IMPE Abstracts

Introduction and aim: Establishing reference intervals (RI) is particularly problematic for constituents with a large diversity of existing biological variation and inter-population differences, as is observed for thyroid hormones and TSH. An alternative to this problem is to use indirect methods, with a large data pools base of results. Analyze thousands of subjects including some pathologic results is statistically stronger than 120 subjects that assume healthy. Our aim was to establish RI using indirect methods compare them with bibliography and verify RI results in our population.

Material and methods: TSH, fT4, TT3 and TT4 data were collected from 19842 patients between January 2020 and December 2021. General laboratory data was evaluated as well as antithyroid antibodies positivity. Inpatients and patients with pathologic results were excluded. TSH, TT3 and fT4 were tested using Architect i4000-Abbott and TT4 with Immulite 2000XPi-Siemens. Remain 4861 patients were divided in three group: A :≤12 months (n:551), B:13 months to 7 years old (n:1347) and C: 8 to 18 years old (n:2963). RI were calculated in each group by two methods, Hoffman adapted method¹ and a non parametric with logarithmic transformation (CLSI28 A3). Outliers were detected and excluded by Tukey². 20 serum samples from each age group (B and C) having pre-surgical laboratory test were used to verify calculated RI. Their clinical records were look over by a specialist to exclude pathologies and drugs that may affect thyroid profile. Outliers were detected and excluded by Tukey². Data was processed as recommended by CLSI EP28-A3c.

Results:

Conclusion: RI calculated by indirect methods Hoffman and CLSI28A3 are similar than RI previously published³ obtained by direct methods. Thus, indirect methods find to be good alternative when a healthy population is not easily accessible. Verification wasn’t successful in group B TT3 with both methods; this observation is associated to a higher general mean. Indirect methods include some subjective decision points; it´s important to carry out a complete verification before being applied.

1. Katayev A (2010), doi:10.1309/AJCPN5BMTSF1CDYP 2. Tukey (1977) 3. Bailey D (2013), doi:10.1373/clinchem.2013.204222