Subclinical Iron Deficiency in Non-Anemic Individuals: A Retrospective Analysis of Korean Health Examinees

Objectives: Non-anemic individuals may have undetected subclinical iron deficiency (SID). The aims of this study were to determine the prevalence of SID and identify the associated factors for SID. In addition, the screening performance of red blood cell (RBC) indices for SID in health check-ups was assessed.

Methods: This study was conducted with 16,485 non-anemic health examinees (3,567 males and 12,918 females) who underwent tests for iron variables (serum iron, total iron-binding capacity, ferritin, and iron saturation) at 16 health-promotion centers in 13 cities in Korea between January 2017 and June 2018. SID was defined as a decreased ferritin level (<24 µg/L in males and <15 µg/L in females) and either a decreased serum iron level (<44 µg/dL in males and <29 µg/dL in females) or a transferrin saturation of <20%.

Results: The prevalence rates of SID were 0.6 and 3.3% in males and females, respectively. In terms of age and sex, SID was most prevalent in males aged ≥70 years (7.8%) and females aged 15-49 years (7.6%). There were significant differences in the hemoglobin (Hb) level, white blood cell count, platelet count, mean corpuscular volume, mean corpuscular Hb (MCH), and RBC distribution width (RDW) between the SID and non-SID groups (p < 0.001). The factors associated with SID in males were older age (odds ratio, OR, 1.069, 95% confidence interval, CI, 1.03-1.109, p = 0.004), lower Hb (OR 0.58, 95% CI 0.345-0.976, p = 0.04), lower MCH (OR 0.433, 95% CI 0.298-0.629, p < 0.001), and higher RDW (OR 1.374, 95% CI 1.001-1.887, p = 0.049), while in females they were lower body mass index (BMI; OR 0.929, 95% CI 0.895-0.963, p < 0.001) and younger age (OR 0.954, 95% CI 0.945-0.963, p < 0.001), as well as lower Hb, lower MCH, and higher RDW. The AUC for the MCH (0.877, 95% CI 0.793-0.960 in males; 0.872, 95% CI 0.853-0.890 in females) indicates that the MCH at cut-offs of 29.2 and 29.3 pg are the best discriminators of SID in males and females, respectively (p < 0.001).

Conclusions: Reproductive-age females with a lower BMI and elderly males are high-risk groups for SID. MCH is a reliable RBC index for the screening of SID. For the population with defined risk factors, including females with lower BMI and elderly males, screening for SID is needed to prevent the development of anemia.