Mean corpuscular Hb and red cell distribution width for early screening of non-anaemic Fe deficiency in children: a retrospective study.

Fe deficiency (ID) is a common nutritional disorder, especially among children and women of reproductive age. Detecting ID before it progresses to Fe deficiency anaemia (IDA) is critical for prevention. This study assessed mean corpuscular Hb (MCH) and red cell distribution width (RDW) as complete blood count (CBC) based markers for early non-anaemic Fe deficiency (NAID). We retrospectively analysed records of children aged 2 months to 6 years who underwent regular general health checks at Fujian Provincial Maternal and Child Health Hospital between July 2022 and July 2024. ID was defined by serum ferritin < 15 µg/l. Children with thalassemia, inflammatory conditions (C-reactive protein > 5 mg/l) or incomplete data were excluded. Logistic regression was used to evaluate associations between CBC indices and ID. Model discrimination was assessed by the area under the receiver operating characteristic curve and externally validated using National Health and Nutrition Examination Survey (August 2021-August 2023, Cycle 12) data. A total of 2018 children were included (training: n 1413, testing: n 605; external validation: n 232). MCH (OR = 0·63; 95 % CI, 0·52, 0·76; P < 0·001) and RDW (OR = 1·44; 95 % CI, 1·16, 1·79; P = 0·001) were independent predictors of ID. The model showed consistent performance, with AUC of 0·77 (training), 0·81 (testing) and 0·87 (validation). MCH and RDW are practical markers for early NAID detection in Chinese and US children, offering a valuable tool for any setting with an automated haematology analyser, particularly when access to advanced Fe studies is restricted.