Assessment of Thyroid Function Status by Paired Test

Aim and Methods: To understand the utility of paired FT4 and TSH test in determining functional
status of Thyroid in diagnostic and follow up settings, we studied 34159 test results. We divided the
population into all 9 nine possible classes by using the laboratory reference ranges of the FT4 and
TSH. Then we determined class frequency, reference ranges of FT4 and TSH for each class, their
Mean Differences (MD) between classes and correlation between FT4 and TSH within a class.
Results: Our Euthyroid population having normal FT4 and TSH size is of 24722. The 95% Confidence
Interval of mean of their FT4 and TSH are (14.83–14.90 pmol/ml) and (2.40–2.43 μIU/ml) respectively
and their correlation (r value) is -0.056; sig. 0.000 only. The 8 classes with abnormal status are with 4
pairs of hypo and hyperthyroximic state - namely Primary Hypo & Hyperthyrodism; Compensated
Hypo & Hyperthyrodism; Secondary Hypo & Hyperthyrodism and Isolated Hypo & Hyperthyroximia.
Major bulk of abnormal thyroid function (98.15%) is constituted by 4 classes namely Primary
Hypothyroid, Primary Hyperthyroid, Compensated Hypothyroid and Compensated Hyperthyroid. The
rest classes are rare.
FT4 of a class has significant mean difference from those of all the rest 8 classes (sig <.002)
excepting in 2 out of total 36 situations. And in these 2 pairs with non-significant MD for FT4 have
significant MDs for their TSH (sig.000).
None of 8 classes with abnormal functions have strong correlation between FT4 and TSH (r < -0.5).
Moderate negative association is documented only in 2 classes – Primary Hypothyroidism (r =-0.445;
Sig. 0.000) and Primary Hyperthyroidism (r =-0.386; Sig. 0.000). There is no correlations between
them in euthyroid class (r=-0.056; sig. 0.000). Therefore, TSH alone should not be used to determine
functional status in diagnostic or follow-up settings.
Conclusion: Paired Test can define 9 classes with class specific FT4 and TSH ranges and their
correlation patterns. We opine, to use this tool to determination of functional status and utilize
reference range of FT4 of Euthyroid as the treatment target for cases with abnormal function.