolute Neutrophil Count Mean on a CBC?

An elevated absolute neutrophil count (ANC) on a CBC is a strong indicator of underlying bacterial infection and warrants immediate clinical assessment, even in the absence of fever. 1, 2

Diagnostic Significance and Likelihood of Bacterial Infection

The elevation in ANC provides quantifiable evidence for bacterial infection with specific likelihood ratios that guide clinical decision-making:

• WBC count ≥14,000 cells/mm³ carries a likelihood ratio of 3.7 for bacterial infection 1, 2, 3
• Neutrophil percentage >90% has a likelihood ratio of 7.5 for bacterial infection 3
• Left shift (≥16% band neutrophils) carries a likelihood ratio of 4.7 for bacterial infection, even when total WBC is normal 1, 3, 4
• Absolute band count ≥1,500 cells/mm³ has the highest likelihood ratio of 14.5 for documented bacterial infection 1, 2, 3

The presence of leukocytosis or left shift warrants careful assessment for bacterial infection in any patient with suspected infection, with or without fever. 1

Essential Immediate Workup

When you encounter an elevated ANC, you must obtain a manual differential count (not just automated analyzer results) to assess for band forms and other immature neutrophils—this is mandatory for accurate diagnosis. 1, 2, 4

Calculate the absolute band count immediately: multiply the total WBC by the percentage of bands. If this reaches ≥1,500 cells/mm³, you have the most powerful predictor of bacterial infection available. 1, 2, 3

Site-Specific Diagnostic Testing

Direct your workup based on clinical presentation:

• Respiratory symptoms (cough, dyspnea, chest pain): Obtain chest radiography and pulse oximetry 2, 4
• Urinary symptoms (dysuria, frequency, flank pain): Perform urinalysis with leukocyte esterase/nitrite testing and microscopic examination; if pyuria present, obtain urine culture 1, 2, 4
• Skin/soft tissue findings (erythema, warmth, purulent drainage): Consider needle aspiration or deep-tissue biopsy only if unusual pathogens suspected, fluctuant areas present, or initial treatment unsuccessful 1, 4
• Gastrointestinal symptoms (abdominal pain, diarrhea, peritoneal signs): Evaluate volume status and consider stool studies including C. difficile if colitis symptoms present 3, 4

Systemic Infection Assessment

Obtain blood cultures if any of the following are present: 2

• Fever >38°C or hypothermia <36°C
• Hypotension (systolic BP <90 mmHg)
• Tachycardia or tachypnea
• Altered mental status
• Lactate >3 mmol/L (indicates severe sepsis requiring immediate intervention)

Management Algorithm

If the patient is hemodynamically stable: Complete the diagnostic workup first before initiating antibiotics. 2

If sepsis criteria are present: Initiate broad-spectrum empiric antibiotics within 1 hour of recognition, along with aggressive fluid resuscitation. 2 Do not delay antibiotics while awaiting culture results in severe sepsis or septic shock. 2

Implement source control measures immediately (drainage of abscesses, removal of infected catheters). 2

Non-Infectious Causes to Consider

While bacterial infection is the primary concern, certain medications can cause neutrophilia: 3

• Lithium
• Beta-agonists
• Epinephrine

Myelodysplastic syndromes can also show left shift as a dysplastic feature in granulocytopoiesis. 4

Critical Pitfalls to Avoid

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. 2, 3, 4 This is one of the most commonly missed diagnoses.

Do not rely on automated analyzer alone—manual differential is essential to assess band forms and immature neutrophils. 1, 2, 4 Automated analyzers frequently miss significant left shifts.

Do not treat asymptomatic, hemodynamically stable patients with antibiotics based solely on laboratory findings without clinical correlation. 2, 3

Do not delay antibiotics in severe sepsis/septic shock while awaiting culture results. 2

Special Considerations in Older Adults

In older adults, particularly those in long-term care facilities, elevated ANC has particular diagnostic importance because: 1, 4

• Basal body temperature decreases with age, making fever less likely
• Typical symptoms and signs of infection are frequently absent
• Leukocytosis has been associated with increased mortality in nursing home-acquired pneumonia and bloodstream infections 1

In the absence of fever, leukocytosis, left shift, or specific clinical manifestations of focal infection, additional diagnostic tests may not be indicated due to low potential yield—however, nonbacterial infections cannot be excluded. 1, 4