Diagnostic Utility of Complete Blood Count Indices in Ferritin‐Defined Microcytosis Among United States Women Aged 18–49 Years
Jinxiao Hou, Xiaodong Shang, Hengwei Zhang, Dachuan FanABSTRACT
Introduction
Complete blood count (CBC) discrimination indices are widely used as low‐cost triage tools for microcytosis, but their diagnostic utility in population‐based samples with ferritin‐defined iron status is uncertain. We evaluated whether commonly used indices distinguish ferritin‐defined iron‐deficient from noniron‐deficient microcytosis among women aged 18–49 years.
Methods
We analyzed the National Health and Nutrition Examination Survey (NHANES) 2015–2016, 2017–2018, and August 2021–August 2023 data among nonpregnant women aged 18–49 years with CBC, serum ferritin, and survey design variables. Among microcytic (MCV < 80 fL) women, iron‐deficient microcytosis was defined as ferritin < 15 ng/mL and noniron‐deficient microcytosis as ferritin ≥ 15 ng/mL. Mentzer, England–Fraser, Srivastava, and red cell distribution width (RDW) indices were evaluated at conventional cutoffs. Sensitivity analyses used ferritin < 30 ng/mL and C‐reactive protein (CRP) restrictions of ≤ 5 and ≤ 3 mg/L. All estimates were survey‐weighted.
Results
Among 3991 women, 507 had microcytosis. Ferritin‐defined noniron‐deficient microcytosis comprised 40.8% (95% CI, 35.5–46.2) and remained 37.0% and 33.6% after CRP restrictions of ≤ 5 and ≤ 3 mg/L. With ferritin ≥ 30 ng/mL, the corresponding proportions were 26.5%, 22.6%, and 20.2%. All four indices showed high sensitivity (92.9%–97.6%) but poor specificity (6.7%–35.3%). RDW had the highest specificity but still misclassified most noniron‐deficient cases.
Conclusions
Classic CBC indices had limited utility as standalone triage tools for ferritin‐defined microcytosis. Ferritin‐based assessment, interpreted in the relevant clinical and inflammatory context, should remain central. Persistent microcytosis without evidence of reduced iron stores should prompt diagnostic reconsideration and, when appropriate, hemoglobinopathy‐aware evaluation.