A low absolute neutrophil count (ANC) means your body has fewer infection-fighting white blood cells than normal. A healthy ANC typically falls between 1,500 and 7,000 cells per microliter of blood. When your count drops below 1,500, the condition is called neutropenia, and it signals that your immune system’s front line of defense is weakened.
This result shows up on a standard blood test called a complete blood count, or CBC. It can be caused by something as temporary as a viral infection or as significant as a bone marrow disorder. How much it matters depends largely on how low the number is and what’s driving it down.
What Neutrophils Actually Do
Neutrophils are the most abundant type of white blood cell and arguably the most effective bacteria killers in your body. They’re part of your innate immune system, meaning they respond immediately to threats rather than needing time to “learn” a pathogen the way other immune cells do. When bacteria enter through a cut or reach your lungs, neutrophils are the first responders that arrive to engulf and destroy the invaders.
This is why a low count matters practically: with fewer neutrophils patrolling your bloodstream, infections that your body would normally handle without you ever noticing can gain a foothold and become serious.
How Low Is Too Low
Neutropenia is classified by severity based on your ANC:
- Mild neutropenia: 1,000 to 1,500 cells per microliter. Your infection risk is only slightly elevated.
- Moderate neutropenia: 500 to 1,000. Infections become a more meaningful concern.
- Severe neutropenia: below 500. Your body has very limited ability to fight off bacteria.
- Profound neutropenia: below 100. Even minor exposures to bacteria can lead to life-threatening infections.
If your count is mildly low, say around 1,200 or 1,300, that’s a very different clinical picture than a count of 300. Context matters too. A single low reading after a cold may not concern your doctor much, while a persistently low count with no obvious explanation will prompt further investigation.
Common Reasons Your Count May Be Low
Viral Infections
One of the most frequent causes is a recent or active viral infection. Chickenpox, COVID-19, hepatitis A through C, HIV, measles, Epstein-Barr virus, and cytomegalovirus can all temporarily suppress neutrophil production or pull them out of the bloodstream faster than your bone marrow replaces them. In many of these cases, the count recovers on its own once the infection clears.
Medications
A wide range of prescription drugs can lower your ANC, and this is one of the first things doctors check. Chemotherapy drugs are the most well-known cause because they broadly suppress the bone marrow, where neutrophils are made. But many non-chemotherapy drugs can do it too. Common culprits include certain antibiotics, medications for overactive thyroid, anti-inflammatory drugs used for rheumatoid arthritis or ulcerative colitis, certain antipsychotic medications, heart rhythm drugs, and some acne treatments. If you recently started or changed a medication, that’s worth mentioning to your doctor.
Autoimmune Conditions
In autoimmune neutropenia, your immune system mistakenly targets and destroys your own neutrophils. Lupus and rheumatoid arthritis are among the autoimmune conditions associated with this. Sometimes the neutropenia is actually the first sign that an autoimmune process is happening.
Bone Marrow Problems
Because neutrophils are produced in the bone marrow, conditions that damage or crowd out normal marrow function can cause low counts. These include leukemia, aplastic anemia (where the marrow stops producing enough blood cells), and myelodysplastic syndromes (where the marrow produces abnormal cells). Severe bacterial infections like sepsis can also overwhelm the marrow’s ability to keep up with demand, temporarily depleting neutrophils.
Some people have a chronically low ANC without any disease at all. This is particularly common in people of African and Middle Eastern descent, where a baseline ANC below 1,500 can be completely normal. This is sometimes called benign ethnic neutropenia and doesn’t increase infection risk.
Signs That Low Neutrophils Are Causing Problems
Neutropenia itself doesn’t produce symptoms you can feel. You won’t know your count is low unless blood work reveals it. What you will notice are the infections that take hold because of it. Watch for:
- Fever above 100.4°F (38°C): This is the single most important warning sign, especially if you know your ANC is low.
- Mouth sores or a sore throat that develops without an obvious cause.
- Skin infections: redness, swelling, or warmth around cuts or wounds that aren’t healing normally.
- Chills and sweats, a worsening cough, or shortness of breath.
- Burning or pain during urination, diarrhea, or new abdominal pain.
Fever combined with severe neutropenia is considered an emergency, particularly for people undergoing cancer treatment. This combination, called febrile neutropenia, requires immediate antibiotic treatment because infections can escalate dangerously fast when your neutrophil count is very low.
How Doctors Investigate a Low Count
The first step is usually looking at your previous blood counts to see whether this is new or longstanding. A single mildly low result, especially during or just after an illness, often just needs a recheck in a few weeks. Your doctor may order blood counts several times a week for six to eight weeks to track the trend.
If the low count persists after stopping any suspect medications and ruling out infections, a bone marrow biopsy becomes the next step. This is considered necessary for anyone whose neutropenia doesn’t resolve or who has multiple types of blood cells affected (not just neutrophils). The bone marrow sample can be analyzed for signs of leukemia, myelodysplastic syndromes, or infections like tuberculosis and fungal diseases that might be suppressing production.
Additional blood tests may check for autoimmune antibodies, vitamin deficiencies like B12 or folate, and viral infections that haven’t been identified yet.
How Low Neutrophils Are Treated
Treatment depends entirely on the cause and severity. If a medication is responsible, stopping or switching that drug often allows neutrophil counts to recover within days to weeks. If a viral infection is the trigger, the count typically rebounds as the infection resolves.
For people with severe or chronic neutropenia, a medication that stimulates the bone marrow to produce more neutrophils may be prescribed. This drug, a growth factor called G-CSF, is FDA-approved for both inherited and acquired forms of neutropenia. It’s most commonly used during cancer treatment, where guidelines recommend it when the risk of febrile neutropenia exceeds 20%. It’s also used for people born with congenital neutropenia or those with cyclic neutropenia, where counts dip dangerously low in a recurring pattern every few weeks.
For autoimmune neutropenia, treatment may involve medications that quiet the immune system’s attack on neutrophils. In many mild cases, no treatment is needed at all. Your doctor may simply monitor your counts periodically and focus on managing infections quickly if they arise.
Living With a Low Neutrophil Count
If your ANC is chronically or temporarily low, the practical goal is reducing your exposure to infections. This means being attentive to hand washing, avoiding people who are actively sick, and keeping cuts and scrapes clean. Dental hygiene matters more than usual because the mouth is a common entry point for bacteria.
Knowing your baseline number helps you and your doctor gauge risk. If your ANC is 1,200 and stable with no history of unusual infections, you’re in a very different situation than someone at 400 who’s getting recurrent fevers. The number on your lab report is a starting point for a conversation, not a diagnosis by itself.