title: Reliability of thyroglobulin in serum compared with urinary iodine when assessing individual and population iodine nutrition status.
abstract: The occurrence of thyroid disorders relies on I nutrition and monitoring of all populations is recommended. Measuring I in urine is standard but thyroglobulin in serum is an alternative. This led us to assess the reliability of studies using serum thyroglobulin compared with urinary I to assess the I nutrition level and calculate the number of participants needed in a study with repeated data sampling in the same individuals for 1 year. Diet, supplement use and life style factors were assessed by questionnaires. We measured thyroglobulin and thyroglobulin antibodies in serum and I in urine. Participants were thirty-three Caucasians and sixty-four Inuit living in Greenland aged 30-49 years. Serum thyroglobulin decreased with rising I excretion (Kendall's τ -0·29, P=0·005) and did not differ with ethnicity. Variation in individuals was lower for serum-thyroglobulin than for urinary I (mean individual CV: 15·1 v. 46·1 %; P<0·01). It required 245 urine samples to be 95 % certain of having a urinary I excretion within 10 % of the true mean of the population. For serum-thyroglobulin the same precision required 206 samples. In an individual ten times more samples were needed to depict I deficiency when using urinary I excretion compared with serum-thyroglobulin. In conclusion, more participants are need to portray I deficiency in a population when using urinary I compared with serum-thyroglobulin, and about ten times more samples are needed in an individual. Adding serum-thyroglobulin to urinary I may inform surveys of I nutrition by allowing subgroup analysis with similar reliability.
authors.affiliation: 1Arctic Health Research Centre,Institute of Clinical Medicine,Aalborg University Hospital,9000 Aalborg,Denmark.
authors.forename: Stig
authors.initials: S
authors.lastname: Andersen
authors.affiliation: 1Arctic Health Research Centre,Institute of Clinical Medicine,Aalborg University Hospital,9000 Aalborg,Denmark.
authors.forename: Paneeraq
authors.initials: P
authors.lastname: Noahsen
authors.affiliation: 2Department of Geriatric and Internal Medicine,Aalborg University Hospital,9000 Aalborg,Denmark.
authors.forename: Louise
authors.initials: L
authors.lastname: Westergaard
authors.affiliation: 1Arctic Health Research Centre,Institute of Clinical Medicine,Aalborg University Hospital,9000 Aalborg,Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Laurberg
mesh_terms: D000328:Adult; D000906:Antibodies / Q000097:blood; D015415:Biomarkers / Q000097:blood; D003677:Deficiency Diseases / Q000097:blood* / Q000208:ethnology / Q000652:urine; D004032:Diet; D019587:Dietary Supplements; D005260:Female; D006116:Greenland; D006801:Humans; D004930:Inuit; D007455:Iodine / Q000097:blood / Q000172:deficiency* / Q000652:urine; D008297:Male; D008875:Middle Aged; D009752:Nutritional Status; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D013954:Thyroglobulin / Q000097:blood*; D044465:White People
chemical_list: D000906:Antibodies; D015415:Biomarkers; D013954:Thyroglobulin; D007455:Iodine
keywords:  TGAb thyroglobulin antibodies;  UIC urinary iodine concentration;  s-TG serum thyroglobulin; Iodine nutrition study design; Number of samples needed; Reliability of iodine nutrition surveillance; Thyroglobulin; Urinary iodine excretion