Neutrophils are white blood cells, a key part of the body’s defense system. Glucocorticoid steroids can increase neutrophil levels. This article explores why this happens and its implications.
Understanding Neutrophils
Neutrophils are the most numerous white blood cells, making up 50-70% of circulating leukocytes. They form in the bone marrow and have a multi-lobed nucleus and granular appearance. Their primary function is as a rapid first line of defense in the innate immune system against invading microbes, especially bacteria and fungi.
These cells quickly migrate from the bloodstream to sites of injury or infection. Once there, neutrophils recognize and engulf harmful microorganisms through phagocytosis. They also release antimicrobial substances and enzymes to neutralize threats. Historically seen as short-lived, non-specific cells, they are now recognized for their broader role in shaping the immune response and maintaining balance.
How Steroids Influence Neutrophil Levels
Glucocorticoid steroids (e.g., prednisone, dexamethasone, methylprednisolone) elevate neutrophil counts. This effect, known as steroid-induced neutrophilia, results from several mechanisms. The primary contributor is demargination, accounting for about 61% of the increase.
Demargination occurs because neutrophils normally adhere to the inner walls of blood vessels, forming a “marginated pool.” Glucocorticoids cause these neutrophils to detach from the endothelial surface and re-enter the main circulation. This happens because glucocorticoids reduce the expression of adhesion molecules like L-selectin on the neutrophil surface, responsible for their attachment.
Another mechanism is the delayed programmed cell death, or apoptosis, of neutrophils. Steroids prolong neutrophil lifespan, keeping them in circulation longer. Dexamethasone, for instance, can more than double their half-life. This delay accounts for about 29% of the increase.
Glucocorticoids reduce neutrophil movement from the bloodstream into tissues. This inhibition means fewer neutrophils leave circulation to enter inflamed areas, maintaining a higher concentration in the blood. Glucocorticoids also stimulate the bone marrow to produce and release more neutrophils, including immature forms. This contributes about 10% to the overall increase.
Implications of Elevated Neutrophil Counts
An elevated neutrophil count from steroid use is a common, expected side effect, often not indicating infection. This condition, called steroid-induced neutrophilia, is a direct pharmacological effect of glucocorticoids. Healthcare providers are aware of this and consider it when interpreting blood test results for patients on steroid therapy.
The increase in circulating neutrophils from steroid use involves mature forms, with only a small increase in immature “band” neutrophils. This differs from neutrophilia caused by bacterial infection, which often shows a significant increase in immature neutrophils, a pattern called a “left shift.” Patients with steroid-induced neutrophilia do not experience fever or worsening clinical symptoms, which helps distinguish it from an infection.
While an elevated neutrophil count is an expected response to steroid treatment, it is temporary and resolves once steroid medication is discontinued. The degree of elevation can be dose-dependent; higher steroid doses may lead to more significant increases. Though benign, significant or persistent elevations might prompt further evaluation by a healthcare professional to rule out other underlying conditions.