Leukaemia Flow Cytometry in Yemen

Yemen is a country of approximately 35 million people in the Arabian Peninsula, with a median age of 19 years. It faces unique challenges due to the decade-long civil unrest, which has led to economic decline and resulted in one of the world's most devastating humanitarian crises. The relentless hostilities have devastated the lives of many through widespread food insecurity, recurring outbreaks of infectious disease, and deaths [1, 2]. This has been compounded by a scarcity of resources and a virtual collapse of the country's healthcare system. More than half of the medical facilities are only partially functioning or completely closed due to funding constraints and shortages of personnel, infrastructure, and medicine [1-3]. This health crisis has affected all aspects of public health and medical care, from diagnosis to patient management. Against this background of political instability, humanitarian plight, minimal resources, and economic crisis, health workers in Yemen are striving to deliver the best service possible for patients in need. This includes work in the field of haematology and providing pathology and clinical services to care for patients with blood cancers. Haematological malignancies, including leukaemia (5.7% of cancers; 4.2/100 000), are a significant and growing global health problem [1]. Here, we describe the creation of Yemen's first flow cytometry unit for leukaemia diagnosis amid war, systemic neglect, and scarcity of resources. It reflects the ethical, scientific, and human dimensions of practicing haematology within a collapsing health system. We show how this was achieved in this resource-constrained environment burdened by major geopolitical challenges. We illustrate the success of this programme through the analysis of 2 327 patients and show the value of outreach collaboration with international experts to ensure the service delivered was clinically useful and consistent with internationally accepted diagnostic approaches. Operating without institutional support or government funding, the development of flow cytometry relied on salvaged equipment, informal supply chains, and volunteer expertise. Key elements included the refurbishment of a second-hand single laser FACS Calibur flow cytometer (Becton Dickinson, San Jose, CA, USA), self-taught technical skills, and establishing reagent supply networks through returning patients and regional colleagues. Peripheral blood and bone marrow aspirate samples were received from healthcare facilities across Yemen. For local samples from Sana'a, analysis was typically completed within 24 h of collection. For samples transported from regional areas, delays related to distance, security conditions, and logistical constraints were common, but samples were generally analysed within 48 h. After red cell lysis, the samples were incubated with fluorophore-conjugated antibodies. Standardised panels were used for the immunophenotypic assessment, with marker selection guided by internationally accepted diagnostic approaches. Gating was based on CD45 expression and side-scatter characteristics. Following compensation and gating, a minimum of 10 000 events was acquired per sample. Samples were acquired on a BD FACS Calibur flow cytometer. Instrument calibration was performed using BD Calibrite beads in conjunction with BD FACS Comp software. Daily instrument optimisation and fluorescence compensation were carried out using normal peripheral blood stained with CD3, CD19, and CD45, analysed with BD CellQuest Pro software. Flow cytometry reports were issued within 48 h following sample receipt, except those that required discussion with international collaborators, which extended the turnaround time to up to 5 days. Despite these delays, clinically actionable results were consistently delivered within a timeframe that supported timely treatment decision-making. Over 6 years, samples from 2 327 paediatric (44%) and adult (56%) patients were analysed using antibody panels for the most common acute and chronic leukaemias (Table 1); these were jointly designed with international expert advice to meet diagnostic requirements. The panels, by necessity, were not standardised over the 6 years due to supply issues and resource limitations. There were variations in antibody clone and fluorophore, and in some situations, minimal diagnostic panels had to be used. Despite these limitations, leukaemias could be classified as acute (myeloid, B- and T-lymphoid) or chronic based on their morphology and immunophenotypic characteristics. Cases that were complex or did not fit the WHO diagnostic criteria were referred to the expert international panel (KAF, EC-S, and WNE) via email and/or online analysis of cytomorphology files using ‘GoToMeeting’ for diagnostic input. All patients (n = 2 327) Acute leukaemias predominate, consistent with patterns in developing countries. The proportion of lymphoblastic leukaemia was higher than in Western populations (e.g., SEER ~30% of all leukaemias). Paediatric patients (n = 1 024; 44%) ALL: 69% B-ALL: 80% T-ALL: 20% Adult patients (n = 1 303; 56%) Acute leukaemia: 70% Chronic leukaemia: 30% ALL: 47.3% B-ALL: 95% T-ALL: 5% CLL: 14.4% Hairy cell leukaemia: 1% AML less frequent than in Western cohorts (80%–85% of adult acute leukaemia), likely reflecting Yemen's younger population structure. Lower CLL burden than Western countries (14.4% vs. 25%–30%) may reflect demographic structure and/or