Absolute neutrophil count (ANC)

What is this for?

The absolute neutrophil count is the number of mature and immature neutrophils actually circulating, and it is the figure that determines infection risk. It gates chemotherapy administration, clozapine dispensing, and the definition of febrile neutropenia — none of which can be assessed from the total white cell count alone.

How to use it

1. Enter the white cell count exactly as the laboratory reports it — typically a number between about 1 and 20 representing thousands per mm³.
2. Enter the segmented neutrophil percentage from the differential.
3. Enter the band percentage. If the differential does not report bands, enter 0.

Worked example

A patient receiving chemotherapy has a WBC of 3.5 × 10³/mm³ with 40% segs and 5% bands. Calculate the ANC.

Answer: 3500 × (45 ÷ 100) = 1575 cells/mm³ — above the 1500 threshold, so not neutropenic.

Clinical pearls & pitfalls

• Bands must be included. Omitting them underestimates the ANC, and in a patient mounting a left shift the band count can be a substantial fraction of the total.
• A normal total white cell count does not exclude neutropenia. A WBC of 4.0 with only 15% neutrophils gives an ANC of 600 — severe neutropenia hidden behind a normal-looking number.
• Clozapine monitoring thresholds are defined by ANC, not WBC, under the current REMS programme. Benign ethnic neutropenia has separate, lower thresholds.
• Fever with an ANC below 500 is febrile neutropenia and requires empiric antibiotics within an hour. This is one of the few genuine pharmacy emergencies.
• Some differentials report "polys" or "PMNs" rather than segs — these are the same cells.

Assumptions & limitations

• Assumes the differential is accurate. Automated differentials may misclassify cells in the presence of blasts or dysplastic changes; a manual differential is more reliable in haematological disease.
• A point-in-time value. During chemotherapy the ANC is falling or rising rapidly, so the trend matters as much as the number.
• Does not assess neutrophil function, which can be impaired even when the count is normal — in diabetes, uraemia, or with corticosteroid use.

References

• Freifeld AG, et al. Clinical practice guideline for the use of antimicrobial agents in neutropenic patients with cancer: 2010 update by the IDSA. Clin Infect Dis. 2011;52(4):e56-e93.
• US Food and Drug Administration. Clozapine REMS Program — ANC monitoring requirements. link
• National Cancer Institute. Common Terminology Criteria for Adverse Events (CTCAE) version 5.0.

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