Neutropenia is characterized by a significant reduction in neutrophils, an essential first line of defense against infections. The main complication of neutropenia is the increased risk of an infection and the lack of resources to fight it off.
There are a number of causes of neutropenia including nutrient deficiency and genetic disorders. Most commonly, cancer patients develop neutropenia due to chemotherapy; the drugs involved destroy the neutrophils alongside the cancer cells.
In this article, we will discuss the causes, symptoms and treatments of neutropenia.
Contents of this article:
Fast facts on neutropenia
Here are some key points about neutropenia. More detail and supporting information is in the main article.
- In health, neutrophils are the most abundant type of white blood cell
- Neutropenia describes a condition where neutrophils are dangerously low in number
- Individuals with neutropenia are more likely to pick up serious infections
- One of the most common causes of neutropenia is chemotherapy
- There are a number of types of neutropenia, including cyclic neutropenia and chronic idiopathic neutropenia
- Often, there are no particular symptoms other than a heightened risk of infection
- Febrile neutropenia is regarded as a medical emergency
- Individuals with neutropenia must take extra precautions to avoid infection.
What are neutrophils?
Neutrophils are the most abundant type of white blood cell. They are normally the first cells of the immune system to reach the site of an infection. Neutrophils influence the inflammatory response to infection, ingest micro-organisms and destroy them by releasing enzymes.1
Neutrophils are produced in bone marrow, the spongy interior of the larger bones of the body. They are short-lived cells but highly mobile, being able to enter tissues that other cells cannot penetrate.2
Neutrophils are the primary constituent of pus and are responsible for its whitish-yellow hue.
What is neutropenia?
Neutropenia describes a reduction in neutrophils.
Neutropenia is a condition where there are abnormally low levels of neutrophils in the blood supply. Neutrophils are an important type of white blood cell, vital for fighting off pathogens, particularly bacterial infections.
In adults, a count of 1,500 neutrophils per μl of blood or less is considered to be neutropenia, with any count below 500 per μl of blood regarded as a severe case. In severe cases, even bacteria that are normally present in the mouth and gut can cause infections of a serious nature.3
Neutropenia can be caused by a decrease in neutrophil production, accelerated usage of neutrophils, increased destruction of neutrophils or a combination of all three factors.
Neutropenia can be temporary (acute) or long-lasting (chronic). The condition is also split into congenital (present from birth) and acquired neutropenia (develops later in life).
There are a number of types of neutropenia, including:
- Cyclic neutropenia: a rare congenital syndrome causing fluctuations in neutrophil numbers, it affects an estimated 1 in 1,000,000 people4
- Kostmann's syndrome: a genetic disorder where neutrophils are produced at lower levels - sufferers are prone to infections from an early age5
- Chronic idiopathic neutropenia: a relatively common version of neutropenia, predominantly affecting women
- Myelokathexis: a condition whereby neutrophils fail to move from the bone marrow to the bloodstream
- Autoimmune neutropenia: when an individual's immune system attacks and destroys neutrophils
- Shwachman's syndrome: a rare genetic disorder with multiple effects including dwarfism, problems with the pancreas and a low neutrophil count
- Isoimmune neonatal neutropenia: a condition whereby a mother's antibodies cross the placenta and attack the developing fetus' neutrophils. This condition generally resolves itself within 2 months of life.
Causes of neutropenia
Neutrophils are produced in the bone marrow at the center of larger bones. Anything that disrupts this process can cause neutropenia.
Most commonly, neutropenia is caused by chemotherapy for cancer. In fact, around half of cancer patients undergoing chemotherapy will experience some level of neutropenia.
Medical News Today asked Dr. Joel Newman, a consultant hematologist, why chemotherapy's attack on neutrophils is so significant for the immune system. He said:
"Chemotherapy affects all cells of the granulocytic lineage, but it is the neutrophils that are most important in acute bacterial infections, and so we are most vigilant when they are low.
When someone is neutropenic, severe infections can develop rapidly and become overwhelming in the space of minutes to hours. In contrast, having too few basophils or eosinophils will not expose you to much harm in the short term."6
Other potential causes of neutropenia include:
- Leukemia: a group of cancers of the blood
- Barth syndrome: an X-linked genetic disorder affecting multiple systems
- Myelodysplastic syndromes: a group of disorders characterized by dysfunctional blood cells7
- Myelofibrosis: a rare bone marrow cancer, also known as osteomyelofibrosis
- Alcohol use disorder: including alcoholism
- Vitamin deficiencies: most commonly, vitamin B12, folate and copper deficiency8
- Sepsis: an infection of the bloodstream that uses up neutrophils quicker than they can be produced
- Pearson syndrome: a mitochondrial disease
- Some infections: including hepatitis A, B and C, HIV/AIDS (human immunodeficiency virus/acquired immune deficiency syndrome), malaria and Lyme disease
- Rheumatoid arthritis: an autoimmune disorder
- Hypersplenism: an overactive spleen.
Premature babies are more likely to be born with neutropenia than babies born near their due date; the condition affects 6-8% of newborns in neonatal intensive care units. As a general rule, the smaller the baby, the more likely they are to have neutropenia.9
On the next page, we look at the symptoms and treatment of neutropenia.