What variation in total white blood cell count can be expected in a 4-year-old child 2 days after completing a 3-day course of Omnocortil (prednisolone) for a wheezing episode, and how can it be differentiated from an actual infection?

Corticosteroid-Induced Leukocytosis in a 4-Year-Old After Omnocortil

A 4-year-old child tested 2 days after completing a 3-day course of prednisolone (Omnocortil) for wheezing can show a white blood cell count elevation of up to 4.84 × 10⁹/L (4,840 cells/μL) above baseline, with peak elevation occurring at 48 hours post-administration, and this must be differentiated from infection by examining the differential count pattern and clinical context.

Expected WBC Variation After Prednisolone

The magnitude of leukocytosis depends on the corticosteroid dose administered:

• High-dose steroids (typically >1 mg/kg/day prednisolone): Mean increase of 4.84 × 10⁹/L at 48 hours 1
• Medium-dose steroids (0.5-1 mg/kg/day): Mean increase of 1.7 × 10⁹/L 1
• Low-dose steroids (<0.5 mg/kg/day): Mean increase of 0.3 × 10⁹/L 1

For a typical 3-day course of prednisolone for pediatric wheezing (usually 1-2 mg/kg/day), you should expect a moderate to high elevation in the range of 1.7-4.84 × 10⁹/L above the child's baseline 1. The peak effect occurs at 48 hours after the last dose, which aligns perfectly with your timing of CBC testing 2 days post-completion 1.

Differentiating Steroid Effect from Infection

Steroid-Induced Leukocytosis Pattern:

• Neutrophilia with left shift absent: Corticosteroids cause mature neutrophil demargination without immature forms (bands, metamyelocytes) 1
• Lymphopenia: Steroids redistribute lymphocytes from circulation to lymphoid tissue 1
• Eosinopenia: Corticosteroids suppress eosinophil release and promote apoptosis 1
• Normal to slightly elevated monocytes: No significant toxic granulation 1

Infection-Induced Leukocytosis Pattern:

• Left shift present: Increased bands (>10%), metamyelocytes, or toxic granulation indicate active infection
• Lymphocytosis or normal lymphocytes: Especially in viral infections
• Eosinophils normal or elevated: Not suppressed as with steroids
• Clinical correlation: Fever, increased respiratory distress, new infiltrate on imaging, elevated inflammatory markers (CRP, procalcitonin)

Practical Algorithm for Interpretation

Step 1: Calculate the magnitude of elevation

• If WBC increase is ≤4.84 × 10⁹/L from baseline → Consistent with steroid effect 1
• If WBC increase is >4.84 × 10⁹/L → Consider infection or other pathology 1

Step 2: Examine the differential count

• Neutrophilia WITHOUT left shift + lymphopenia + eosinopenia → Steroid effect 1
• Neutrophilia WITH left shift (bands >10%) or toxic granulation → Infection likely
• Lymphocytosis → Viral infection more likely than steroid effect

Step 3: Clinical assessment

• Improving clinically (less wheezing, no fever, better activity) → Steroid effect most likely 2
• Worsening or new symptoms (persistent fever >3 days, increased work of breathing, new infiltrate) → Consider bacterial superinfection

Critical Pitfalls to Avoid

• Do not assume any WBC elevation is infection: Even substantial elevations up to 4.84 × 10⁹/L can be purely steroid-related at 48 hours 1
• Do not ignore the differential: The absolute WBC count alone is insufficient; the differential pattern is diagnostic 1
• Do not overlook timing: Steroid effect peaks at 48 hours and should begin declining thereafter; persistent elevation beyond 72-96 hours suggests alternative etiology 1
• Do not use low-dose steroid data for high-dose scenarios: Any increase after low-dose steroids (<0.5 mg/kg/day) should prompt investigation for other causes, as expected elevation is minimal (0.3 × 10⁹/L) 1

Additional Considerations for This Clinical Scenario

Since this child received prednisolone for wheezing, the underlying condition was likely viral-induced bronchospasm or early asthma 2, 3. The 3-day course is standard for acute exacerbations 2, 4. If the child is clinically improving with resolution of wheezing and no fever, the elevated WBC is almost certainly steroid-induced 1. However, if fever persists, respiratory symptoms worsen, or new infiltrates appear on chest imaging, bacterial pneumonia should be considered despite the recent steroid use 2.

Monitor for resolution: The WBC should normalize within 3-5 days after steroid discontinuation 1. Persistent elevation beyond this timeframe warrants further investigation.