What is the cause of reactive leukocytosis (increased white blood cell count) following vomiting?

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From the Guidelines

Reactive leukocytosis post vomiting is a temporary and benign condition that does not require specific treatment, and the primary focus should be on managing the underlying cause of vomiting. The condition is characterized by a temporary elevation in white blood cell count as a physiological response to the stress of vomiting, which typically resolves on its own once the underlying cause is addressed 1. For patients experiencing reactive leukocytosis post vomiting, the management strategy should include:

  • Treating the cause of vomiting with appropriate antiemetics
  • Maintaining hydration through oral rehydration solutions or IV fluids
  • Monitoring the trend of white blood cell counts through serial complete blood counts The leukocytosis occurs due to the release of stress hormones like epinephrine and cortisol during vomiting, causing demargination of white blood cells from the vessel walls into circulation 1. This is a normal physiological response, typically showing neutrophil predominance without left shift, and white blood cell counts usually normalize within 24-48 hours after vomiting resolves 1. If leukocytosis persists beyond this timeframe, further evaluation for underlying infection or other causes should be considered, and laboratory tests such as complete blood count, serum creatinine, and inflammatory markers like C-reactive protein, procalcitonin, and lactates may be useful in assessing the severity of the disease 1.

From the Research

Reactive Leukocytosis Post Vomiting

  • Reactive leukocytosis is a common condition characterized by an increase in white blood cell count, often in response to infection, inflammation, or physical stress 2.
  • Vomiting can be a cause of physical stress, leading to an increase in white blood cell count, although there is no direct evidence in the provided studies to support this specific claim.
  • The normal reaction of bone marrow to infection or inflammation leads to an increase in the number of white blood cells, predominantly polymorphonuclear leukocytes and less mature cell forms (the "left shift") 2.
  • Leukocytosis can be caused by various factors, including infections, inflammatory processes, physical stress, and emotional stress 2, 3.

Clinical Assessment and Diagnosis

  • A thorough history, physical examination, and peripheral blood smear are the basis of the initial evaluation for leukocytosis 3.
  • Constitutional symptoms along with an abnormal peripheral blood smear result indicate the need for evaluation for malignancy 3.
  • Patients with chronic leukemias usually present with less severe symptoms than patients with acute leukemias 3.

Management and Treatment

  • Oral rehydration therapy is a first-line treatment for mild to moderate dehydration, and ondansetron has proven to be a safe and effective adjunct in children with vomiting 4.
  • There is no direct evidence in the provided studies to support the management and treatment of reactive leukocytosis post vomiting.
  • Traditional management of nausea and vomiting has relied on pharmacotherapy, but many of the medications used have significant side effect profiles, making the need for new and improved interventions of great importance 5.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Leukocytosis: basics of clinical assessment.

American family physician, 2000

Research

Nausea and Vomiting in 2021: A Comprehensive Update.

Journal of clinical gastroenterology, 2021

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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