| Thyroid Feedback Quantile-based Index | |
|---|---|
| Synonyms | TFQI, PTFQI |
| Reference range | –0.74 – +0.74 |
| Test of | Sensitivity of TSH-producing pituitary cells to thyroid hormones; also a marker for the set point of thyroid homeostasis |
The Thyroid Feedback Quantile-based Index (TFQI) is a calculated parameter for thyrotropic pituitary function. It was defined to be more robust to distorted data than established markers including Jostel's TSH index (JTI) and the thyrotroph thyroid hormone sensitivity index (TTSI).
The TFQI can be calculated with
from quantiles of FT4 and TSH concentration (as determined based on cumulative distribution functions). [1] Per definition the TFQI has a mean of 0 and a standard deviation of 0.37 in a reference population. [1] This explains the reference range of –0.74 to + 0.74.
| Parameter | Lower limit | Upper limit | Unit |
| TFQI (PTFQI) | –0.74 | +0.74 | |
Higher values of TFQI are associated with obesity, metabolic syndrome, impaired renal function, diabetes, and diabetes-related mortality. [1] [2] [3] [4] [5] [6] [7] In a large population of community-dwelling euthyroid subjects the thyroid feedback quantile-based index predicted all-cause mortality, even after adjustment for other established risk factors and comorbidities. [8]
A cross-sectional study from Spain observed increased prevalence of type 2 diabetes, atrial fibrillation, ischemic heart disease and hypertension in persons with elevated PTFQI. [9]
Serum Concentrations of Adipocyte Fatty Acid-Binding Protein (A-FABP) are significantly correlateted to TFQI, suggesting some form of cross-talk between adipose tissue and HPT axis. [10]
TFQI results are also elevated in takotsubo syndrome, [11] potentially reflecting type 2 allostatic load in the situation of psychosocial stress. Reductions have been observed in subjects with schizophrenia after initiation of therapy with oxcarbazepine [12] and quetiapine, [13] potentially reflecting declining allostatic load.
Despite positive association to metabolic syndrome and type 2 allostatic load a large population-based study failed to identify an association to risks of dyslipidemia and non-alcoholic fatty liver disease (NAFLD). [14]
Hyperthyroidism is the condition that occurs due to excessive production of thyroid hormones by the thyroid gland. Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidism. Some, however, use the terms interchangeably. Signs and symptoms vary between people and may include irritability, muscle weakness, sleeping problems, a fast heartbeat, heat intolerance, diarrhea, enlargement of the thyroid, hand tremor, and weight loss. Symptoms are typically less severe in the elderly and during pregnancy. An uncommon but life-threatening complication is thyroid storm in which an event such as an infection results in worsening symptoms such as confusion and a high temperature; this often results in death. The opposite is hypothyroidism, when the thyroid gland does not make enough thyroid hormone.
Hypothyroidism is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormones. It can cause a number of symptoms, such as poor ability to tolerate cold, a feeling of tiredness, constipation, slow heart rate, depression, and weight gain. Occasionally there may be swelling of the front part of the neck due to goitre. Untreated cases of hypothyroidism during pregnancy can lead to delays in growth and intellectual development in the baby or congenital iodine deficiency syndrome.
Thyroid-stimulating hormone (also known as thyrotropin, thyrotropic hormone, or abbreviated TSH) is a pituitary hormone that stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3) which stimulates the metabolism of almost every tissue in the body. It is a glycoprotein hormone produced by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid.
Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.
Thyroid hormone resistance (also resistance to thyroid hormone (RTH), and sometimes Refetoff syndrome) describes a rare syndrome in which the thyroid hormone levels are elevated but the thyroid stimulating hormone (TSH) level is not suppressed, or not completely suppressed as would be expected. The first report of the condition appeared in 1967. Essentially this is decreased end organ responsiveness to thyroid hormones. A new term "impaired sensitivity to thyroid hormone" has been suggested in March 2014 by Refetoff et al.
Thyroid storm is a rare but severe and life-threatening complication of hyperthyroidism. It occurs when overactive thyroid activity leads to hypermetabolism, the end result being death from cardiac arrest or multiple organ failure.
Thyroid function tests (TFTs) is a collective term for blood tests used to check the function of the thyroid. TFTs may be requested if a patient is thought to suffer from hyperthyroidism or hypothyroidism, or to monitor the effectiveness of either thyroid-suppression or hormone replacement therapy. It is also requested routinely in conditions linked to thyroid disease, such as atrial fibrillation and anxiety disorder.
Allostatic load is "the wear and tear on the body" which accumulates as an individual is exposed to repeated or chronic stress. The term was coined by Bruce McEwen and Eliot Stellar in 1993. It represents the physiological consequences of chronic exposure to fluctuating or heightened neural or neuroendocrine response which results from repeated or prolonged chronic stress.
The thyroid hormone receptor (TR) is a type of nuclear receptor that is activated by binding thyroid hormone. TRs act as transcription factors, ultimately affecting the regulation of gene transcription and translation. These receptors also have non-genomic effects that lead to second messenger activation, and corresponding cellular response.
The hypothalamic–pituitary–thyroid axis is part of the neuroendocrine system responsible for the regulation of metabolism and also responds to stress.
