Neutrophils (Absolute) Blood Test

What Does This Test Measure?

Neutrophils are the most abundant white blood cells (50–70% of WBCs). They are the first line of defense against bacterial and fungal infections. Short-lived (hours to ~1 day), they respond rapidly to infection and inflammation.

Why Your Doctor Ordered This Test

The absolute neutrophil count is ordered as a component of the complete blood count (CBC) when a doctor suspects an acute bacterial or fungal infection, especially with fever, chills, or localizing signs like pneumonia or abscess. It’s essential for evaluating unexplained neutropenia or neutrophilia. In patients undergoing chemotherapy, serial ANC monitoring gauges the depth and duration of neutropenia to guide infection prophylaxis and the timing of the next cycle. Before starting medications known to cause agranulocytosis (such as clozapine, methimazole, or sulfasalazine) baseline and periodic ANC checks are mandated to detect precipitous drops. ANC is also ordered when a patient presents with sepsis or systemic inflammatory response syndrome (SIRS), as a rising ANC with immature “band” forms indicates an infection-driven demand on the bone marrow.

Doctors use the ANC to differentiate between viral infections, which typically leave the neutrophil count normal or slightly decreased, and bacterial infections, which classically elevate it. In the workup of recurrent infections, the ANC determines whether a quantitative neutrophil defect exists. Pre-surgical screening includes ANC to rule out occult risk of poor wound healing or post-operative infection. For patients with autoimmune diseases such as lupus or rheumatoid arthritis, ANC monitoring is necessary because the disease itself or its treatments (e.g., methotrexate) can cause neutropenia. Additionally, the test is used to diagnose benign ethnic neutropenia, a condition seen in individuals of African, Middle Eastern, or Mediterranean descent with persistently low but functional neutrophils, distinguishing it from pathological bone marrow failure.

What High Neutrophils Means

High neutrophils (neutrophilia): bacterial infection (most common), acute inflammation (surgery, trauma, burns, MI), corticosteroid effect (demargination), pregnancy, smoking, stress/exercise, and myeloproliferative neoplasms (CML). A "left shift" (immature band forms) distinguishes infection from steroid effect.

What Low Neutrophils Means

Low neutrophils (neutropenia): viral infections, chemotherapy/radiation, certain medications (clozapine, methimazole, sulfonamides), autoimmune conditions, bone marrow disorders, overwhelming sepsis, B12/folate deficiency, and benign ethnic neutropenia (ANC 1,000–1,500 in African/Middle Eastern/Mediterranean ancestry, benign).

How to Prepare and What Affects the Result

No fasting is required for a standalone absolute neutrophil count, but if it is part of a metabolic panel or glucose test, your doctor will ask you to fast for 8–12 hours. To avoid a falsely elevated result, you should not engage in strenuous exercise within 8 hours of the blood draw, because physical exertion temporarily demarginates neutrophils from vessel walls into the circulating pool, raising the count. Similarly, emotional stress and smoking can raise neutrophil numbers through catecholamine and cortisol release; it is best to avoid smoking for at least 30 minutes prior. Timing matters: neutrophil counts follow a diurnal rhythm with a trough in the morning and a peak in the afternoon, so when serial monitoring is needed, samples should be collected at the same time of day.

Many drugs profoundly alter the ANC. Glucocorticoids (prednisone, dexamethasone) cause redistribution neutrophilia, typically increasing counts by 2,000–4,000 cells/µL within hours. Lithium frequently elevates neutrophil levels, while colony-stimulating factors (G-CSF) are given therapeutically to boost counts. On the other hand, numerous medications can induce neutropenia or agranulocytosis, notably clozapine, methimazole, sulfamethoxazole-trimethoprim, and certain chemotherapeutic agents. If possible, discuss with your ordering clinician any prescription drugs, over-the-counter supplements (e.g., high-dose vitamin C or folic acid may confound interpretation), or herbal remedies. The blood sample is collected in an EDTA (lavender-top) tube, and must be processed within a few hours; delayed analysis can cause cell degradation and spuriously low counts.

