What does a slightly elevated white blood cell (WBC) count and neutrophils on a complete blood count (CBC) indicate?

Slightly Elevated White Blood Cell Count and Neutrophils: Clinical Significance

A slightly elevated white blood cell (WBC) count and neutrophils on a complete blood count (CBC) strongly suggests an underlying bacterial infection and warrants careful clinical assessment, even in the absence of fever. 1, 2

Clinical Significance of Elevated Neutrophils and WBCs

• An elevated WBC count (≥14,000 cells/mm³) has a likelihood ratio of 3.7 for detecting documented bacterial infection, making it a valuable indicator of possible infection 2, 1
• An elevated total band neutrophil count (≥1500 cells/mm³) has the highest likelihood ratio (14.5) for detecting bacterial infection, making it an even stronger indicator than total WBC count alone 2, 1
• An increase in the percentage of neutrophils (>90%) has a likelihood ratio of 7.5 for bacterial infection, providing additional diagnostic value 1
• A left shift (≥16% band neutrophils) has a likelihood ratio of 4.7 for bacterial infection, even with a normal total WBC count 2, 1

Common Causes of Neutrophilia

Infectious Causes

• Bacterial infections are the most common cause of neutrophilia, particularly:
  • Respiratory tract infections 1
  • Urinary tract infections 1
  • Skin/soft tissue infections 1
  • Gastrointestinal infections 1

Non-Infectious Causes

• Medications (lithium, beta-agonists, epinephrine) 1
• Physical or emotional stress 3
• Surgery or trauma 3
• Exercise 3
• Smoking 3
• Obesity 3
• Chronic inflammatory conditions 3
• Asplenia 3

Diagnostic Approach

• A CBC with differential should be performed for all patients suspected of having infection within 12-24 hours of symptom onset 2
• A manual differential is preferred to accurately assess bands and other immature forms 2, 1
• When evaluating slightly elevated WBCs and neutrophils:
  • Look for left shift (percentage of band neutrophils >16% or total band count >1,500/mm³) which strongly indicates bacterial infection 2, 1
  • Consider the neutrophil percentage, as it has better discriminatory power (AUROC 0.74) than absolute neutrophil count (0.63) or total WBC count (0.58) 4
  • Remember that the probability of bacteremia increases exponentially as neutrophil percentage rises from 80% to 100% 4

Clinical Management Algorithm

1. Initial Assessment:

   • Carefully examine for potential sources of infection (respiratory, urinary, skin/soft tissue, abdominal) 5
   • Consider that bacterial infection can present with leukocytosis alone, even without fever 5

2. Further Evaluation:

   • If infection is suspected despite initial negative tests, consider occult infection sites 6
   • Consider specialized testing for potential sources:
     • Intra-abdominal infections (CT imaging) 6
     • Endocarditis (echocardiography) 6
   • Blood cultures if fever or signs of sepsis are present 5

3. Management:

   • If bacterial infection is strongly suspected, initiate appropriate empiric antimicrobial therapy based on the likely source 6, 5
   • Obtain site-specific cultures before starting antibiotics when possible 5
   • Monitor with serial WBC counts to track response to therapy 6

Important Caveats and Pitfalls

• Avoid dismissing leukocytosis in the absence of fever - bacterial infection can present with leukocytosis alone 5
• Avoid treating asymptomatic patients with antibiotics based solely on mildly elevated WBC counts 6
• Remember that in the absence of fever, leukocytosis, left shift, or specific clinical manifestations of a focal infection, additional diagnostic tests may have low yield 2
• Consider that time-series data of left shift and WBC count reflect real-time neutrophil consumption during bacterial infection, so a single measurement may not be sufficient 7
• The neutrophil count is generally more informative than the neutrophil percentage for detecting neutrophilia and monitoring recovery 8