Low neutrophils means your blood has fewer infection-fighting white blood cells than normal, a condition called neutropenia. A normal neutrophil count falls between 1,500 and 8,000 cells per microliter of blood. When your count drops below 1,500, you’re considered neutropenic, and your body becomes less effective at fighting off bacteria and fungi.
What Neutrophils Do
Neutrophils are your immune system’s first responders. When bacteria or fungi enter your body, neutrophils rush to the site of infection faster than any other immune cell. They surround and swallow invading microorganisms, then destroy them using potent antimicrobial substances. They can even eject their own DNA to form web-like structures that trap and kill bacteria outside the cell.
This rapid defense buys your immune system time. Neutrophils hold infections in check during the hours and days it takes for slower, more specialized immune cells to mount a full response. Without enough neutrophils, even minor infections that your body would normally handle easily can become serious.
Mild, Moderate, and Severe Neutropenia
Not all low counts carry the same risk. Doctors classify neutropenia into three levels based on your absolute neutrophil count (ANC):
- Mild (1,000 to 1,500 cells/µL): Minimal infection risk. This often resolves on its own without any treatment.
- Moderate (500 to 1,000 cells/µL): Increased susceptibility to infections, particularly of the skin and the lining of your mouth and throat.
- Severe (below 500 cells/µL): Significantly higher risk of serious infections, including bloodstream infections, pneumonia, and painful mouth ulcers.
If your lab report shows a percentage rather than an absolute count, you can calculate your ANC by multiplying your total white blood cell count by the combined percentage of neutrophils (listed as “segs” and “bands” on your report), then dividing by 100.
Common Causes
Medications
Drugs are one of the most frequent causes of low neutrophils. Chemotherapy tops the list because it suppresses the bone marrow cells that produce neutrophils, and neutropenia is extremely common in cancer patients receiving these treatments. But many non-chemotherapy drugs can also lower your count. Antibiotics like amoxicillin, vancomycin, and trimethoprim-sulfamethoxazole are well-documented triggers. Antithyroid medications such as carbimazole and methimazole, the psychiatric drug clozapine, seizure medications like carbamazepine and phenytoin, and certain heart drugs including some ACE inhibitors and antiarrhythmics can all cause neutropenia.
In many of these cases, the drug triggers an immune reaction that destroys neutrophils in the bloodstream, or the drug’s breakdown products damage neutrophil-producing cells in the bone marrow. The neutropenia typically improves once the medication is stopped.
Infections
It sounds counterintuitive, but infections themselves can lower your neutrophil count. Viral infections are especially likely to do this. HIV, hepatitis, and tuberculosis are common infectious causes. Bacterial sepsis, where an infection spreads into the bloodstream, can also deplete neutrophils faster than the bone marrow can replace them. Even Lyme disease has been linked to temporary neutropenia.
Bone Marrow Problems
Since neutrophils are produced in the bone marrow, diseases that damage or crowd out normal marrow cells reduce neutrophil production directly. Aplastic anemia, in which the marrow stops making enough blood cells altogether, is one example. Leukemia and myelodysplastic syndromes, conditions where abnormal cells take over the marrow, also commonly cause neutropenia. Some people are born with genetic conditions that impair neutrophil production from early life.
Symptoms to Watch For
Neutropenia itself doesn’t cause symptoms you can feel. The danger shows up when infections take hold. Because your body has fewer defenders, infections can escalate quickly and produce fewer of the usual warning signs. You might not develop the redness or swelling you’d normally expect from an infected cut, for example, because those responses depend partly on neutrophils arriving at the site.
Fever is the most important signal. In someone with a very low neutrophil count, a fever of 100.4°F (38°C) or higher is treated as a medical emergency, a situation called febrile neutropenia. Other signs of infection to watch for include mouth sores, sore throat, skin infections that don’t heal, and chills or shaking.
How Low Neutrophils Are Treated
Treatment depends entirely on the cause and severity. Mild neutropenia with no symptoms often needs nothing more than monitoring with repeat blood tests. If a medication is responsible, switching to an alternative drug usually allows your count to recover.
For more serious cases, particularly chemotherapy-induced neutropenia, doctors can prescribe a growth factor that stimulates the bone marrow to produce neutrophils faster. This medication, approved by the FDA in 1991, works by signaling bone marrow cells to ramp up neutrophil production. Clinical trials have shown it can increase neutrophil counts tenfold, turning severe neutropenia into a mild or normal count. A longer-acting version is also available, requiring less frequent dosing. The treatment is given as an injection, typically under the skin, and continues until the neutrophil count climbs above 1,000 cells per microliter.
For people with severe aplastic anemia, adding this growth factor to standard treatment reduces infectious complications and time spent in the hospital. In congenital neutropenia, where people are born with persistently low counts, the goal of ongoing treatment is to keep neutrophils around 750 cells per microliter, enough to provide reasonable protection against infection.
Protecting Yourself With Low Neutrophils
If your neutrophil count is low, everyday infection prevention becomes critical. Handwashing is the single most effective measure. Wash thoroughly with soap and warm water before eating and after being in public spaces, and ask the people around you to do the same.
Avoid crowds and close contact with anyone who is sick or has recently received a live vaccine (such as for chickenpox or measles). Check your mouth daily for sores, which can be an early sign of infection. If you get a cut or scrape, clean it carefully and keep an eye on it.
Food safety matters more than usual when your neutrophil count is low. Cook meat, fish, and eggs thoroughly. Keep hot foods hot and cold foods cold. You may be advised to eat only fruits and vegetables that can be peeled, or to wash all raw produce very carefully. These steps reduce your exposure to bacteria that a healthy immune system would handle without trouble but that could cause real problems when neutrophils are scarce.