Abstract
It is well known that thyroid dysfunction increases with age. This study is aimed to determine reference intervals, in males and females, suitable for thyroid disease exploration during adult life using routinely collected serum thyrotropin (TSH) data in a tertiary center from 2007 to 2018. Over 11 years, 295,775 TSH levels were measured in a single lab. Among the 156,025 TSH results available for analysis, 90,538 values were from female subjects, 82,019 were from patients aged >60 years and 26,825 were from patients aged >80 years. By using an indirect approach, we determined reference values of TSH adapted to age and sex, and we then evaluated the proportion of patients who would have been reclassified with these reference values. The median TSH ranged from 1.2–1.4 mUI/L during the study period. The upper limit of reference range of TSH increased with age; in females the median to 97.5th percentile values increased continuously from the age of 30 years to the oldest age group. Using new calculated reference values in patients with TSH above the conventional upper-limit reference value (4 mUI/L), the proportion of results reclassified as within the reference interval among patients aged >60 years ranged, according to age group, from 50.5% to 65.1% of females and from 33.0% to 37.7% of males. The use of TSH age-specific and sex-specific upper-limit reference values led to the reclassification of a great number of samples, notably among women. This suggests that age-specific TSH upper-limit reference intervals in daily practice should be used in order to avoid misclassification.
Highlights
The increasing age of the general population represents a new challenge for endocrinologists and caregivers, since it is well known that the occurrence of thyroid dysfunction increases with age and is mostly present in females [1,2,3,4,5,6]
A major question deriving from the change of TSH with age is to decide whether or not TSH reference intervals need to be adapted to the most elderly in order to evaluate their thyroid function
This has been explored by Katayev et al, who reported that a TSH reference interval obtained from “big data” led to very similar results compared to findings from a healthy population tested for antithyroid antibodies [11]
Summary
The increasing age of the general population represents a new challenge for endocrinologists and caregivers, since it is well known that the occurrence of thyroid dysfunction increases with age and is mostly present in females [1,2,3,4,5,6]. Two different approaches exist to define reference intervals: the direct approach is based on the recruitment and selection of control subjects [9], whereas the indirect approach is based on the analysis of available data from routine testing [10] The International Federation of Clinical Chemistry (IFCC) has published recommendations to encourage the use of indirect methods to define reference interval [10] This has been explored by Katayev et al, who reported that a TSH reference interval obtained from “big data” led to very similar results compared to findings from a healthy population tested for antithyroid antibodies [11]. They concluded that estimation of reference interval using stored test results is accurate and reproducible
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