Is a shift to the left with neutrophilia (increased neutrophil count) an indication of bacterial infection?

Left Shift with Neutrophilia: Strong Indicator of Bacterial Infection

Yes, a left shift with neutrophilia is a strong indication of bacterial infection and warrants careful assessment for bacterial infection, with or without fever. 1

Diagnostic Accuracy of Left Shift Parameters

The quantitative thresholds that best predict bacterial infection, ranked by diagnostic power:

• Absolute band count ≥1,500 cells/mm³ has the highest likelihood ratio (14.5) for documented bacterial infection 1, 2, 3
• Neutrophil percentage ≥90% carries a likelihood ratio of 7.5 for bacterial infection 1, 4
• Band neutrophil percentage ≥16% (left shift) has a likelihood ratio of 4.7 for bacterial infection 1, 2, 3
• Total WBC count ≥14,000 cells/mm³ has a likelihood ratio of 3.7 1

Critical Clinical Point: Left Shift with Normal WBC

Do not ignore left shift when total WBC count is normal—this combination still indicates significant bacterial infection requiring evaluation. 1, 2, 3 The presence of a high percentage of neutrophils or left shift, even with a normal total leukocyte count (<10,000 cells/mm³), demonstrates high probability of underlying bacterial infection. 1

Essential Diagnostic Requirements

Manual Differential is Mandatory

• Manual differential count is essential—automated analyzers cannot reliably assess band forms and immature neutrophils 1, 2, 3
• Automated analyzer flags alone are insufficient for accurate band assessment 2, 3
• Manual examination by experienced technologists is required to identify band forms, toxic granulation, vacuolization, and Döhle bodies 5, 6

Morphologic Changes Add Diagnostic Value

• Toxic granulation in neutrophils is as sensitive as absolute neutrophil count in predicting bacterial infection 5
• Reactive morphologic changes (toxic granules, Döhle bodies, cytoplasmic vacuoles) have high sensitivity (80%) for inflammatory/infectious disease, though lower specificity 6

Clinical Assessment Algorithm

When left shift with neutrophilia is identified, systematically evaluate for:

Infection Source Identification

• Respiratory tract: cough, dyspnea, chest pain—obtain chest radiography if hypoxemia documented 2, 3
• Urinary tract: dysuria, flank pain, frequency—perform urinalysis for leukocyte esterase/nitrite; if pyuria present, obtain urine culture 1, 2, 3
• Skin/soft tissue: erythema, warmth, purulent drainage—consider needle aspiration or deep-tissue biopsy if fluctuant areas present or initial treatment unsuccessful 2, 3
• Gastrointestinal: evaluate volume status and stool examination for pathogens including C. difficile if colitis symptoms present 3

Severity Assessment

Indicators of severe infection/sepsis requiring immediate intervention:

• Fever >38°C or hypothermia <36°C 2
• Hypotension (<90 mmHg systolic or decrease >40 mmHg from baseline) 2
• Tachycardia, tachypnea, altered mental status 2
• Hyperlactatemia (>3 mmol/L), oliguria (<30 ml/h or <0.5 ml/kg/h) 2

Blood Culture Indications

Blood cultures should be obtained when: 1

• New fever or chills develop 1
• Hypothermia present 1
• Leukocytosis or left shift of neutrophils documented 1
• Neutropenia present 1
• Signs of hemodynamic compromise 1
• Hypoalbuminemia or development of renal failure 1

Blood should be obtained by fresh venipuncture immediately following onset of fever, as bacteria are rapidly cleared from blood and fever typically follows bacteremia by 30-90 minutes. 1

Management Approach

Severe Sepsis/Septic Shock

• Initiate broad-spectrum empiric antibiotics within 1 hour of recognition 2
• Aggressive fluid resuscitation for hypotension 2
• Source control measures (drainage of abscesses, removal of infected catheters) 2
• Vasopressor support if hypotension persists despite fluid resuscitation 2

Hemodynamically Stable Patients

• Complete diagnostic workup before antibiotics 2
• Initiate targeted antibiotic therapy based on suspected source and local resistance patterns 2, 3
• Close monitoring for clinical deterioration 2

Important Caveats and Common Pitfalls

When Left Shift May NOT Indicate Infection

• Myelodysplastic syndromes can show left shift as a dysplastic feature in granulocytopoiesis 3
• Medications including lithium, beta-agonists, and epinephrine can cause neutrophilia with left shift 2, 3, 4

Timing Considerations

Left shift does not occur in the extremely early or late phases of infection; therefore, assessing data from a single time point is unsuitable for diagnosing bacterial infection. 7 Time-series data of left shift and WBC count reflect real-time neutrophil consumption during the course of bacterial infection, allowing more accurate evaluation. 7

Special Populations

In older adults in long-term care facilities, left shift has particular diagnostic importance due to decreased basal body temperature and frequent absence of typical infection symptoms. 3 In this population, leukocytosis has been associated with increased mortality among residents with nursing home-acquired pneumonia (WBC ≥15,000 cells/mm³) and bloodstream infection (WBC ≥20,000 cells/mm³). 1

What NOT to Do

• Do not treat asymptomatic patients with antibiotics based solely on laboratory findings without clinical correlation 2, 3, 4
• Do not delay antibiotics in severe sepsis/septic shock while awaiting culture results 2
• Do not perform urinalysis and urine cultures for asymptomatic residents 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 1, 4