What Is Neutrophilia?

Neutrophilia is a condition where there are abnormally high numbers of neutrophils circulating in the blood. Neutrophils are a type of white blood cell that plays a key role in fighting infections, such as those caused by viruses, bacteria, and other pathogens.

Because neutrophils are white blood cells, people with too many neutrophils in their blood may develop leukocytosis, having an abnormally high total white blood cell count (more than 11,000 white blood cells per microliter of blood). This is important to detect because abnormal numbers of white blood cells (including neutrophils) often indicate there is an underlying health condition.

In adults, the normal range for neutrophils in the blood is typically between 2,500 to 7,000 neutrophils per microliter (µL) of blood. A neutrophil count higher than 7,700 per µL is generally considered neutrophilia.¹

The importance of neutrophils

Neutrophils are produced under a tightly regulated process in the bone marrow and are released into the bloodstream once they become mature. Although they are very powerful and efficient at fighting invading pathogens, they are very short-lived to prevent them from causing any possible damage to our own tissues. For this reason, they only last approximately 24 hours in your circulation before they die. 

They are the first cells recruited to the site of infection, are the cells most commonly found in inflamed tissues, and are also the main constituents of pus. They have different strengths and modes of action when it comes to killing microbes. Key functions of neutrophils include: 

1. Phagocytosis – neutrophils can engulf and break down bacteria, viruses, and other harmful microbes.
2. Toxic Molecule Release – toxic molecules can kill pathogens but may also damage healthy cells.
3. Neutrophil Extracellular Traps (NETs) – neutrophils can work together to produce nets that trap and immobilise pathogens, preventing their spread.^2,3

Neutrophilia as an indicator of underlying conditions

Neutrophilia can be caused by various factors. The most frequent causes are summarised below:¹

• Factitious Neutrophilia – due to a machine or test procedure error and often needs a repeat test
•  Primary Neutrophilia – due to bone marrow overproducing neutrophils without a previous stimulus 
• Secondary Neutrophilia – due to your bone marrow reacting to a stimulus and producing too many neutrophils, also known as reactive neutrophilia

Below are these possible causes explained in further detail.

What is factitious neutrophilia?

Factitious neutrophilia occurs when external or internal factors interfere with the test results, reporting a falsely high number of neutrophils. This can occur if samples are not properly handled or processed before examination. In such cases, a repeat test may be necessary.

What is primary neutrophilia?

Primary neutrophilia refers to an inherent or acquired condition that causes the bone marrow to produce an excessive number of neutrophils without an external stimulus such as in the case of leukaemia (cancer) patients. Some individuals may naturally produce higher levels of neutrophils due to genetic factors, where most patients do not have any negative health implications. 

However, in rare conditions, this can lead to recurrent infections and even become life-threatening. For example, this is the case for a rare condition most commonly diagnosed in children and neonates, known as leukocyte adhesion factor deficiency.

Other people develop neutrophilia due to a cancer or malignancy developing in their bone marrow, where neutrophils are produced. This can cause an overproliferation of neutrophils, a condition known as myeloproliferative neoplasms. Some malignancies associated with high neutrophil levels include chronic myeloid leukaemia, thrombocythemia, or chronic neutrophilic leukaemia. 

What is secondary neutrophilia?

Because secondary neutrophilia is characterised by having a previous stimulus, the most common cases are due to having a previous infection by bacteria and viruses. Other reasons behind secondary neutrophilia include having previous inflammatory diseases, such as rheumatoid arthritis, granulomatous disease, vasculitis, chronic hepatitis, and inflammatory bowel disease.

Other common causes of secondary neutrophilia include some adverse effects of medications. Some of these are listed below:

• Granulocyte-stimulating factors such as G-CSF and GM-CSF – medications which stimulate your bone marrow to produce more neutrophils. 
• Glucocorticoids – stimulate your bone marrow to release more neutrophils into your bloodstream. 
• Other medications like catecholamines and lithium, which are similar to glucocorticosteroids, may stimulate the mobilisation of neutrophils into the bloodstream.

Increased risk and prevention

While neutrophilia can affect anyone, certain factors may increase an individual's risk of developing this condition Some social factors increasing your risk are smoking, and stress. 

Additionally, studies have shown that neutrophil levels can vary among different ethnic groups. For example, individuals of African descent tend to have lower white blood cell counts, which might make them less likely to develop this condition. In contrast, those of Latino descent usually have higher neutrophil counts, which may increase their risk of neutrophilia.⁴

Some ways in which you can reduce your risk of developing this condition include:⁵

• Quit Smoking – smoking cessation can help lower neutrophil levels and reduce the risk of neutrophilia and other smoking-related health issues.
• Maintain a Healthy Lifestyle – adopting a balanced diet, regular exercise, and maintaining a healthy weight can support overall health and potentially reduce the risk of conditions that may lead to neutrophilia.
• Manage Stress – practising stress management techniques, such as meditation, yoga, or counselling, can help regulate the body's stress response and prevent stress-induced neutrophilia.
• Prevent Infections – taking preventive measures against seasonal infections, such as getting vaccinated against influenza, can reduce the risk of infections that may trigger neutrophilia.