Euthyroid sick syndrome (ESS) is a state of adaptation or dysregulation of thyrotropic feedback control wherein the levels of T3 and/or T4 are abnormal, but the thyroid gland does not appear to be dysfunctional. This condition may result from allostatic responses of hypothalamus-pituitary-thyroid feedback control, dyshomeostatic disorders, drug interferences, and impaired assay characteristics in critical illness.
Myxedema coma is an extreme or decompensated form of hypothyroidism and while uncommon, is potentially lethal. A person may have laboratory values identical to a "normal" hypothyroid state, but a stressful event precipitates the myxedema coma state, usually in the elderly. Primary symptoms of myxedema coma are altered mental status and low body temperature. Low blood sugar, low blood pressure, hyponatremia, hypercapnia, hypoxia, slowed heart rate, and hypoventilation may also occur. Myxedema, although included in the name, is not necessarily seen in myxedema coma. Coma is also not necessarily seen in myxedema coma, as patients may be obtunded without being comatose.
Thyroid hormones are any hormones produced and released by the thyroid gland, namely triiodothyronine (T3) and thyroxine (T4). They are tyrosine-based hormones that are primarily responsible for regulation of metabolism. T3 and T4 are partially composed of iodine, derived from food. A deficiency of iodine leads to decreased production of T3 and T4, enlarges the thyroid tissue and will cause the disease known as simple goitre.
Hypothalamic disease is a disorder presenting primarily in the hypothalamus, which may be caused by damage resulting from malnutrition, including anorexia and bulimia eating disorders, genetic disorders, radiation, surgery, head trauma, lesion, tumour or other physical injury to the hypothalamus. The hypothalamus is the control center for several endocrine functions. Endocrine systems controlled by the hypothalamus are regulated by antidiuretic hormone (ADH), corticotropin-releasing hormone, gonadotropin-releasing hormone, growth hormone-releasing hormone, oxytocin, all of which are secreted by the hypothalamus. Damage to the hypothalamus may impact any of these hormones and the related endocrine systems. Many of these hypothalamic hormones act on the pituitary gland. Hypothalamic disease therefore affects the functioning of the pituitary and the target organs controlled by the pituitary, including the adrenal glands, ovaries and testes, and the thyroid gland.
Thyroid disease in pregnancy can affect the health of the mother as well as the child before and after delivery. Thyroid disorders are prevalent in women of child-bearing age and for this reason commonly present as a pre-existing disease in pregnancy, or after childbirth. Uncorrected thyroid dysfunction in pregnancy has adverse effects on fetal and maternal well-being. The deleterious effects of thyroid dysfunction can also extend beyond pregnancy and delivery to affect neurointellectual development in the early life of the child. Due to an increase in thyroxine binding globulin, an increase in placental type 3 deioidinase and the placental transfer of maternal thyroxine to the fetus, the demand for thyroid hormones is increased during pregnancy. The necessary increase in thyroid hormone production is facilitated by high human chorionic gonadotropin (hCG) concentrations, which bind the TSH receptor and stimulate the maternal thyroid to increase maternal thyroid hormone concentrations by roughly 50%. If the necessary increase in thyroid function cannot be met, this may cause a previously unnoticed (mild) thyroid disorder to worsen and become evident as gestational thyroid disease. Currently, there is not enough evidence to suggest that screening for thyroid dysfunction is beneficial, especially since treatment thyroid hormone supplementation may come with a risk of overtreatment. After women give birth, about 5% develop postpartum thyroiditis which can occur up to nine months afterwards. This is characterized by a short period of hyperthyroidism followed by a period of hypothyroidism; 20–40% remain permanently hypothyroid.
Thyroid's secretory capacity is the maximum stimulated amount of thyroxine that the thyroid can produce in a given time-unit.
The sum activity of peripheral deiodinases is the maximum amount of triiodothyronine produced per time-unit under conditions of substrate saturation. It is assumed to reflect the activity of deiodinases outside the central nervous system and other isolated compartments. GD is therefore expected to reflect predominantly the activity of type I deiodinase.
Jostel's TSH index, also referred to as Jostel's thyrotropin index or Thyroid Function index (TFI), is a method for estimating the thyrotropic function of the anterior pituitary lobe in a quantitative way. The equation has been derived from the logarithmic standard model of thyroid homeostasis. In a paper from 2014 further study was suggested to show if it is useful, but the 2018 guideline by the European Thyroid Association for the diagnosis of uncertain cases of central hypothyroidism regarded it as beneficial. It is also recommended for purposes of differential diagnosis in the sociomedical expert assessment.
SimThyr is a free continuous dynamic simulation program for the pituitary-thyroid feedback control system. The open-source program is based on a nonlinear model of thyroid homeostasis. In addition to simulations in the time domain the software supports various methods of sensitivity analysis. Its simulation engine is multi-threaded and supports multiple processor cores. SimThyr provides a GUI, which allows for visualising time series, modifying constant structure parameters of the feedback loop, storing parameter sets as XML files and exporting results of simulations in various formats that are suitable for statistical software. SimThyr is intended for both educational purposes and in-silico research.
The Thyrotroph Thyroid Hormone Sensitivity Index is a calculated structure parameter of thyroid homeostasis. It was originally developed to deliver a method for fast screening for resistance to thyroid hormone. Today it is also used to get an estimate for the set point of thyroid homeostasis, especially to assess dynamic thyrotropic adaptation of the anterior pituitary gland, including non-thyroidal illnesses.
