Making sense of thyroid function tests

Abstract

Background: Thyroid disorders are second only to diabetes mellitus among endocrine problems encountered in practice. Many patients with thyroid disorders tend to present with nonspecific symptoms to clinicians in different specialties, who are often quick to request for a thyroid function test. Although interpretation of the results of most thyroid function tests (TFTs) is straightforward, in a small number of situations the results seem to point in different directions, thereby producing clinical confusion. Knowledge of the different patterns of TFTs and their causes will help clinicians to properly manage their patients and avoid unnecessary, and often expensive further investigations.

Objective: To highlight the causes of the different patterns of abnormal thyroid function tests seen in clinical practice and to provide a practical approach to the evaluation of patients with such results.

Method: We searched PubMed, Google scholar and Medline for articles written in English on the interpretation and pattern of thyroid function tests.

Result: Interpretation of the results of most TFTs is straightforward especially when combined measurements (TSH with T4 or T3 or both) are ordered. Careful clinical reassessment of thyroid status and consideration of possible confounding factors such as pregnancy, intercurrent (non-thyroidal) illness or drug therapy will readily identify the cause of such apparently discordant TFTs.

Conclusion: A sound knowledge of the conditions that can be associated with different patterns of TFTs will go a long way in guiding the choice of additional investigations and allowing a correct diagnosis, thus avoiding inappropriate treatment.

Keywords: Thyroid function tests (TFTs), patterns of abnormal TFTs, non-thyroidal illness