Utility of Iron Staining in Bone Marrow Aspirates in the Era of Next-Generation Sequencing: A Retrospective Single-Centre Study.

Abstract

Introduction: Bone marrow iron staining is traditionally used to assess iron stores and identify ring sideroblasts (RS), a key feature of sideroblastic anaemia and historically important in the classification of myelodysplastic and myelodysplastic/myeloproliferative overlap neoplasms. With the adoption of the WHO 2022 classification and increasing availability of next-generation sequencing (NGS), the diagnostic relevance of routine iron staining warrants re-evaluation.

Methods: We retrospectively analysed 101 consecutive adult diagnostic bone marrow examinations (51 myeloid, 50 lymphoid) performed at a regional Australian hospital between January 2023 and June 2024. Perls' Prussian blue staining was routinely performed. Ferritin was available in 76% of cases, and molecular testing in 35% of cases. Two independent reviewers graded bone marrow iron using the Gale score and enumerated RS. Diagnostic impact was categorised as either no impact, supportive but non-essential, or potential diagnostic miss. Interobserver agreement, correlation with serum ferritin, and diagnostic performance for iron deficiency were evaluated.

Results: Iron staining had no diagnostic impact in 94% of cases and was supportive but non-essential in 6%; omission would not have altered the final diagnosis in any case. RS ≥ 15% were identified in seven myeloid cases, including MDS, AML, and therapy-related myeloid neoplasms. SF3B1 mutations were present in three RS-positive cases; RS presence did not independently determine diagnosis. Interobserver agreement for iron grading was good (weighted κ = 0.77, 95% CI 0.64-0.89). Correlation between marrow iron grade and serum ferritin was weak (r ≈ 0.38). Low marrow iron grade (≤ 1) showed variable sensitivity (33% to 67%) but high specificity (> 90%) for iron deficiency.

Conclusion: Routine bone marrow iron staining rarely influences diagnostic classification in contemporary practice. RS morphology is supportive but not determinative, and marrow iron grading correlates poorly with systemic iron status. These data support a targeted rather than routine approach to marrow iron staining, particularly where NGS is available and routinely performed in de novo diagnoses.