Has a blood test ever flagged your neutrophils or white blood cells as low, even though you felt perfectly healthy? For millions of people in the US, the explanation is a harmless inherited trait called Duffy null. On 5 November 2026, the American Society of Hematology (ASH) journal Blood Advances published the first Duffy-null reference ranges for children, along with a large check of the adult ranges. Here is what the study found, what it means for reading your complete blood count (CBC), and which questions to ask your doctor.
What does Duffy null mean?
Duffy is a blood group system, like ABO or Rh, though far less familiar. It refers to a protein found on the surface of red blood cells. In people who are Duffy null, written Fy(a-b-), a small change in the ACKR1 gene keeps that protein off the red cells. The variant is very common in people with African ancestry, and it protects against one type of malaria. The researchers estimate that about 10% of the US population is Duffy null.
The trait's most visible effect in the lab is a lower count of neutrophils circulating in the blood, without more infections. A large genetic study across three US biobanks, including All of Us and the Million Veteran Program, found that Duffy-null status was consistently linked only to lower white blood cell counts, not to any disease. Experts now call this pattern Duffy null-associated neutrophil count, or DANC, instead of the older term "benign ethnic neutropenia."
What the new study found
Researchers at 23 US sites, led by haematologist Lauren Merz and colleagues, enrolled 1,412 healthy people with confirmed Duffy-null status, from 6 months of age to adulthood. Using standard laboratory guidelines, they calculated the ranges where these people's absolute neutrophil count (ANC) and white blood cell count (WBC) normally fall.
| Age group | ANC (×10⁹/L) | WBC (×10⁹/L) |
|---|---|---|
| 6 months to 2 years | 0.53 to 4.50 | 4.4 to 12.6 |
| 3 to 6 years | 0.78 to 4.67 | 3.8 to 10.8 |
| 7 to 12 years | 0.87 to 5.34 | 2.9 to 10.1 |
| 13 to 17 years | 0.90 to 4.89 | 3.1 to 9.2 |
| Adults (18 and older) | 1.03 to 7.30 | 3.0 to 10.7 |
Ranges proposed by Merz and colleagues (Blood Advances, 2026) for healthy Duffy-null people. On many US lab reports, 1.03 ×10⁹/L appears as 1,030 cells per microliter or 1.03 K/µL. These ranges do not replace your lab's own ranges and do not apply to people who are not Duffy null.
Key takeaways:
- One in four healthy Duffy-null adults had an ANC below 2.0, and between a quarter and half of the children, depending on age, were below 1.5, the usual cutoff for neutropenia.
- Results held regardless of the blood analyser, clinic setting, or how the sample was drawn.
- These are the first published Duffy-null ranges for children; data for babies under 6 months are not yet available.
A companion paper from the same group lays out a roadmap for hospitals and labs: test for Duffy status, record it in the health record, update lab software, and educate clinicians and patients.
Why it matters: fewer unnecessary tests
When standard ranges are used, a healthy Duffy-null person can be labelled neutropenic. According to ASH and the published research, that mislabel can lead to repeat testing, referrals, and even bone marrow biopsies, along with delayed or reduced treatments and exclusion from clinical trials. One analysis of phase 3 trials for the five most common cancers in the US and UK found that about three in four excluded patients whose ANC was normal for a Duffy-null person, and that more than half of standard cancer drug regimens called for dose changes at those levels.
The issue is not limited to the US. A 2026 study in Blood with participants from Namibia, Saudi Arabia, the UK, and the US found very similar Duffy-null ranges across countries. Local lab ranges wrongly classified roughly a quarter to half of these healthy people as neutropenic, and among Duffy-null participants, race did not change the results. In other words, the blood group drives the lower count, not race itself, which is why experts recommend testing rather than guessing.
What the study does not say
- A low count is not always due to Duffy null. A new or very low ANC, or one that comes with infections, mouth sores, anaemia, or low platelets, still needs a full work-up.
- Ancestry alone cannot confirm the trait; only a Duffy blood test can.
- The ranges describe healthy people. They do not set the thresholds your oncology team uses during chemotherapy.
Recent advances
Research on this topic has moved fast in three years. In 2023, a primary care study found that two in three Black adults tested were Duffy null and had clearly lower neutrophil counts, and its authors called for dedicated ranges. In 2024, researchers showed how often cancer trials excluded these patients. In 2025, a large genetic study confirmed that the trait carries no disease risk and is also found in people with Middle Eastern, Hispanic, or mixed ancestry. In 2026, a multinational study and the two new Blood Advances papers delivered adult and, for the first time, paediatric ranges. What it means for you: a slightly low, stable neutrophil count with no symptoms may be completely normal if you are Duffy null, and a simple blood test can tell you whether you are.
Which tests can monitor or screen for this?
