Steroid-Induced Leukocytosis: Expected Magnitude and Patterns
Corticosteroid therapy typically causes a leukocytosis of up to 5 × 10⁹/L above baseline, with higher doses causing more significant elevations peaking at approximately 48 hours after administration.
Magnitude of Leukocytosis by Steroid Dose
The degree of leukocytosis following steroid administration is dose-dependent:
- Low-dose steroids: Mean increase of 0.3 × 10⁹/L in WBC count 1
- Medium-dose steroids: Mean increase of 1.7 × 10⁹/L in WBC count 1
- High-dose steroids: Mean increase of 4.84 × 10⁹/L in WBC count 1
- Chronic steroid treatment: In patients with acute infections, chronic steroid treatment can increase WBC counts by an average of 5 × 10⁹/L compared to non-steroid users 2
Timing and Pattern of Leukocytosis
- Peak effect: Leukocytosis typically peaks at 48 hours after steroid administration 1
- Onset: Can occur as early as the first day of treatment, especially with higher doses 3
- Duration: The elevated WBC count generally persists for the duration of therapy, though it may decrease somewhat after reaching maximal values (usually within two weeks) 3
- Long-term pattern: Even with prolonged treatment, WBC counts typically remain elevated above baseline but may decrease from peak values 3
Cellular Composition of Steroid-Induced Leukocytosis
Steroid-induced leukocytosis has a characteristic pattern:
- Predominant increase: Polymorphonuclear white blood cells (neutrophils) 3
- Associated changes:
- Monocytosis
- Eosinopenia
- Variable degree of lymphopenia 3
Differentiating Steroid-Induced Leukocytosis from Infection
When evaluating leukocytosis in a patient on steroids, consider these distinguishing features:
Steroid-induced leukocytosis:
- Rarely shows a significant "left shift" (>6% band forms)
- Typically lacks toxic granulation in neutrophils 3
- WBC increases proportional to steroid dose
- Predictable timing (peaks at ~48 hours)
Infection-related leukocytosis:
- Often shows left shift with >6% band forms
- May demonstrate toxic granulation in neutrophils
- WBC increases may exceed expected steroid-related elevation
- May be accompanied by other signs of infection (fever, localized symptoms)
Clinical Implications
- Any WBC increase exceeding 4.84 × 10⁹/L after high-dose steroids should raise suspicion for causes other than steroid effect alone 1
- Significant increases after low-dose steroids are less likely to be solely steroid-related 1
- In patients with suspected infection who are also on steroids, the expected steroid-induced increase (up to 5 × 10⁹/L) should be factored into the interpretation of WBC counts 2
Monitoring Recommendations
- Baseline CBC before initiating steroid therapy
- Follow-up CBC at 48-72 hours to assess peak effect
- Regular monitoring during prolonged therapy
- Consider more frequent monitoring if clinical suspicion for infection arises
Remember that even small doses of prednisone administered over prolonged periods can induce significant and persistent leukocytosis, which is particularly important to recognize when evaluating for potential infection in immunocompromised patients 3.