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 reference values 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 pattern of association between them within a class. Results: Euthyroid population has FT4 and TSH (14.83–14.90 pmol/ml) and (2.40–2.43 μIU/ml) respectively as 95% Confidence Interval and there is no association between them (r=-0.056; sig. 0.000). Major bulk of abnormal thyroid function (98.15%) is constituted by 4 classes namely Primary Hypothyroid, Primary Hyperthyroid, Compensated Hypothyroid and Compensated Hyperthyroid. The MDs of hormones between groups/ classes are significant (sig.<0.009) in 91.67% (66 of 72) equations and documented FT4 alone can identify 5 classes (Euthyroid, Primary Hyperthyroid, Compensated Hypothyroid, Compensated Hyperthyroid and Secondary Hypothyroid) as their FT4 are significantly different from those of all rest 8 classes and for TSH it is true in only 2 classes (Primary Hypothyroid and Primary Hyperthyroid). Correlations between FT4 and TSH in all 9 classes with abnormal functions are different and none is strong (r<-0.5) therefore only TSH should not be used in diagnostic or follow-up setting. Conclusion: Paired Test can defines 9 classes with class specific FT4 or/and TSH ranges and their correlation pattern. 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.