Abstract
In health, an efficient negative feedback mechanism maintains serum thyroid hormone concentrations within an exquisitely controlled narrow range. Therefore any change that occurs to thyroid hormones in intrinsic thyroid disease is concordant and easy to interpret. Optimal functioning of the many tissues they influence is thereby facilitated. The situation in acute illnesses is different. Mechanisms that operate in these circumstances influence the hypothalamic-pituitary-thyroid axis and its components producing thyroid test results, which are discordant, do not fit recognizable patterns and are difficult to interpret. The yield of abnormalities is also low (about 7%). As many studies indicate, thyroid tests are expensive and consume large amounts of the hospital budget and resources of hospital laboratories. Other studies have shown that when abnormalities are detected, clinicians do not intervene or follow up these subjects. Therefore the clinical utility of thyroid testing in acutely ill patients is debatable. Interventions to change requestor behaviour with regard to thyroid testing in acutely ill subjects and the success of some audit and educational interventions are worthy of note. Thyroid testing in acutely ill patients is often an expensive distraction and is of limited clinical value. Targeted thyroid testing should be offered in this group only to those with: (a) symptoms or signs of thyroid disease e.g. goiter or orbitopathy; (b) risk factors for thyroid disease, previous or family history of thyroid disease; (c) taking drugs which potentially affect thyroid function e.g. thyroxine replacement therapy, amiodarone, lithium, mechanistic target of rapamycin (mTOR) inhibitors, interferon, alemtuzumab etc; (d) unexplained tachydysrhythmias.
Highlights
The relationship between the two biologically active thyroid hormones, free thyroxine and free triiodothyronine, and thyroid stimulating hormone (TSH), the pituitary hormone that controls them, is tightly preserved in many diverse physiological and pathological conditions
FT4 and fT3 were low in 3.5% of the total group. 2.1% were given specific treatment for hypothyroidism or hyperthyroidism as thyroid tests were suggestive of intrinsic thyroid
Non thyroid illness syndrome (NTIS) was initially described in critically ill patients in Intensive Therapy units (ITU), there is accumulating evidence that NTIS occurs in subjects who are acutely but not critically ill i.e. not requiring ITU treatment (Table 2) [30,31,32,33]
Summary
The relationship between the two biologically active thyroid hormones, free thyroxine (fT4) and free triiodothyronine (fT3), and thyroid stimulating hormone (TSH), the pituitary hormone that controls them, is tightly preserved in many diverse physiological and pathological conditions. Within biochemistry the estimate of unnecessary tests is even higher at between 26–98% [15] In this regard, the clinical utility of laboratory diagnostic pathways needs to be highlighted, in thyroid testing [16]. The clinical utility of laboratory diagnostic pathways needs to be highlighted, in thyroid testing [16] These pathways are helpful in differentiating between the causes of frequently presenting clinical syndromes and in investigating rare or complex syndromes, which clinicians do not see often. They will have the potential to inform the clinician of conflicting or potentially confusing pre-analytical circumstances, when used within hospital electronic data systems These pathways would have advised against thyroid testing in acutely ill patients in the setting of the Acute Medical Admissions Unit – unless specific indications or criteria were fulfilled.
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