Iron Deficiency and Hypoferritinaemia in Patients with Subclinical Hypothyroidism: A Retrospective Observational Study

Abstract

Introduction: Iron acts as a cofactor in Thyroid Peroxidase (TPO) activity, and low iron levels can impact thyroid hormone metabolism. The function of ferritin and iron has been extensively documented in various studies in patients with Overt Hypothyroidism (OH), but their role in Subclinical Hypothyroidism (SH) remains largely unexplored. Aim: To evaluate the serum ferritin and iron levels in patients who have SH. Materials and Methods: A retrospective observational study was conducted between March 2018 and October 2018 at the Biochemistry Department of Nizam’s Institute of Medical Sciences, Hyderabad, Telangana, India. For the study, a total of 100 cases of SH were enrolled, and these patients were matched in terms of age and sex with 50 healthy controls. A fasting sample was obtained and analysed for serum ferritin, Total Iron Binding Capacity (TIBC), TT3, TT4, and Thyroid Stimulating Hormone (TSH). MedCalc software was used to perform statistical analysis. Results: In the SH group, there were 32 males (32%) and 68 females (68%); in the control group, there were 21 males (42%) and 29 females (58%). The median values of TT3 (nmol/L), TT4 (μg/ dL), and TSH (μIU/mL) were 1.55 (1.4-1.95), 7.8 (5.9-9.75), and 3 (1.9-3.75) for controls, and 1.4 (1.1-1.75), 6.85 (5.5-8.15), and 6.2 (4.8-8.05), respectively, for cases. In comparison to controls, the TSH level was significantly higher (p<0.0001) in cases. The median iron (μg/dL), ferritin (ng/mL), TIBC (μg/dL), and % saturation in cases were 56.5 (41.5-82), 110 (31.5-194.5), 329 (258-390), and 19 (11.25-26.75), respectively, while in controls they were 84 (68.5- 96.5), 195 (121.5-338.5), 233 (188.5-294), and 25 (18-37.5). There was a significant decrease in iron level (p<0.00001), % saturation (<0.00001), and ferritin level (p<0.00001), and a significant increase in TIBC (p<0.0001) in cases when compared to controls. Conclusion: In conclusion, the present study showed a significant negative correlation between SH and iron deficiency. Patients with this condition should be evaluated for ferritin and iron levels and treated appropriately to prevent hypothyroidism.