From the Research
A leukemoid reaction typically resolves within 1 day to several weeks after the underlying cause is treated, with the median duration being around 1 day, but it can be prolonged in some cases, especially in those with severe infections or other critical conditions, as seen in a study of 173 adult patients 1. The resolution timeframe can vary significantly depending on the specific trigger, such as severe infection, inflammation, malignancy, or medication reaction.
- For bacterial infections, appropriate antibiotic therapy may lead to normalization of white blood cell counts within days to a week.
- For medication-induced reactions, discontinuation of the offending drug usually results in resolution within 1-2 weeks.
- Inflammatory conditions may take longer to resolve, sometimes requiring 2-4 weeks or more depending on treatment response. Regular complete blood count monitoring is essential during recovery to ensure the white blood cell count is trending toward normal levels (typically below 11,000 cells/μL). The persistence of elevated counts beyond the expected resolution timeframe should prompt further investigation for occult infection, malignancy, or other underlying disorders that might have been missed in the initial evaluation, as supported by a more recent study of 267 cases with white blood cell count of >50 × 10^9/L, which found that infection was the most common cause of leukemoid reaction, and that lower hemoglobin, older age, and increased segmented neutrophil count were associated with increased risk of death 2. It's also important to note that the prognosis of patients with leukemoid reaction depends mainly on their underlying illness, and that a leukemoid reaction can be a sign of a serious underlying condition, such as sepsis or malignancy, which requires prompt and effective treatment to improve outcomes, as highlighted in a study of 758 nonhematologic cancer patients with extreme leukocytosis, which found that patients with paraneoplastic leukemoid reactions had a poor prognosis unless they received effective antineoplastic therapy 3.