The thyroid is a butterflyshaped gland located in the neck that produces thyroid hormone. Measuring thyroid stimulating hormone is the first step. The interpretation of tft results however, can often be challenging. To educate on what each lab test represents, what are the variables involved with the each lab test, and what may influence any given lab test. How should we be interpreting thyroid test results.
If it is abnormal, free thyroxine should be measured. A thyroid panel consisting of thyroid stimulating hormone tsh and free thyroxine ft4 should form the first line of diagnostic tests. False high and low readings secondary to tbg alterations. It is also requested routinely in conditions linked. Blood tests for thyroid function tsh, total t4, free t3, tsi, and othersare an important part of diagnosing and treating thyroid disorders. Testing for thyroid dysfunction tsh is the first test to perform serum tsh level remains the single best test of thyroid function. Abnormal tft results guidance abnormal thyroid function. Testing for thyroid disease is indicated by either increased or decreased metabolism. In addition, a blood test can measure levels of hormones thyroxine t4 and triiodothyronine t3, and less often, a protein called thyroglobulin. The initial workup includes testing for thyroid stimulating hormone tsh with reflex to. Thyroid hormone is required for normal brain and somatic tissue development in.
In the patients with obvious features of hypothyroidism or hyperthyroidism thyroid function tests only confirm the diagnosis. Uk guidelines for the use of thyroid function tests. It releases hormones into your bloodstream that control how your body functions. For many reasons, the blood tests may not show the true picture and it is quite wrong to rely on them by themselves. Thyroid tests assess inherent thyroid gland function radioactive iodine uptake test is used to assess intrinsic function of the thyroid gland this test is not specific and the reference range should be adjusted based on local population this test is indirect measure of thyroid activity 21.
Jul 01, 2012 thyroid diseases are common and in most cases the interpretation of thyroid function tests is straightforward. Thyroid function tests tfts are a group of tests requested to help check how the thyroid gland is working, to diagnose thyroid gland disorders and to monitor the response of thyroid disorders to treatment. To perform a thyroid function test, a blood sample is drawn from a vein in your arm and collected in a tube. Tfts include measuring the amount of the thyroid hormones, thyroxine t4. We propose that if assays for thyrotropin, free t3, and free t4 are all done, knowledge of these. Topic in focus interpretation of thyroid function tests cmi. Radioactive iodine uptake is a test that measures how much iodine the thyroid gland absorbs and can be useful in determining if the thyroid is overactive or underactive. Also, evaluation of thyroid function in hospitalized patients can be complicated by other illnesses and medications. High levels of the hormone indicate an underactive thyroid. The thyroid s job is to make thyroid hormones, which are secreted into the blood and then carried to every tissue in the body.
Thyroxinet4 this test is used to evaluate thyroid function. Thyroid function tests are a series of blood tests used to measure how well your thyroid gland is working. These hormones are essential for normal growth, development and metabolic function. Interpretation of thyroid tests common tests to examine. T4 concentration is affected by nonthyroidal illness nti and certain medications e. Tsh secretion, in turn, is controlled through negative feedback by thyroid hormones see thyroid hormone synthesis and physiology. Thyroid stimulating hormone tsh, free thyroxine ft4, free triidothyronine ft3, thyroid antibodies. The term sick euthyroid is used in this condition since it represents a state of thyroid function appropriate for a sick individual. O confirmation of normal thyroid function o evaluation of thyroid hormone suppression and replacement therapy o detection of subclinical thyroid disease o detection of cases of inappropriate secretion of tsh thyroid hormone resistance, tsh secreting pituitary tumours tsh 0. Thyroid function tests american thyroid association. Interpretation of thyroid function tests may be particularly difficult if the patient is systemically ill. Classification of tests based on functions of thyroid tests measuring blood levels of thyroid hormones.
The assessment of thyroid function in newborns, especially premature infants, is challenging as are the interpretation of thyroid function tests in infancy through childhood. Interpretation of thyroid function tests the lancet. Changes in tsh can serve as an early warning system often occurring before the actual level of thyroid hormones in the body becomes too high or too low. Interpretation of thyroid function tests semantic scholar. However, there remain a few situations in which the results of tsh, free t4, and free t3 assays tend to point in different directions, as well as cases in whom thyroid. The thyroids job is to make thyroid hormones, which are secreted into the blood and then carried to every tissue in the body. Pregnancy and thyroid function in pregnancy, there is increased level of t4 and a corresponding decrease in tsh level. These lab tests represent all of the tests that are available for. This test is done to measure the level of thyroidstimulating hormone tsh in the blood which helps determine thyroid function.