- Complete blood count (CBC) with differential: counts white blood cells, neutrophils, red blood cells, and platelets. A low neutrophil count with normal red cells and platelets is the typical DANC pattern.
- Repeat CBCs over time: a count that stays stable for months, without symptoms, is reassuring.
- Duffy red blood cell phenotyping: a blood test that looks for the Fy(a) and Fy(b) antigens, already used in blood banks. When both are absent, you are Duffy null. A genetic test for the rs2814778 variant is another option.
- Further tests your doctor may order if the picture is not typical: medication review, viral tests, autoimmune markers, or a haematology referral.
To learn more about other causes, see our guide to low absolute neutrophils and our overview of the white blood cell count.
When to see a doctor
- Right away, or call 999, if you have a fever and a known low neutrophil count, especially during cancer treatment.
- Promptly if the drop is new or very low (below 0.5 ×10⁹/L), or comes with anaemia or low platelets.
- If you have frequent infections, recurring mouth sores, or bleeding gums.
- If several blood tests have shown low neutrophils: ask whether Duffy testing makes sense and whether the result can be recorded in your medical record.
Glossary
- Neutrophils: the most common white blood cells, the body's first line of defense against bacteria.
- Absolute neutrophil count (ANC): the number of neutrophils in a given volume of blood.
- Neutropenia: an ANC below the lab's lower limit, usually 1.5 ×10⁹/L in adults.
- Duffy null, Fy(a-b-): absence of the Duffy antigen on red blood cells, a harmless inherited trait.
- DANC: Duffy null-associated neutrophil count, the current name for the trait's lower but healthy counts.
- Reference range: the interval that contains the results of 95% of healthy people in a given population.
- Phenotyping: a lab test that identifies which blood group antigens are present on red blood cells.
Frequently asked questions
Is Duffy null-associated neutrophil count dangerous?
No. Research shows it does not raise the risk of infection or any disease. It matters only because it can be mistaken for true neutropenia and lead to unnecessary tests.
How do I find out if I am Duffy null?
Through a blood test that checks for the Duffy antigens on your red cells, or a genetic test. Your doctor may order it if your neutrophils are repeatedly low with no other explanation.
Will my lab report start using the new ranges?
Not automatically. Each lab sets its own ranges, and adopting Duffy-null ranges requires knowing your Duffy status. ASH and the study authors are encouraging hospitals and labs to make that change.
My child has low neutrophils. Is it Duffy null?
Not necessarily. In children, viral infections often cause a temporary drop. A repeat test and, if needed, a specialist opinion can tell the difference.
Does Duffy status matter for chemotherapy?
It can, because many regimens adjust doses based on neutrophil counts. Tell your oncology team your Duffy status; they decide which thresholds apply.
Sources
- Merz LE, Fink A, Han H, Jacquot C, et al. Establishing absolute neutrophil count and white blood cell count reference intervals for the Duffy null population. Blood Advances, 2026. DOI: 10.1182/bloodadvances.2026020900
- Merz LE, Chang VY, Fingrut WB, Godley LA, et al. A roadmap for developing and implementing Duffy null-specific reference intervals. Blood Advances, 2026. DOI: 10.1182/bloodadvances.2026021681
- Hibbs SP, Chipare I, Halawani AJ, Legge SE, et al. Multinational assessment of absolute neutrophil counts and white blood cell counts among healthy Duffy-null adults. Blood, 2026. DOI: 10.1182/blood.2025029359
- Hysong MR, Shuey MM, Huffman JE, Auer P, et al. Characterization of the phenotypic consequences of the Duffy-null genotype. Blood Advances, 2025. DOI: 10.1182/bloodadvances.2024014399
- Hibbs SP, Aiken L, Vora K, Mowete C, et al. Cancer trial eligibility and therapy modifications for individuals with Duffy null-associated neutrophil count. JAMA Network Open, 2024. DOI: 10.1001/jamanetworkopen.2024.32475
- Merz LE, Story CM, Osei MA, Jolley K, et al. Absolute neutrophil count by Duffy status among healthy Black and African American adults. Blood Advances, 2023. DOI: 10.1182/bloodadvances.2022007679
- Merz LE, et al. Development of Duffy null-specific absolute neutrophil count reference ranges. JAMA, 2023. DOI: 10.1001/jama.2023.7467
- Medical Xpress (American Society of Hematology). New blood count ranges could prevent unnecessary testing for people with Duffy-null trait, 5 November 2026
Other articles
- Low absolute neutrophils: causes, symptoms, and treatment
- Neutrophils explained: making sense of your blood work
- White blood cell count: what your results mean
- Complete blood count (CBC): a full guide
- CBC vs. CMP: understanding the tests
- High neutrophils: causes, symptoms, and risks
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