Key Takeaways

✅ Smoking is associated with leukocytosis.

✅ As a general rule the increase in white blood cell count is modest (<20%), with the total WBC count rarely exceeding 20 x 10⁹/L.

✅ All white blood cell (WBC) subtypes are affected, but the predominant effect is on neutrophils. 

✅ There is a dose response such that WBC counts are higher in heavy vs. lighter smokers. 

✅ Smoking cessation leads to a time-dependent reversal of leukocytosis, though there is a residual effect even years after stopping.