underdiagnosis. The data demonstrates the significant burden of acute leukaemias, which comprised 83% of cases (54% lymphoid; 46% myeloid). In paediatric patients, 69% were lymphoid (80% B-cell lineage based on CD10, CD19, and CD22 expression) and 20% T-cell. In adults, AML was more common (52.7% of cases). This data aligns with global epidemiological trends, where acute leukaemias are more common than chronic forms, particularly in developing countries. Although much of the data showed similarities with other international settings, there were also differences. Of note was the higher proportion of acute leukaemias being lymphoblastic (54.1% of acute leukaemia cases) than typically reported in Western populations. For instance, the SEER database in the United States reports ALL comprising about 30% of all leukaemias in all age groups combined [4]. Possible explanations for these differences may be that adults with health problems are unable to attend hospitals due to the challenges posed by the civil unrest. It may also be due to the skewed demographics for Yemen, with 63% of the population under 25 years and less than 5% over 65 years (when chronic leukaemias are more prevalent) [5]. In children, the incidence of acute myeloid leukaemias (AML) was 31%, higher than in Western populations, and may also be due to environmental hazards or poor early life nutrition [6]. In adults, AML was less common (52.7% vs. 80%–85% of acute leukaemia); this may be due to the population makeup, as in Western countries, AML is most common in those over 65 years of age, but in Yemen, less than 5% of the population is in this age group [7, 8]. A total of 389 (17%) cases were chronic leukaemia, and these were all adult patients. However, the proportion of chronic lymphocytic leukaemia (CLL) among all leukaemias (14.4%) was lower than in Western countries, where CLL often accounts for 25%–30% of all leukaemias [9]. This discrepancy could also be due to differences in demographics or potential underdiagnosis of CLL in this setting. Analytical quality was achieved through the use of standardised antibody panels, consistent gating strategies, and daily instrument performance checks. Internal biological controls within each sample were used to verify antibody performance and fluorescence sensitivity. Expert interpretive oversight by international collaborators ensured consistency in data analysis and reporting. Participation in formal external quality assurance programmes was not feasible due to financial constraints, logistical barriers, and the security situation. Despite this limitation, the resulting immunophenotypic data were of clear clinical utility and aligned with internationally accepted diagnostic practice for leukaemia classification. Cancers are a growing burden on the Yemeni healthcare system, with leukaemia being one of the most common types [1, 10]. This is in part due to population growth at over 2% per annum, and the young median age of people in Yemen. Financial constraints and national security challenges impose huge obstacles in the delivery of health care. Here, we demonstrate that leukaemia immunophenotyping by flow cytometry can be successfully implemented in highly resource-constrained settings, even in the context of political instability, humanitarian crisis, and economic hardship, to assess leukaemias in patients of all ages. This experience illustrates that high-quality diagnostic haematology is achievable with limited infrastructure when supported by appropriate training, international collaboration, and targeted external support. However, our findings also highlight the inherent fragility of such services when they rely on a narrow workforce base and lack structural sustainability. In many low- and middle-income countries, advanced diagnostic laboratories are vulnerable to disruption due to insecurity, financial instability, workforce attrition, and limited institutional support. When these services fail, patients bear the consequences through delayed or inaccurate diagnosis and reduced access to optimal care. The loss of specialised diagnostic capacity described here reflects a broader challenge faced across the developing world: The difficulty of retaining skilled laboratory scientists in environments characterised by personal risk, inadequate remuneration, and limited career security. This represents not only a loss of individual expertise but also an erosion of local diagnostic capability that cannot be rapidly or easily replaced. These observations underscore the need for investment models that extend beyond equipment and reagents to include workforce protection, training succession, and long-term institutional support. Strengthening diagnostic haematology services in resource-limited settings will require sustained commitment from governments, international partners, industry, and philanthropic organisations. Without this, there will be an ongoing loss of expertise. Retention of trained, skilled personnel is essential to ensure diagnostic services remain accessible, regardless of geography or political context. All authors wrote and approved the submitted version of the manuscript. The flow cytometry testing was performed by S.A. K.A.F., E.C.-S., and W.N.E. provided collaborative expertise in data interpretation. The authors have nothing to report. The authors have nothing to report. The authors declare no conflicts of interest. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.