Concern for Infection Based on CBC with Differential
Yes, this CBC with differential raises significant concern for bacterial infection and warrants immediate clinical evaluation and likely empiric antibiotic therapy. The combination of leukocytosis (WBC 15.3), marked neutrophilia (80.3% with absolute count 12.3), and presence of immature granulocytes indicates an active left shift consistent with bacterial infection 1, 2.
Key Diagnostic Findings Supporting Infection
Leukocytosis with Left Shift
- The WBC count of 15.3 x 10³/μL exceeds the threshold of 14,000/mm³, which has a likelihood ratio of 3.7 for bacterial infection 1, 3
- The absolute neutrophil count of 12.3 x 10³/μL is markedly elevated, representing 80.3% of total WBCs, which when >90% has a likelihood ratio of 7.5 for bacterial infection 1
- Immature granulocytes are present at 1.2% (absolute 0.2 x 10³/μL), which predicts microbial infection, its invasiveness, and severity in critically ill patients 4
Clinical Significance of Immature Granulocytes
- The presence of immature granulocytes, even at this relatively modest percentage, is a useful marker comparable to C-reactive protein for predicting infection and its severity 4
- Immature granulocytes increase with increasing invasiveness and severity of infection, and their presence helps predict bloodstream infection and septic shock 4
Immediate Clinical Actions Required
Assess for Fever and Focal Infection Signs
- Check for fever patterns: temperature >100°F (37.8°C), ≥2 readings >99°F (37.2°C), or 2°F (1.1°C) increase from baseline 1, 2
- Evaluate for focal infection symptoms including respiratory symptoms (cough, dyspnea), urinary symptoms (dysuria, gross hematuria, new incontinence), skin/soft tissue changes, gastrointestinal symptoms, or altered mental status 1, 2
Obtain Diagnostic Studies
- Obtain blood cultures immediately before starting antibiotics, as the elevated neutrophil count and immature granulocytes significantly increase the likelihood of bloodstream infection 2
- Perform site-specific cultures based on symptoms: urinalysis with culture for urinary symptoms, sputum culture and chest imaging for respiratory symptoms, wound cultures for skin/soft tissue findings 2
- Manual differential is strongly preferred over automated methods to accurately assess band forms and other immature neutrophils 1, 2, 3
Consider Empiric Antibiotic Therapy
- Start empiric antibiotics if fever or focal infection signs are present, particularly given the high clinical suspicion for Gram-negative bacteremia with this degree of leukocytosis and left shift 2
- The Infectious Diseases Society of America recommends empiric antibiotics when there is leukocytosis with left shift plus fever or focal infection signs 2
Additional Considerations
Concurrent Anemia and Thrombocytosis
- The severe anemia (Hgb 8.0, Hct 24.2) with normocytic indices (MCV 88.3) may represent anemia of inflammation in the setting of acute infection 5
- The elevated platelet count (402 x 10³/μL) is consistent with reactive thrombocytosis, which commonly occurs with infection and inflammation 6
- However, the combination of leukocytosis, anemia, and thrombocytosis should also prompt consideration of primary bone marrow disorders if infection is ruled out 6
Monitoring and Follow-up
- Serial band counts and immature granulocyte percentages can guide antibiotic duration and response to therapy 2
- Persistent elevation despite treatment should prompt re-evaluation for inadequate source control, resistant organisms, or alternative diagnoses 2
Critical Pitfall to Avoid
Do not delay diagnostic workup or antibiotic therapy while waiting for additional test results if the patient appears clinically ill, as leukocytosis with immature granulocytes predicts severe infection including bloodstream infection and septic shock 4. The presence of immature granulocytes adds early diagnostic value and should not be dismissed even at relatively low percentages 4.