Interpretation of thyroid function tests current medical. In ambulatory patients with intact hypothalamic and pituitary function, a normal tsh result excludes hypo or hyperthyroidism. Interpretation of laboratory thyroid function tests. Thyroid autoantibodies most acquired thyroid disorders are autoimmune thyroid peroxidase antibody tpo and anti thyroglobulin antibody tgab are associated with hashimoto thyroiditis. Thyroid function tests an overview sciencedirect topics. Lots of basic information about the thyroid gland can be found in the separate leaflet called thyroid and parathyroid glands. Pitfalls in the measurement and interpretation of thyroid function tests. Patients with a thyroid nodule or a multinodular goitre who have normal tfts may have thyroid cancer and must be referred to a specialist for further evaluation consideration of fna thyroid dysfunction in pregnancy postpartum mmt. The usual blood tests done for thyroid function are tsh, t4 and sometimes t3. There is a negative loglinear relationship between serum free t4 and tsh concentrations.
Nti or sick euthyroid syndrome is a relatively common finding following any acute or chronic illness, and is defined by the absence of. Low tsh and t 3 levels are typical and can cause diagnostic confusion. Overview of thyroid function endocrine and metabolic disorders. In these cases, interpretation of thyroid function tests is best done by an endocrinologist. American thyroid association thyroid function tests what is the thyroid gland. Tsh should be used as the firstline thyroid function test to assess thyroid hormone status. A high tsh level indicates that the thyroid gland is not making enough thyroid hormone.
Unfortunately, the currently used thyroid function test, based on a blood. Thyroid function tests are tests that can give information about how your thyroid is working. The thyroid gland is a butterflyshaped endocrine gland that is normally. Thyroid stimulating hormone testing is the preferred approach because. Understanding thyroid function tests and normal ranges. A common pitfall in the interpretation of thyroid function tests is to overlook the confounding effects of nonthyroidal illness nti. Thyroid function tests are used to establish the level of thyroid function e. Thyroid disorders, in which the gland produces too much or too little of the hormone, can influence many functions in your body, from your heart rate to your metabolism. Starvation or severe illness can be associated with dysregulation of tsh secretion and reduced deiodination of t 4 to t 3 the sick euthyroid syndrome. Thyroid disease is common, affecting approximately 1% of the female population, and there is a wide range of conditions affecting the thyroid gland, with a wide range of clinical features. Thyroid function tests are blood tests which help to check the function of your thyroid gland. That can sometimes be tricky, especially since one of the crucial measurements, thyroid stimulating hormone tsh, a brain hormone, moves in the opposite direction to most of the other compounds that are measured to assess thyroid function. Treating a thyroid hormone imbalance successfully requires interpreting thyroid test results correctly.
Interpretation of thyroid blood tests many doctors simplistically think that thyroid disease can be diagnosed, and even worse, can govern treatment, by testing only tsh levels. They are mainly used to detect an underactive thyroid gland hypothyroidism and an overactive thyroid gland hyperthyroidism. By comparing the values of thyroid tests, a doctor can determine whether a person has. Clinical examination a comprehensive collection of clinical examination osce guides that include stepbystep images of key steps, video demonstrations and pdf mark schemes. 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 overactive thyroid or hypothyroidism underactive thyroid, or to monitor the effectiveness of either thyroid suppression or hormone replacement therapy. Tsh thyroid function test normal values in children.
Thyroid function tests in pregnancy thyroid dysfunction affects 23% of pregnant women and overt maternal hypothyroidism is associated with adverse pregnancy outcomes. Thyroid function tests purpose, procedure health checkup. Nitin kapoor, mbbs, md,dm endo, abbm usa, post doc. Order tpo antibody only in the presence of goiter or. Thyroid and parathyroid disorders american family physician.
Test abbreviation typical ranges serum thyroxine t4 4. Interpreting thyroid function tests medical exam prep. Thyroid diseases are among the most prevalent of medical conditions. Jul 23, 20 thyroid tests assess inherent thyroid gland function radioactive iodine uptake test is used to assess intrinsic function of the thyroid gland this test is not specific and the reference range should be adjusted based on local population this test is indirect measure of thyroid activity 21. Nov 20, 2014 tsh first line test in thyroid function tests normal tsh level excludes thyroid dysfunction uses.
Nti or sick euthyroid syndrome is a relatively common finding following any acute or chronic illness, and is defined by the absence of an intrinsic abnormality of hpt function rather it is. A guide to thyroid function test interpretation tft interpretation, including the common tft patterns for hypothyroidism and hyperthyroidism. Jan 16, 2012 while t4 is the most widely used initial screening test for thyroid disorders, relying on this test alone is a primary reason for the misdiagnosis of canine and feline thyroid disorders. Thyroid function test normal values interpretation cost and. If your doctor thinks you are suffering from an overactive or underactive thyroid, she may order tests. A blood sample is taken from a vein in the arm and sent off to the laboratory for analysis. Thyroid disease frequently arises from autoimmune processes that stimulate overproduction of hormones hyperthyroidism or causes gland destruction that subsequently leads to underproduction of hormones hypothyroidism. A raised concentration of thyroid stimulating hormone with a low concentration of free thyroxine suggests hypothyroidism. Thyroid function tests tfts are amongst the most commonly requested laboratory investigations in both primary and secondary care. Hypothyroidism means that the thyroid gland cannot make enough thyroid hormone to keep. The introduction of sensitive thyrotropin assays and free thyroid hormone measurements has simplified the interpretation of thyroid function tests.
