What does an elevated Segmented Neutrophil (Seg) absolute count indicate on a White Blood Cell (WBC) differential (diff)?

Elevated Segmented Neutrophil Absolute Count: Diagnostic Significance

An elevated segmented neutrophil (seg) absolute count on a white blood cell (WBC) differential most strongly indicates bacterial infection, with likelihood ratios of 3.7 for WBC >14,000 cells/mm³ and 7.5 for neutrophils >90% of total WBCs. 1

Clinical Significance of Neutrophilia

Neutrophilia (elevated neutrophil count) can be caused by several conditions:

• Bacterial infections: Most common and significant cause
• Inflammatory conditions: Chronic inflammatory diseases
• Physiological stress: Surgery, trauma, exercise, emotional stress
• Medications: Corticosteroids, epinephrine, lithium
• Other conditions: Smoking, obesity, asplenia

Diagnostic Value

The combination of elevated WBC count with neutrophil predominance provides much stronger evidence for bacterial infection than either finding alone 1. This is particularly important in the context of sepsis diagnosis, where marked leukocytosis (>15,000/μL) with a left shift (band neutrophils >20% of leukocytes) is considered a criterion for severe sepsis 1.

Interpretation in Clinical Context

When evaluating an elevated segmented neutrophil count:

1. Consider the degree of elevation:

   • Mild elevation may occur with stress or inflammation
   • Marked elevation (>15,000/μL) strongly suggests bacterial infection 1

2. Look for accompanying findings:

   • Presence of toxic granulation in neutrophils appears to be as sensitive as absolute neutrophil count in predicting bacterial infections 2
   • Band count (immature neutrophils) has greater sensitivity in infants and elderly patients 2

3. Assess for clinical signs of infection:

   • Fever (>100°F/37.8°C or increase of 2°F/1.1°C over baseline)
   • Localized symptoms of infection
   • Vital sign abnormalities (tachycardia, hypotension, tachypnea)

Pitfalls and Caveats

• Single time-point limitation: A single elevated neutrophil count may not be diagnostic, as changes occur dynamically during the course of infection 3
• False negatives: Low or normal values do not rule out bacterial infection, as sensitivity is relatively low at all cut-off levels 4
• High specificity: High neutrophil counts (>15.0 x 10^9/L) have excellent specificity (97%) for bacterial infection 4
• Non-infectious causes: Remember that neutrophilia can be caused by non-infectious conditions including stress, medications, and chronic inflammatory conditions 5, 6

Clinical Application

For a patient with elevated segmented neutrophil count:

• Perform targeted assessment for sources of infection based on any accompanying symptoms
• Consider blood cultures if sepsis is suspected, especially with indwelling catheters 1
• Monitor for organ dysfunction as a complication of severe infection
• Consider empiric antibiotics only after appropriate cultures and in the presence of systemic illness signs 1
• Track neutrophil counts over time as they may provide more valuable information about the course of infection than single measurements 3

Remember that clinical signs and symptoms should guide diagnosis, not laboratory values alone 1. The combination of clinical presentation with laboratory findings provides the most accurate assessment of a patient's condition.