Prevalence of thyroid dysfunction and autoimmunity in the older population and implications of age-specific reference ranges

- Serum TSH reference ranges provided by your lab are not age-specific
- The absence of cardiovascular diseases in relation to mild thyroid dysfunction in the older population can be due to misclassification
- The prevalence of mild thyroid dysfunction is comparable between younger and older individuals, when age-specific reference ranges are used
- Age-specific TSH reference ranges should be determined and applied in daily practice

ObjectiveTo investigate the prevalence of thyroid dysfunction and autoimmunity (TAI) and to determine age-specific reference ranges in individuals < 60 and ≥ 60-year-old. Furthermore we investigated the impact of the age-specific reference ranges on the prevalence of thyroid dysfunction.DesignRetrospective analysis of laboratory data collected over six months in 2015, mainly from individuals consulting the outpatient clinic.MethodData from 676 individuals were withheld, after having applied strict exclusion criteria to avoid confounders. After exclusion of individuals with TAI (TPO-abs > 60 kIU/L) and/or outliers, data of 547 individuals were used to determine age-specific reference ranges. The prevalence of subclinical hypothyroidism (SCH) and subclinical hyperthyroidism (sch) was determined according to the reference ranges from the commercial assay and also according to the calculated age-specific reference ranges. From our study population.ResultsFrom the 676 individuals included, 559 (83%) were < 60 year-old and 117 (17%) ≥ 60 year-old. The prevalence of sch and TAI was comparable between both groups (8.6% vs. 13.7% and 15.4% vs. 20.5% respectively). The prevalence of SCH was significantly higher in individuals ≥ 60 years, compared to that in individuals < 60 years (14.5% vs. 5.4%; p < 0.001). The calculated 2.5 and 97.5 percentile for the age-specific TSH range was 0.24 and 4.4 mIU/L in individuals < 60 years and 0.15 and 8.2 mIU/L in individuals ≥ 60 years. When these the prevalence of sch and SCH was then determined on the basis of the age-specific reference ranges, the prevalence of SCH significantly decreased in individuals ≥ 60 years (14.5% to 5%; p = 0.027) and it then became comparable with that in individuals < 60 years (5% vs. 3%).ConclusionsThe prevalence of SCH was higher in individuals ≥ 60 years, compared to that in individuals < 60 years, but when age-specific TSH reference ranges were used, it was comparable between both study groups. In order to avoid misclassification in older individuals, it is important to use age-specific reference ranges in daily clinical practice