Diagnosing neutrophilia

Because neutrophilia often occurs due to underlying health conditions, your doctor will do a physical examination first, looking for any signs of infection, inflammation, or blood disorders. Then, they will proceed to do a complete blood count (CBC) with differential, which is a blood test where they can count your white blood cells, and also the number of neutrophils. A peripheral blood smear may also be done, where the healthcare professional will manually look at a small blood sample under the microscope, looking at the shape of your neutrophils and other white blood cells. This often helps both diagnose and identify neutrophilia.

Once the neutrophilia is confirmed, there are additional tests your doctor might do to distinguish between primary and secondary neutrophilia. These include looking at markers of inflammation, tests to assess your liver and kidney function, and checking the ability of your blood to coagulate properly. Other tests that can be done to check for the possibility of malignancy include a bone marrow biopsy, as well as imaging techniques, such as computed tomography (CT), similar to X-rays, or magnetic resonance.¹ 

Common symptoms

Sometimes neutrophilia doesn’t have any symptoms. However, if your neutrophilia is causing a white blood cell count (leukocytosis), you may develop some symptoms, which include:^5,6

• Fever (temperature higher than 38°C or 100.4°F)
• Night sweats
• Unintended weight loss
• Fatigue
• Slow-healing sores or wounds
• Easy bruising

Managing neutrophilia and the importance of addressing the underlying cause

The management of neutrophilia primarily focuses on addressing the underlying cause, as neutrophilia itself is often a consequence of another condition. If the neutrophilia is caused by a previous infection or inflammation, your doctor may prescribe an antibiotic or anti-inflammatory therapy, to help your body clear the infection, reduce inflammation, and regain its balance. This will help lower your neutrophil numbers.

If certain medications are causing neutrophilia, your doctor may adjust the dosage or discontinue the medication if the side effects become problematic. In cases where neutrophilia is caused by blood cancers or myeloproliferative disorders, treatment may involve a range of drugs, such as cytoreductive agents like hydroxyurea, which work by decreasing the proliferation of neutrophils.¹  

Potential complications

Neutrophilia can sometimes lead to complications. Some of these include:¹  

• Impaired Wound Healing – excessive neutrophils can interfere with the body's ability to repair wounds and sores effectively.
• Increased Risk of Blood Clots – high neutrophil levels may contribute to an increased risk of developing blood clots (thrombosis).
• Increased Bleeding Risk – in some cases, neutrophilia can be associated with an increased risk of bleeding or bruising.

Because neutrophilia is a very complex condition, it often requires an interprofessional team of healthcare professionals, including haematologists, oncologists, and other specialists, to work together to diagnose and treat it. It is therefore very important to follow your doctor’s advice, monitor your neutrophil counts and symptoms, and take your medications to minimise the risk of any further complications.

FAQs

What is the difference between neutropenia and neutrophilia?

Neutropenia occurs when you have low levels of neutrophils, implying a weakened immune system and increased susceptibility to infections. In contrast, neutrophilia occurs when you have abnormally high levels of neutrophils in your blood. Although both can be due to bone marrow malignancies and adverse side effects of medications, they are distinct and can potentially be life-threatening if left untreated.⁷

Can neutrophilia be dangerous?

Neutrophilia itself may not be inherently dangerous, but it is essential to identify and treat the underlying cause. If left untreated, the underlying condition that led to neutrophilia can progress and potentially lead to serious complications, which may become life-threatening.

Can neutrophilia be chronic?

Yes, neutrophilia can be chronic if the underlying condition causing it persists over an extended period. Chronic neutrophilia often requires ongoing management and monitoring.

Summary

Neutrophilia is defined as an abnormally high level of neutrophils (white blood cells) in the blood, often occurring as a side effect of pre-existing underlying health issues. Normal neutrophil levels range from 2,500 to 7,000 per microliter, but factors like infections, stress, and certain medications can cause elevated counts. 

Although neutrophilia cannot be easily prevented as it can result from an infection, an arising blood disorder, or your genetics, preventive measures include lifestyle changes, such as quitting smoking and managing stress efficiently. Early diagnosis and monitoring are essential as complications may arise if left untreated, possibly becoming life-threatening in cases like cancer. Because neutrophilia is often a side effect of an underlying condition, it is imperative to address its root cause rather than the neutrophilia itself, whether this is a previous infection, persistent inflammation, side effects of medication, or a blood disorder.