Indirect estimation of reference intervals for thyroid parameters using advia centaur XP analyzer

Abstract

Background: The aim of this study was to determine the reference intervals (RIs) for thyroid stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3) and FT3/FT4 ratio using indirect methods.
 Methods: We analysed 1256 results TSH, FT4 and FT3 collected from a laboratory information system between 2017 and 2021. All measurements were performed on a Siemens ADVIA Centaur XP analyser using the chemiluminescent immunoassay. We calculated the values of the 2.5th and 97.5th percentiles as recommended by the IFCC (CLSI C28-A3).
 Results: The RIs derived for TSH, FT4, FT3 and FT3/FT4 ratio were 0.34-4.10 mIU/L, 11.3-20.6 pmol/L, 3.5-6.32 pmol/L and 0.21-0.47, respectively. We found a significant difference between calculated RIs for the TSH and FT4 and those recommended by the manufacturer. Also, FT3 values were significantly higher in the group younger than 30 years relative to the fourth decade (5.26 vs. 5.02, p=0.005), the fifth decade (5.26 vs. 4.94, p=0.001), the sixth decade (5.26 vs. 4.87, p˂0.001), the seventh decade (5.26 vs. 4.79, p˂0.001) and the group older than 70 years old (5.26 vs. 4.55, p˂0.001). Likewise, we found for TSH values and FT3 / FT4 ratio a significant difference (p <0.001) between different age groups.
 Conclusions: The establishing RIs for the population of the Republic of Srpska were significantly differed from the recommended RIs by the manufacturer for TSH and FT4. Our results encourage other laboratories to develop their own RIs for thyroid parameters by applying CLSI recommendations.

Reference intervals for thyroid hormones for the elderly population and their influence on the diagnosis of subclinical hypothyroidism

“…We used the Tukey method to remove outliers (13). The median, first quartile (Q1), third quartile (Q3), and interquartile range (IQR) were calculated.…”

“…We extracted 24,780 subjects from the laboratory information system. The exclusion criteria were as follows: subjects with missing information (including TSH, TT3, TT4, FT3, FT4, sex, and age), TSH out of detection range (>150 mIU/L and <0.008 mIU/L), <18 years old, pregnant females, and abnormal anti-thyroid peroxidase antibody (>60,000 IU/L) or anti-thyroglobulin antibody (>41,000 IU/L) [13] . Finally, 24,609 subjects were included in the study.…”