Can dehydration cause leukocytosis (elevated white blood cell count)?

Can Dehydration Cause Leukocytosis?

Yes, dehydration can cause leukocytosis (elevated white blood cell count) due to hemoconcentration, where the reduction in plasma volume concentrates cellular blood components without an actual increase in the total number of white blood cells.

Mechanism of Dehydration-Induced Leukocytosis

• Dehydration reduces plasma volume while the total number of circulating white blood cells remains unchanged, resulting in an apparent increase in white blood cell concentration 1
• This hemoconcentration effect is similar to what occurs with other cellular blood components during dehydration 1
• The leukocytosis observed in dehydration is primarily a relative increase rather than an absolute increase in white blood cell production 1

Clinical Evidence

• Studies have demonstrated that thermal dehydration without exercise can increase leukocyte levels beyond what would be predicted by hemoconcentration alone 1
• Specific white blood cell populations may respond differently to dehydration, with some studies showing decreased eosinophil counts while other leukocyte types tend to increase 1
• Severe dehydration has been documented to cause marked leukocytosis in clinical cases 2

Clinical Implications

• When evaluating patients with leukocytosis, dehydration should be considered as a potential contributing factor 3, 4
• Rehydration may help normalize white blood cell counts in dehydrated patients 5
• Intravenous hydration (2.5-3 liters/m²/day) is recommended for patients with hyperleukocytosis, particularly in conditions like leukemia where it can help reduce complications 5

Management Considerations

• Hydration status should be assessed in all patients presenting with leukocytosis 4
• In patients with both dehydration and leukocytosis, rehydration should be initiated while investigating other potential causes of the elevated white blood cell count 6
• Patients with hyperleukocytosis due to conditions like leukemia should receive aggressive hydration as part of their initial management 5

Differentiating Causes of Leukocytosis

• When evaluating leukocytosis, consider both relative (dehydration) and absolute (infection, inflammation, malignancy) causes 3, 4
• Other common causes of leukocytosis include:
  • Infections (particularly bacterial) 3
  • Physical or emotional stress 3
  • Medications (corticosteroids, lithium, beta agonists) 3
  • Primary bone marrow disorders 3
• Extremely elevated white blood cell counts (>100,000 per mm³) are less likely to be due to dehydration alone and represent a medical emergency requiring immediate attention 3

Pitfalls and Caveats

• Failure to recognize dehydration as a cause of leukocytosis may lead to unnecessary diagnostic testing 4
• Conversely, attributing leukocytosis solely to dehydration may result in missed diagnoses of serious conditions 3
• When leukocytosis persists after adequate rehydration, further investigation for other causes is warranted 4
• In patients with both dehydration and conditions predisposing to hyperleukocytosis (such as leukemia), hydration alone may significantly reduce white blood cell counts 6