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La Rivista Italiana della Medicina di Laboratorio 2020 Giugno;16(2):101-7

DOI: 10.23736/S1825-859X.20.00064-X


language: Italian

TSH reference intervals in Italy: a two-site geoepidemiological study

Renato TOZZOLI 1 , Francesca DI SERIO 2, Paolo METUS 3, Vincenzo BRESCIA 4

1 Unità di Endocrinologia, Policlinico San Giorgio, Pordenone, Italia; 2 Laboratorio di Patologia Clinica, Policlinico Consorziale, Bari, Italia; 3 Laboratorio di Patologia Clinica, Ospedale S. Maria degli Angeli, Pordenone, Italia; 4 Medicina di Laboratorio, Azienda Ospedaliera Cardinale Panico, Tricase, Lecce, Italia

BACKGROUND: The measurement of concentration of the tireotropin (TSH) is the most reliable indicator of thyroid function: it has recently been proposed to use indirect methods based on ‘large data’ found in the computer systems database (LIS) of provincial/regional laboratories. These methods minimize the problems of the ‘a priori’ selection of the reference sample and allow to define the specific IR in base of epidemiological parameters (age, sex, race) and the immunometric method used.
METHODS: We conducted a study on SILs from two large laboratories, Pordenone and Bari. The number of individuals examined was 224,291 (132,446 females and 91,845 males) in the Bari study and 136,650 (92,168 females and 44,482 males) in the Pordenone study, for a total number of 360,941.
RESULTS: The overall distribution of the results shows a non-Gaussian trend in both locations, with a tail pointing towards the highest TSH values. The median of overall results is very similar in the two centers, as well as the median distinct by sex and the 2.5 and 97.5 centiles, which were used to express the reference range. The total median levels of TSH decrease progressively from 0-4 years to 85-104 years in the population of Pordenone (2.50 vs. 1.40 mUI/L; -1.10 mUI/L; P<0.01), while showing a trend only partly similar in Bari (2.82 vs. 1.51 mUI/L, -1.31; P<0.01), where they exhibit a different trend: progressive decrease to the age group 55-59 and then maintain up to the most advanced classes. This binomial trend is further confirmation of the role of iodine sufficiency or deficiency on TSH concentrations: the apparent contrast between the U-rate trend present in some countries, compared to the progressively decreasing trend evident in others, including Northern Italy, can be solved on the basis of the different iodic concentration of the population.
CONCLUSIONS: In conclusion, the TSH measurement method is the most important factor in defining analytical variability in the definition of TSH IRs; iodine deficiency is an important factor in the distribution of IRs, particularly for the impact on age; the laboratory must define its reference intervals on a local/regional basis, using indirect methods applied on it big data.

KEY WORDS: TSH; Reference intervals; Indirect method; Iodine status; Population studies

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