Therefore, TSH has traditionally been recommended as a frontline screening test for thyroid dysfunction, because relatively modest changes in TH levels are associated with marked excursions in TSH. However, the population reference ranges for TH are relatively wide (especially for T4) and changes in TH levels sufficient to render a patient hypo- or hyperthyroid might not necessarily be associated with numerically abnormal T4 or T3 levels (as occurs in so-called вЂsubclinicalвЂ™ hypo- or hyperthyroidism). 3 Changes in thyroid status are typically associated with concordant changes in TH and TSH levels (eg raised T4 and T3 with suppressed TSH in thyrotoxicosis low T4 and T3 with elevated TSH in hypothyroidism). In any given individual, TH (thyroxine, T4 triiodothyronine, T3) levels remain relatively constant and reflect the вЂset-pointвЂ™ of the hypothalamicвЂ“pituitaryвЂ“thyroid (HPT) axis in that individual. Here, we highlight the main causes of commonly encountered patterns of abnormal thyroid function, including so-called вЂanomalous/discordant TFTsвЂ™, and propose a simple strategy for their investigation. However, in an important subgroup of patients, they can seem confusing, either by virtue of being discordant with the clinical picture (eg inability of supraphysiological levothyroxine therapy to suppress thyroid stimulating hormone (TSH thyrotropin) in hypothyroidism) or because different assay results appear to contradict each other (eg raised thyroid hormone (TH) levels, but with non-suppressed TSH or low TH levels with inappropriately normal or low TSH) ( Fig 1). In most cases the results of TFTs are straightforward and present a familiar pattern that is easy to recognise. 1, 2 Accordingly, a high clinical index of suspicion is required, and confirmation of diagnosis usually depends on accurate measurement and interpretation of thyroid function tests (TFTs). Although thyroid disease in its most florid form is easily recognised, patients often manifest symptoms and/or signs that are non-specific, and present to clinicians in many different specialties. Referral to a specialist laboratory and/or endocrine service is required when anomalous or discordant TFTs cannot be readily explained by confounding intercurrent illness, medication or assay interferenceДisorders of thyroid function are common (estimated UK prevalence is 1вЂ“4%). Screening for interference in thyroid hormone (T4 and T3) and/or thyrotropin (TSH) laboratory assays should be considered in any patient with apparently anomalous or discordant TFTs The results of thyroid function tests (TFTs) must always be interpreted in light of the clinical status of the patient: hypothyroid, euthyroid or hyperthyroidДЄwareness of the conditions and/or disorders that can be associated with different patterns of TFTs guides further investigation and managementД¬onfounding factors that may might influence thyroid status (eg intercurrent non-thyroidal illness or medications) should be excluded before embarking on further biochemical, radiological or genetic testing

Low t3 results