Goal and Methods: We reviewed 34159 test results to understand the usefulness of paired FT4 and TSH tests in assessing Thyroid functional status in diagnostic and follow-up settings. By using the laboratory comparison ranges of FT4 and TSH, we divided the population into all nine possible groups. Then we calculated the frequency of the classes, the FT4 and TSH reference ranges for each class, their mean differences (MD) between classes and the association within a class between FT4 and TSH. Results: The typical FT4 and TSH scale of our euthyroid population is 24722. The mean confidence interval of their FT4 and TSH is 95 percent (14.83-14.90 pmol / ml) and (2.40-2.43 μIU / ml) respectively, and their correlation (r value) is -0.056; sig. Just 0.000. Main Hypo & Hyperthyrodism; Compensated Hypo & Hyperthyrodism; Secondary Hypo & Hyperthyrodism and Isolated Hypo & Hyperthyroximia. The 8 groups of irregular status are with 4 pairs of hypo and hyperthyroximic state. 4 types, namely Primary Hypothyroid, Primary Hyperthyroid, Compensated Hypothyroid and Compensated Hyperthyroid, represent the main bulk of irregular thyroid activity (98.15 percent). The remaining classes are special. Class FT4 has a substantial mean difference from all 8 other classes (sig < .002), with the exception of 2 out of a total of 36 cases. And for their TSH, there are significant MDs in these 2 pairs with non-significant MD for FT4 (sig.000). There is a clear association between FT4 and TSH in none of the 8 groups of abnormal functions (r < -0.5). Only 2 classes of primary hypothyroidism (r = -0.445; Sig. 0.000) and primary hyperthyroidism (r = -0.386; Sig. 0.000) record a mild negative relation. They are not associated in the euthyroid class (r=-0.056; sig. 0.000). Therefore, in diagnostic or follow-up environments, TSH alone should not be used for assessing functional status. Conclusion: 9 classes with class-specific FT4 and TSH ranges and their correlation patterns can be identified by the Paired Test. We conclude that this tool should be used to assess functional status and use Euthyroid’s FT4 reference range as the treatment target for abnormally functioning cases.

Author(s) Details

Prof. Tofail Ahmed
Department of Endocrinology, Bangladesh Institute for Research and Rehabilitation in Diabetes, Endocrine and Metabolic Disorders, Dhaka, Bangladesh.

Professor Hajera Mahtab
Department of Endocrinology, Bangladesh Institute for Research and Rehabilit Disorders, Dhaka, Bangladesh.

Dr. Tania Tofail
Department of Endocrinology, Bhangabando Sheikh Mujibur Medical University, Dhaka, Bangladesh.

Md. A. H. G. Morshed
Endocrinology Laboratory, Diabetic Association of Bangladesh, Dhaka, Bangladesh.

Shahidul A. Khan
Endocrinology Laboratory, Diabetic Association of Bangladesh, Dhaka, Bangladesh.

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