Common Misinterpretations

One common misinterpretation is equating neutrophilia from corticosteroid use or physical stress with a bacterial infection. Glucocorticoids cause demargination, the detachment of neutrophils from the endothelial surface into the circulating pool, raising the ANC by 2,000–4,000 cells/µL in the absence of any actual infection or left shift. Failing to order a manual differential with band forms in a patient with a high ANC often leads to unnecessary antibiotics. Another error is overlooking benign ethnic neutropenia (BEN), a condition that affects 25–50% of individuals of African, Middle Eastern, and Mediterranean ancestry. These patients have an ANC between 1,000 and 1,500 cells/µL, yet their neutrophils function normally and they are not at increased infection risk. If clinicians are unaware, they may exhaustively work up the patient for bone marrow failure or discontinue essential drugs.

Confusing the absolute neutrophil count with the neutrophil percentage is a frequent mistake. A normal ANC can present with a low percentage in the setting of lymphocytosis, and conversely a low ANC can appear high-percentage when other cell lines are depressed. For example, after chemotherapy, the total WBC is very low, yet neutrophils may still constitute 80% of the count; leading to a false sense of security if the ANC is not calculated. Another misinterpretation arises when a sample is delayed in transport or stored at the wrong temperature, causing cell lysis and a pseudo-neutropenia. Repeating the collection with proper handling resolves this. Finally, transient neutropenia following a viral illness in children is often mistaken for a chronic condition, but counts typically recover within weeks; premature referral to hematology can be avoided by a repeat test after infection resolves.

Frequently Asked Questions

What does a high absolute neutrophil count indicate?

High ANC (>8,000 cells/µL), or neutrophilia, most often signals bacterial infection, especially when accompanied by immature band forms (left shift). Other causes include acute inflammation (surgery, trauma, burns, MI), corticosteroid use, pregnancy, smoking, and myeloproliferative disorders. A count of 15,000 with fever strongly suggests infection, while >25,000 may indicate a leukemoid reaction or chronic myeloid leukemia. Persistent unexplained neutrophilia warrants further investigation.

What causes low neutrophils (neutropenia)?

Low ANC (<1,500 cells/µL) results from viral infections (HIV, EBV, hepatitis), chemotherapy that suppresses bone marrow, or drugs like clozapine, methimazole, and sulfonamides. Autoimmune conditions, severe bacterial sepsis consuming neutrophils, and vitamin B12/folate deficiency also lower counts. Benign ethnic neutropenia (ANC 1,000–1,500) is harmless. An ANC below 500 dramatically raises infection risk; counts under 100 are a medical emergency.

Can stress or exercise raise my neutrophil count?

Yes. Intense physical exertion, acute emotional stress, or smoking rapidly demarginates neutrophils from vessel walls into the blood, often raising the ANC by 2,000–4,000 cells/µL within an hour. This effect is driven by catecholamine and cortisol release. Similarly, the pain or anxiety of the blood draw itself can cause a mild rise. To avoid a misleadingly high result, laboratories recommend avoiding strenuous exercise and smoking for 8 hours before the test.

What is a 'left shift' and why does it matter?

A left shift refers to the presence of immature neutrophil precursors (bands, metamyelocytes, and even myelocytes) in the peripheral blood. Normally, the bone marrow releases only mature segmented neutrophils. When the demand for neutrophils outpaces the marrow’s ability to mature them, as in severe bacterial infection or sepsis, younger forms appear. The degree of left shift helps distinguish true infection from corticosteroid-induced neutrophilia, which lacks shift. A pronounced left shift with toxic granulation is a strong indicator of acute bacterial sepsis.

How do steroids affect neutrophil levels?

Corticosteroids like prednisone raise the absolute neutrophil count through demargination, detaching neutrophils from the endothelial lining into the circulating pool, without increasing production. This causes a rapid rise of 2,000–4,000 cells/µL within hours of a dose. Steroid-induced neutrophilia lacks a left shift, helping to differentiate it from infection. Chronic use can also impair neutrophil function, so even with a normal or high ANC, patients may have increased infection risk.

Related Markers: Read Together for Full Context

BloodWorker reads lab values together, not in isolation. These related markers provide essential context for interpreting your Neutrophils result: