What brings you here today?
Choose the scenario that matches your patient. The panel below will update with the guidance you need.
1
Low neutrophil count on a routine FBC
Patient asymptomatic. FBC shows low neutrophils. Should you refer, repeat, or reassure?
2
Clozapine patient with amber or red blood result
Mental health patient on clozapine. CPMS flagged a low ANC. What do you do?
3
Explaining the result to the patient
Plain-language explainer you can read out, print, or paste into clinic notes.
Decision Tool — Routine Low Neutrophil Count
Answer the three questions below. The recommendation will appear at the bottom and update in real time.
1. Patient of African, Caribbean, Middle Eastern, Yemenite Jewish, or Ethiopian heritage?
DANC/ADAN is found in ~66% of US Black adults, ~90–100% of sub-Saharan African heritage, <1% European.
2. Is the ANC stable on historical FBCs? (no sustained downward trend)
Look back 6–24 months. Wide fluctuation around a stable mean is normal in DANC. A steady fall is not.
3. Any of: new symptoms (fevers, mouth ulcers, weight loss, night sweats), recurrent infections, or other low blood counts (anaemia, low platelets)?
Any of these red-flag features push the picture away from simple DANC.
Awaiting answers
Answer the three questions above
A recommendation will appear here once all three are selected.
📄 Ready-to-use templates
FBC including white cell differential.
Clinical details: [Patient ancestry, e.g. African heritage]. Stable mild-moderate neutropenia on previous FBCs. Asymptomatic. Investigating for Duffy-null associated neutrophil count (DANC). Please also process a Duffy phenotype (Fy a/b) if available through the transfusion lab — query DANC/ADAN.
Dear Haematology Team,
Re: [Patient name, DOB, NHS number]
I would be grateful for your review of this asymptomatic patient with persistent isolated neutropenia.
Background:
- Ethnicity: [African / Caribbean / Middle Eastern / Yemenite Jewish heritage]
- Current ANC: [x.xx × 10⁹/L]
- ANC trend on historical FBCs (last 6–24 months): [stable / falling / variable]
- Other lineages: [haemoglobin and platelet count]
- No constitutional symptoms, no recurrent infections
- Medications: [list]
- Spleen: [not palpable / palpable]
I have considered Duffy-null Associated Neutrophil Count (DANC / ACKR1-DARC-Associated Neutropenia, ADAN) as a likely cause given the patient's heritage.
Investigations requested:
- Duffy phenotype via local transfusion lab [if available]
- Haemoglobinopathy screen if clinically indicated and not previously done
I would value your specialist input on whether further investigation (including ACKR1 genotype, viral screen, B12/folate/copper, autoimmune screen, or bone marrow assessment) is indicated.
Yours sincerely,
Routine FBC showed ANC [x.xx × 10⁹/L]. This is below the standard reference range but consistent with Duffy-null Associated Neutrophil Count (DANC), a benign inherited variant common in people of African, Caribbean, Middle Eastern and Yemenite Jewish heritage. Trend stable on prior FBCs. Patient asymptomatic with no recurrent infections, no other cytopenias, no constitutional symptoms.
Plan:
- Explained DANC/ADAN to patient — benign, not immunodeficiency, no increased infection risk
- Duffy phenotype requested via transfusion lab
- Repeat FBC in [3-6 months] to confirm stability
- No haematology referral indicated at this stage
- Documented Duffy-null status on patient record to prevent unnecessary repeat workup or chemotherapy/clozapine dose-holds in future
Clozapine Patient with Amber / Red Blood Result
⚠ Do not stop clozapine alone in primary care
Clozapine withdrawal in a mental health crisis carries serious clinical risk. The decision to suspend, continue, or rechallenge sits with the patient's mental health team and haematology jointly. Your role in primary care is to coordinate, not decide.
- Confirm the result is real. Repeat FBC same day if practical, or arrange urgent pathology recheck. CPMS / ZTAS will already have flagged it.
- Check patient ancestry. If African, Caribbean, Middle Eastern or Yemenite Jewish heritage, consider DANC/ADAN as the likely cause of an apparent low ANC. UK pharmacogenomics guidance (CERSI-PGx 2026) now recommends ACKR1 genotype testing for clozapine patients with the Duffy-null phenotype.
- Contact the mental health team and haematology together. Do not wait. The team responsible for clozapine monitoring needs to know within the same working day. Phone, do not email.
- Send the patient to ED if: any sign of sepsis or the patient is unwell; ANC < 0.5 × 10⁹/L; or fever ≥ 38°C with ANC < 1.0 × 10⁹/L. If in doubt, treat as febrile neutropenia and refer.
- Document everything. Date, time, who you spoke to, decisions made, advice given to patient. Clozapine cases attract close governance review.
Background for context. Standard CPMS thresholds were derived from European populations with normal ACKR1 expression. Patients of African heritage with DANC may have a baseline ANC of 1.21–1.5 × 10⁹/L which sits within the Duffy-null reference interval but reads as "amber" on standard thresholds. The CERSI-PGx 2026 guideline recommends lowered thresholds for confirmed Duffy-null patients to prevent unnecessary clozapine suspension. This is a specialist decision — your job in primary care is to flag, not to override. Note: NICE and the British Society for Haematology have not yet issued DANC-specific clozapine monitoring thresholds. The CERSI-PGx guideline is a pharmacogenomics consortium consensus, not regulatory guidance.
Plain-English Patient Explainer
Read this out during the consultation, print it for the patient, or copy it into your notes. Written at approximately reading age 12.
Why is my white blood cell count lower than the normal range?
Your blood test shows that one type of white blood cell — called neutrophils — looks lower than the standard range printed on the report.
This is normal for many people of African, Caribbean, Middle Eastern, or Yemenite Jewish heritage. It is not a sign that your immune system is weak or that anything is wrong.
The reason is a small inherited difference in how your body stores its neutrophils. You make exactly the same total number as anyone else. The difference is that more of yours sit in your tissues, ready to act, while fewer sit in your bloodstream where the blood test measures them. The standard "normal range" on the report was worked out mostly from people of European heritage, where most of the neutrophils are in the blood. Your body keeps them somewhere else — but the same amount, doing the same job.
This has a name. Doctors used to call it "benign ethnic neutropenia". The more accurate name is Duffy-null associated neutrophil count (DANC), or ACKR1-DARC associated neutropenia (ADAN). The "Duffy" part refers to a blood group system, the same way A, B and O are blood groups.
What this means for you:
✓ You are not more likely to catch infections than anyone else.
✓ You do not need any treatment.
✓ You do not need a bone marrow test.
✓ Your immune system is working normally.
One thing worth doing: if you ever have chemotherapy, are started on a medication called clozapine, or need any treatment that affects the blood, please tell the doctor in charge that you have DANC/ADAN. Some treatments are paused if the blood count looks low — but if the doctor knows that a lower count is normal for you, they can keep the treatment going safely. It is worth asking your GP to record this clearly in your notes.
If you ever feel persistently unwell, develop a high fever, or notice you are getting infections more often than you used to, please come back to see your GP. That would not be DANC — it would be a reason for a fresh look.
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Decision-support, not decision-substitution. This page is a learning resource and clinical aid, calibrated against current UK guidance (CERSI-PGx 2026, BSH, Merz JAMA 2023). It does not replace clinical judgement, local referral pathways, or specialist input. For any patient where the picture is unclear or progressive, refer.
For colleagues who want the full clinical picture ↓
Duffy-null Lower Limit of Normal ANC
1.21 × 10⁹/L
vs Conventional Threshold
Duffy-null
1.21
Standard
1.50
Merz, JAMA 2023. ANC 1.21–1.5 × 10⁹/L in Duffy-null adults sits within the Duffy-null reference interval, not in the neutropenic range.
🔬 Click each cell to see the biology
Normal ANC ≥ 1.5
⟷
DANC ANC 1.21–1.5 ✓
ACKR1 receptor
Chemokine (CC/CXC)
Neutrophil
01 Terminology — What to Call It Now
Outdated
Benign Ethnic Neutropenia (BEN)
Historical label. Defines a non-White phenotype as disease against a White reference standard. Discouraged in current literature (Hibbs & Achebe 2023).
Descriptive
Duffy-null Associated Neutrophil Count (DANC)
Phenotype-anchored label. Dominant in haematology since 2021–2023. Used by ASH and most current trial protocols.
Preferred
ACKR1/DARC-Associated Neutropenia (ADAN)
Molecularly precise. Adopted by OMIM (611862) and UK CERSI-PGx 2026 clozapine guideline. Click to learn more.
02 Biology & Prevalence
Verified Molecular Biology
- Variant. Homozygous rs2814778 T>C in the ACKR1 promoter. Disrupts GATA-1 binding. Silences ACKR1/DARC on red cells; preserved on endothelium.
- Selection pressure. P. vivax resistance — the parasite uses ACKR1 to invade red cells.
- Mechanism. Altered neutrophil trafficking and chemokine handling. Total body neutrophil mass and marrow production are normal. (Proposed model — precise compartment biology under investigation; Liu & Luo 2024.)
- Host defence. Intact. Marrow reserve and stress release response preserved.
Population Prevalence (Homozygous ACKR1-null)
↑ Click any continent for detail
Very High (≥90%)
High (50–80%)
Moderate (~66%)
Low (<1%)
🧮 Interactive ANC Interpreter — Move the slider, then toggle Duffy-null to see the difference
1.35
✓ ANC 1.35 × 10⁹/L — WITHIN THE DUFFY-NULL REFERENCE INTERVAL (≥ 1.21). No action required. Document DANC on EPR.
03 Diagnostic Algorithm — Adult
1
Confirm Stable, Isolated
Historical FBCs. No other cytopenia. No constitutional symptoms. No severe infection history.
2
Exclude Acquired Causes
HIV, hepatitis B/C, EBV. B12, folate, copper. Autoimmune screen. Drug history. Spleen size.
3
Test Duffy Status
Fy(a–b–) phenotype on serology, OR homozygous ACKR1 rs2814778 C/C genotype.
✓
No Bone Marrow Biopsy
Confirmed DANC → BMB not indicated. Document on EPR. Reserve for new fall, additional cytopenia, or abnormal film.
04 Management Pathways
💊
Clozapine (UK)
CERSI-PGx 2026
CERSI-PGx 2026
- Pre-emptive ACKR1 genotype at initiation
- Reactive testing after amber/red result or CNRD
- Confirmed Duffy-null → revised lower thresholds
- Haematology if WBC < 2.0 or ANC < 1.0 + fever ≥ 38°C
🧬
Oncology & Chemotherapy
- No pause/dose-reduction for ANC 1.21–1.5 in Duffy-null
- Standard febrile neutropenia protocol for marrow suppression
- G-CSF not indicated for DANC alone
- 76.5% of phase 3 trials exclude DANC-range ANCs (Hibbs 2024)
🩸
General Haematology
- Confirmed DANC only → discharge to GP with explanation
- Unconfirmed Duffy + relevant ancestry → test first
- Biopsy only for new fall, additional cytopenia, features
- Document Duffy-null on EPR — prevents repeat workups
05 Fluctuating Counts — A Verified Pattern, Not a Red Flag
Many Duffy-null patients show a wide ANC range across serial counts, sometimes dipping into the severe range (0–0.5 × 10⁹/L) and rising into the normal range during infection, pregnancy or physical stress. This is the documented behaviour of DANC/ADAN itself — not evidence of a separate pathology. The total body neutrophil mass and marrow reserve are normal; the circulating compartment is small but fully responsive to stress demargination.
Paediatric ADAN
59%
had ANC in severe range (0–0.5 × 10⁹/L) at diagnosis
Oz-Alcalay 2024, n=49
During fever
72%
had ANC rise into normal range during febrile illness
Oz-Alcalay 2024, n=47
Adult range
0.74–1.80
IQR of ANC in confirmed Duffy-null adults (× 10⁹/L)
Zammar 2025, n=10
↕ FLUCTUATION (reassuring) vs ↓ PROGRESSIVE FALL (investigate)
Wide irregular variability around a stable mean, with nadirs sometimes in the severe range and peaks reaching normal — particularly during infection or stress. This is DANC behaving normally. No additional workup is needed once Duffy-null status is confirmed.
Steady downward trend over months, new cytopenia in another lineage, constitutional symptoms, or recurrent infections at the nadirs. This warrants investigation regardless of Duffy status — DANC and acquired neutropenia can coexist.
⚠ Common Pitfalls — What to Avoid
Confusing fluctuation with progression — DANC can vary widely between counts. Look for a sustained downward trend or new lineage cytopenia, not single low values.
Applying 1.5 × 10⁹/L cut-off to confirmed Duffy-null — pauses chemo or clozapine unnecessarily.
Quoting "80–100% of African ancestry" as prevalence. Verified figure: ~66% in US Black adults.
Using "benign ethnic neutropenia" in clinical letters. Replace with DANC or ADAN.
Repeating bone marrow biopsy because Duffy status was never documented on the EPR.
"Neutrophils rest in tissues" is an oversimplification. Mechanism is altered trafficking, not dormancy.