What it is
The absolute neutrophil count is the number of mature neutrophils and bands per microlitre of blood — the single most important number for gauging a child’s risk of bacterial infection during chemotherapy, marrow failure, or congenital/cyclic neutropenia. The percentage differential alone is misleading; only the absolute count counts.
The formula
$$ ANC = WBC \times \frac{%,neutrophils + %,bands}{100} $$
WBC is in cells/µL (or ×10⁹/L). Include band forms (immature neutrophils) — omitting them underestimates the count. Do not include lymphocytes, monocytes, eosinophils, or basophils.
When to use it
Use it on every febrile oncology/transplant patient, before and during myelosuppressive therapy, and whenever neutropenia is suspected (sepsis, drug reaction, congenital syndromes). It drives isolation, antibiotic, and growth-factor decisions.
Worked example
WBC 2,000/µL, segmented neutrophils 30%, bands 5%:
$$ ANC = 2000 \times \frac{30 + 5}{100} = 2000 \times 0.35 = 700\ cells/µL $$
ANC 700 — severe neutropenia (CTCAE grade 3). With fever, this is febrile neutropenia and needs empiric antibiotics now.
CTCAE severity grades
- Grade 1 — ANC < LLN to ≥ 1,500/µL (mild)
- Grade 2 — 1,000 to < 1,500/µL
- Grade 3 — 500 to < 1,000/µL
- Grade 4 — < 500/µL (severe)
Risk of serious bacterial infection climbs steeply below 500/µL, and below 100/µL the host has almost no capacity to localise infection.
Febrile neutropenia is an emergency
Febrile neutropenia = ANC < 500/µL (or < 1,000 and predicted to fall below 500) plus a single temperature ≥ 38.3 °C, or ≥ 38.0 °C sustained > 1 hour. It is a medical emergency: blood cultures, then empiric broad-spectrum antibiotics within 60 minutes — do not wait for cultures, do not wait for the morning. The neutropenic host cannot mount the usual inflammatory signs, so a normal-looking child can be bacteraemic; subtle findings (mucositis, line-site tenderness, perianal pain) matter.
Pitfalls and caveats
- Always include bands — leaving them out can drop a child a whole grade.
- A rising trend can be falsely reassuring mid-nadir; correlate with the chemotherapy timeline (expected nadir ~7–14 days post-cycle).
- Absence of fever does not exclude sepsis in deep neutropenia or on steroids; treat strong clinical suspicion.
- Ethnic/benign neutropenia (e.g. constitutional) carries far lower infection risk than chemotherapy-induced counts at the same ANC — context matters.
- The number is a threshold for action, not a substitute for examining the child and reviewing the full count and film.
Run it: Absolute Neutrophil Count (ANC)
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.