Evaluating thyroid function in the clinical laboratory

Background: Thyroid disorders are common in clinical medicine and laboratory confirmation is essential, especially in cases where overt signs and symptoms are absent. The measurement of thyroid-stimulating hormone (TSH) is recommended as the best indicator of thyroid function and is utilized along with thyroxine (T4) and in some circumstances triiodothyronine (T3). Aim: The aim is to evaluate the relationship between TSH and free T4 (FT4), and TSH and FT3. Methods: Thyroid function tests (TFTs) – TSH, FT4, and FT3 – performed in the Chemical pathology laboratory from February to December 2015 were retrieved from the laboratory information management system. Results were classified based on TSH results into suppressed, mildly suppressed, normal, mildly elevated and elevated, and correlated with FT3 and FT4 results. Results were also categorized as overt hyperthyroidism, subclinical hyperthyroidism, normal, subclinical hypothyroidism, overt hypothyroidism, and “others” and compared based on age and gender. Results: FT4 and FT3 correlate best with TSH at suppressed and elevated levels. Mean TSH was significantly higher in males than in females only in those with normal FT4 and TSH. TSH was significantly higher in the 41–60 age group, with females in this group having significantly higher levels as compared to males. Conclusions: There is an inverse correlation between FT4 and TSH, and FT3 and TSH, especially significant at suppressed and elevated levels of TSH. Highest TSH levels were observed in women in the 41–60 age cohort.