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Reference Intervals of Serum TSH from Mixed Distributions Using Truncation Points and the Kolmogorov-Smirnov Distance by Sibtain Ahmed, Jakob Zierk, Aysha H. Khan, Lena Jafri, Hafsa Majid, Farooq Ghani, Imran Siddiqui

Background: Serum TSH reference intervals (RIs) are methodology, population, and age specific. However, the ethical and practical challenges restrict the establishment of pediatric RIs using conventional approaches and advocates the use of indirect data mining-based algorithms. This study was carried out to estimate the reference interval of neonatal serum TSH in Pakistani population using an indirect approach.
Methods: A data mining of serum TSH results of neonates (≤ 1 month of age) from 2013 - 2018 was done. Two subgroups on the basis of age from birth to 5 days and 6 - 30 days were assessed. The German study group’s pre-validated indirect algorithm ‘KOSMIC’ was utilized for the statistical analysis.
Results: A total of non-duplicate 82,299 neonatal serum TSH tests were retrieved over a period of 6 years, including 88% (n = 70,788) aged 0 - 5 days and 12% (n = 11,511) ranging from 6 days to 1 month. The estimated RIs for the first age partition was 0.7 (90% CI 0.6 - 0.8) to 15.5 (90% CI 12.9 - 16.2) and for the second group 0.7 (90% CI 0.5 - 0.9) to 7.8 (90% CI 6.1 - 9.9) µIU/mL.
Conclusions: This study revealed age related trends in serum TSH. The study advocates the need for population specific RIs owing to the significant variations noted on comparison with previously published literature. Precise RIs become vital particularly when serum TSH is undertaken as a confirmatory test for presumptive positive results on newborn screening for congenital hypothyroidism.

DOI: 10.7754/Clin.Lab.2021.210833