title: Prevalence of thyroid dysfunction and autoimmunity in the older population and implications of age-specific reference ranges.
abstract: OBJECTIVE
  To 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.
  
  
  METHODS
  Retrospective analysis of laboratory data collected over six months in 2015, mainly from individuals consulting the outpatient clinic.
  
  
  METHODS
  Data from 676 individuals were withheld, after having applied strict exclusion criteria to avoid confounders. After exclusion of individuals with TAI (TPO-abs >60kIU/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.
  
  
  RESULTS
  From the 676 individuals included, 559 (83%) were <60year-old and 117 (17%) ≥60year-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 ≥60years, compared to that in individuals <60years (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 <60years and 0.15 and 8.2mIU/L in individuals ≥60years. 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 ≥60years (14.5% to 5%; p=0.027) and it then became comparable with that in individuals <60years (5% vs. 3%).
  
  
  CONCLUSIONS
  The prevalence of SCH was higher in individuals ≥60years, compared to that in individuals <60years, 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.
authors.affiliation: Department of Internal Medicine, Université Libre de Bruxelles (ULB), Rue Haute 322, 1000 Brussels, Belgium.
authors.forename: Flora
authors.initials: F
authors.lastname: Veltri
authors.affiliation: Endocrine Unit, Department of Clinical Chemistery of the Centre Hosptilalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Rue Haute 322, 1000 Brussels, Belgium.
authors.forename: Francisco Oliveira
authors.initials: FO
authors.lastname: Rocha
authors.affiliation: Geriatric Unit, Department of Clinical Chemistery of the Centre Hosptilalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Rue Haute 322, 1000 Brussels, Belgium.
authors.forename: Dominique
authors.initials: D
authors.lastname: Willems
authors.affiliation: Endocrine Unit, Department of Clinical Chemistery of the Centre Hosptilalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Rue Haute 322, 1000 Brussels, Belgium.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Praet
authors.affiliation: Department of Internal Medicine, Université Libre de Bruxelles (ULB), Rue Haute 322, 1000 Brussels, Belgium.
authors.forename: Lidia
authors.initials: L
authors.lastname: Grabczan
authors.affiliation: Department of Internal Medicine, Université Libre de Bruxelles (ULB), Rue Haute 322, 1000 Brussels, Belgium.
authors.forename: Pierre
authors.initials: P
authors.lastname: Kleynen
authors.affiliation: Endocrine Unit, Department of Clinical Chemistery of the Centre Hosptilalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Rue Haute 322, 1000 Brussels, Belgium.
authors.forename: Thierry
authors.initials: T
authors.lastname: Pepersack
authors.affiliation: Department of Internal Medicine, Université Libre de Bruxelles (ULB), Rue Haute 322, 1000 Brussels, Belgium. Electronic address: kris_poppe@stpierre-bru.be.
authors.forename: Kris
authors.initials: K
authors.lastname: Poppe
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015551:Autoimmunity / Q000502:physiology*; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood / Q000453:epidemiology; D007037:Hypothyroidism / Q000097:blood / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012189:Retrospective Studies; D013959:Thyroid Diseases / Q000097:blood / Q000453:epidemiology*; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000276:immunology / Q000503:physiopathology*; D013972:Thyrotropin / Q000097:blood*
chemical_list: D013972:Thyrotropin
keywords: Age-specific TSH reference ranges; Older; Thyroid function and autoimmunity