Diagnostic Utility and Sensitivity of Red Cell Distribution Width (RDW) and Peripheral Blood Smear Morphology in the Early Detection and Severity Grading of Iron Deficiency Anemia: A Cross-Sectional Analytical Study

Abstract

Anemia is a major global public health challenge characterized by a reduction in circulating red blood cell (RBC) mass, hemoglobin (Hb) concentration, or packed cell volume (hematocrit), resulting in impaired tissue oxygenation. Iron deficiency anemia (IDA) accounts for the vast majority of microcytic hypochromic anemias worldwide, affecting approximately 800 million women and children and contributing substantially to morbidity and disability-adjusted life years in low- and middle-income nations. While definitive biochemical confirmation via bone marrow iron staining or serum ferritin radioimmunoassay remains costly, invasive, or unavailable in routine primary and secondary healthcare setups, automated Red Cell Distribution Width (RDW) provides an immediate, quantitative index of erythrocyte volume heterogeneity (anisocytosis). To evaluate the diagnostic utility, clinical sensitivity, and morphological concordance of automated Red Cell Distribution Width (RDW) and Giemsa-stained peripheral blood film (PBF) examination in the early detection and severity grading of iron deficiency anemia, and to correlate RDW alterations with conventional Wintrobe RBC indices. A cross-sectional comparative analytical study was conducted at the Hematology Laboratory of Wazir Hospital, Township, Lahore, Pakistan, in collaboration with the Department of Medical Laboratory Technology, Minhaj University Lahore, over a six-month period from January 2021 to July 2021. Using non-probability purposive sampling, a total of 504 adult anemic patients (Hb < 11.0 g/dL) aged 25 to 70 years presenting with predominant microcytosis (MCV < 80 fL) were enrolled. Patients on active iron supplementation or with recent blood transfusions were excluded. Venous blood specimens (3 mL in K3-EDTA vacutainers) were analyzed on a 20-parameter automated hematology analyzer (Medonic M-Series M32, Boule Medical AB, Sweden) for Hb, total RBC count, HCT, MCV, MCH, MCHC, RDW-CV, and RDW-SD. Blinded senior hematopathologists evaluated Giemsa-stained peripheral blood smears under 100x oil immersion microscopy. Among the 504 enrolled cases, 368 (72.0%) were females, 136 (27.0%) were males, and ~1.0% represented borderline pediatric/adolescent referrals, with 80.0% of cases clustered in the reproductive and economically active age group of 25–50 years. Cutaneous and mucosal pallor was the predominant clinical manifestation (70.0%). Stratification by anemia severity revealed mild anemia (Hb 10.0–11.0 g/dL) in 10.0% (n = 50), moderate anemia (Hb 7.0–9.9 g/dL) in 80.0% (n = 404), and severe anemia (Hb < 7.0 g/dL) in 10.0% (n = 50) of the cohort. Overall, RDW was abnormally elevated (> 14.5%) in 75.0% of the total study population. Notably, in moderate and severe IDA grades, 100.0% of progressive microcytic cases demonstrated elevated RDW, whereas in mild (early-stage) IDA, 75.0% to 80.0% of patients already exhibited abnormal RDW elevation prior to uniform reductions in MCHC (which remained normal in 61.0%–65.0% of patients). Peripheral blood smears corroborated microcytic hypochromic morphology with marked anisopoikilocytosis. Red Cell Distribution Width (RDW) is a highly sensitive, rapid, and cost-effective frontline screening biomarker for the early identification of iron deficiency anemia. Combining an automated threshold of RDW > 15.0% with Hb <= 10.0 g/dL and targeted peripheral smear review enables reliable detection of IDA in high-volume, resource-constrained hospital laboratories, substantially reducing diagnostic turnaround time and unnecessary biochemical expenditure.