8124 Prevalence and Characteristics of Patients with Hypothyroidism in the Danish Blood Donor Study
Authors: Frisk N L , Shorter J R , Pedersen O B , Dalgaard L T 
Published: October 2024

Abstract
Disclosure: N.L. Frisk: None. J.R. Shorter: None. O.B. Pedersen: None. L.T. Dalgaard: None.
Introduction: While impaired thyroid function leading to subclinical hypothyroidism and overt hypothyroidism is common in Denmark, the knowledge about the paths by which patients’ progress to impaired thyroid function is limited. Undiagnosed hypothyroidism as well as subclinical hypothyroidism constitute serious risk factors for development of cardio metabolic disease. The Danish Blood Donor Study (DBDS) is a large longitudinal cohort and biobank containing information and samples dating more than 10 years back. Blood donors donate blood every 3-6 months and each time provide a sample for research. Research question: The aim of the study was to obtain up-to-date information about prevalence and characteristics of patients with hypothyroidism in a Danish longitudinal cohort of blood donors. Methodology: The study employed a cross-sectional design. Hypothyroidism was defined based on at least two prescriptions of levothyroxine (LT4) and used for calculations of prevalence. Case numbers were compared to all controls that were currently not being prescribed LT4 nor anti-thyroid drugs (carbimazole, propylthiouracil, thiamazole). We compared cases of hypothyroidism to two different control (ctrl) groups: 1) All the participants of the DBDS having TSH levels in the normal range, and 2) Normothyroid participants matched to hypothyroid cases based on age and sex. Incidence was determined based on DBDS participants developing hypothyroidism after being enrolled into the DBDS during a 10-year follow-up. Men and women were compared separately among cases and controls. Students’ t-test was used to compare cases and controls, and corrected using Bonferroni. Major results: There were 3397 cases of hypothyroidism and 153791 ctrl subjects in the DBDS, giving a prevalence of 2.2%. 85% of cases were female, while among ctrl 50% were female. Average age of cases was 52±13 years (mean±SD) for women and 58±13 for men, while ctrls were 45±13 and 48±14 years, respectively (both P&lt;0.001). BMI among cases were: 25.8±4.7 for women and 26.8±3.9 kg/m2, while cases were 25.1±4.4 and 26.0±3.6, respectively (both P&lt;0.001). TSH levels were, for female cases: 4.6±4.0 iu/mL and 5.7±4.9 for men, while ctrls were 1.8±1.1 and 1.7±1.1, respectively (both P&lt;0.001). Free (F) T4 levels were, for female cases: 14.4±6.4pmol/L and male: 14.0±4.6, while ctrls were: 14.8±4.5 and 15.0±3.9 respectively (P&lt;0.003 for females, P&lt;0.0001 for males), while FT3 levels were for cases: 4.3±1.7 and 4.3±1.4 pmol/L and 4.5±2.0 and 4.7±1.5 for ctrls (both P&lt;0.0001). Conclusion: Hypothyroidism is less prevalent among blood donors than reported in the general Danish population, which is accordance with ‘the healthy donor’ bias. Hypothyroid donors were on average older and with higher BMI than normothyroid controls. Donors with hypothyroidism were generally well regulated, but despite that FT4 and FT3 levels were lower than ctrls.
Presentation: 6/1/2024