Background Laboratory reference intervals must reflect population diversity for accurate medical decisions. The Duffy null variant lowers absolute neutrophil counts (ANC), but existing dedicated reference intervals are based on a single African American cohort. The impact across other ethnic groups and regions remains unclear, and no white blood cell count (WBC) intervals exist for Duffy null individuals. This study aimed to establish and compare Duffy null ANC and WBC reference intervals across four continents.

Methods A cross-sectional study was conducted assessing healthy Duffy null individuals from dedicated cohorts (blood donors in Namibia and Saudi Arabia, and primary care patients in the USA) and biobanks (participants from the UK and USA). Reference intervals were determined using Clinical & Laboratory Standards Institute guidelines.

Results Among 7,872 participants (392 from dedicated cohorts, 7,480 from biobanks), novel ANC and WBC reference intervals were established: Namibia (820–6,370/μL; 2.51–9.85× 109/L), Saudi Arabia (1,090–5,100/μL; 3.71–9.95× 109/L), and the USA (1,210–5,390/μL; 3.00-9.66× 109/L), with no significant differences between cohorts. Institutional reference intervals misclassified 27.9% (Namibia), 50.7% (Saudi Arabia), and 21.7% (USA) as neutropenic. Biobank analyses confirmed a significantly lower ANC in Duffy null individuals compared to Duffy non-null (p<0.0001) with no significant difference in ANC between Black and non-Black Duffy null participants.

Conclusions Duffy null individuals consistently exhibit lower ANC and WBC across ethnic groups and regions. Current reference intervals overlook this variation, risking misdiagnosis and health inequities. Implementing Duffy-specific reference intervals is essential for equitable and accurate clinical decisions worldwide.

Key points

– Novel ANC and WBC reference intervals for Duffy null adults were established and are consistent across four continents

– Current ANC reference intervals misclassify up to half of Duffy null individuals as neutropenic, contributing to global heath inequities.

Stephen P Hibbs, Israel Chipare, Amr J Halawani, Sophie E Legge, Geoffrey Fell, Daniel Dees, Abdulrahman A Alhamzi, Edwig Shingenge, Mohammed J Alabdly, Hilary T Charuma, Mohammed A Nushaily, Judith M Sinvula, Menelik Russo, Michelle Sholzberg, and Nancy Berliner report no conflicts of interest. Sara Paparini has received funding for research from ViiV Healthcare and Gilead Science for studies unrelated to this manuscript. Vanessa Apea has received speaker fees from ViiV, Gilead and MSD. Maureen Okam Achebe is on the advisory committee for Global Blood Therapeutics, Pharmacosmos, Vertex Pharmaceuticals, and Fulcrum. Lauren Merz has consulted for J&J.

Stephen P. Hibbs is supported by a HARP doctoral research fellowship, funded by the Wellcome Trust (Grant number 223500/Z/21/Z); Sophie Legge is supported by the Medical Research Council; and Lauren E. Merz is supported by a Brigham and Womens Hospital Health Equity and Innovation Pilot grant.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

For Namibia: Ethical approval was obtained from the Ministry of Health and Social Services, Namibia University of Science and Technology Ethical Committee, and the Blood Transfusion Service of Namibia. For Saudi Arabia: Ethical approval was obtained from the Jazan Health Ethics Committee. For Boston (USA): Brigham and Women's Hospital Institutional Review Board approval (2020P001517)

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