These hormones affect your temperature control and heart rate, and turn the food you eat into energy. Thyroid function test interpretation tft interpretation. Summary interpretation of thyroid function tests tfts is generally straightforward. Blood tests to measure tsh, t4, t3 and free t4 are readily available and. Tsh testing should not be used in the presence of nti, pituitary disease or tshsuppressing drugs. The most common thyroid function blood test measures the levels of thyroid stimulating hormone tsh, triiodothyronine t3 and thyroxine t4. Small changes in serum thyroid function cause logarithmic amplification in tsh secretion 3. Knowledge of this thyroid physiology is important in knowing what thyroid test or tests are needed to diagnose different diseases. Interpretation of thyroid function tests sciencedirect. Secretion of the thyroid hormones t4 thyroxine and t3 triiodothyronine is regulated by pituitary thyroidstimulating hormone tsh figure 1 and figure 2. The diagnosis and treatment of hypothyroidism seem. Understanding your thyroid function results your thyroid is a butterflyshaped gland in your neck.
Interpretation thyroid stimulating hormone tsh this test is used to identify primary hypothyroidism and to differentiate it from secondary pituitary and tertiary hypothalamus hypothyroidism. Cheapest test is to measure the total plasma levels of t3 and t4. Thyroid dysfunction can result in a wide range of symptoms and thyroid function tests tft are therefore one of the most common endocrine. Interference with tft interpretation due to committant drug therapy.
Principles of, and pitfalls in, thyroid function tests journal of. Amiodarone interferes both with the synthesis of tsh, with iodine uptake by the thyroid gland and with conversion of t4 to t3. However, in a minority of contexts the results of thyroid. This collection features the best content from afp, as identified by the afp editors, on thyroid and parathyroid disorders and related issues. While some conclusions can be drawn from a single test, a combination of test results are usually needed to establish the full nature of your thyroid health.
This page will be removed from your favorites links. Thyroid stimulating immunoglobulin tsi or tsh receptor antibody associated with graves disease. Aug 10, 2015 topic in focus interpretation of thyroid function tests cmi. Usually the free or active portion of t4 and t3 is measured i. Thyroid function test interpretation for antibodies the thyroid function test interpretation for these antibodies test helps to doctor to determine whether a goiter, hyperthyroidism, or hypothyroidism is a result of an autoimmune disorder. Screening for thyroid diseases especially those at high risk is cost effective as up to 20% of those with subclinical thyroid disease may turn to clinical thyroid disease timing and choosing the right thyroid test is the best approach in understanding the meaning of the results. Due to changes to thyroid physiology in pregnancy, pregnancy specific reference intervals are required to define thyroid conditions in pregnancy. The interpretation of thyroid function tests is a very popular exam topic. Topic in focus interpretation of thyroid function tests. When evaluating thyroid lab tests you want to check for more than just the tsh and look at other important thyroid functions such as peripheral thyroid conversion, immune function, and thyroid cellular sensitivity. Clinical examination a comprehensive collection of clinical examination osce guides that include stepbystep images of key steps, video demonstrations and pdf.
The thyroid gland is situated in the neck and produces two hormones thyroxine or t4 and triiodothyronine or t3. The thyroid gland is a butterflyshaped endocrine gland that is normally located in the lower front of the neck. Thyroid diseases are common and in most cases the interpretation of thyroid function tests is straightforward. Thyroid function tests what is a thyroid function test. How to test, interpret thyroid function veterinary practice. Pitfalls in the measurement and interpretation of thyroid.
Aug 03, 2015 thyroid dysfunction can result in a wide range of symptoms and thyroid function tests tft are therefore one of the most common endocrine tests ordered in general practice. Pdf version interpretation of thyroid function tests dr. These hormones act on cells in virtually every body tissue by combining with nuclear. The most common thyroid function blood test measures the levels of thyroidstimulating hormone tsh, triiodothyronine t3 and thyroxine t4. We propose that if assays for thyrotropin, free t3, and free t4 are all done, knowledge of these patterns coupled with clinical details and simple additional tests allow a diagnosis to be made in almost all cases. Jul 06, 2016 thyroid function tests purpose, procedure, normal values 5 min read july 6, 2016 the thyroid is an extremely important gland that is located in the neck and its main function is to produce thyroid hormones that are responsible for regulating various processes in the body such as metabolism, energy production and control of mood. What should be done when thyroid function tests do not make sense. Thyroid function tests are now readily available to, and widely used by. Thyroid disorders can be difficult to detect clinically, but thyroid function tests can assist in making a diagnosis. It may be impossible to interpret tfts in isolation and decisions may need to be taken on clinical grounds or on the pattern of change in tfts over a period of time. The best way to initially test thyroid function is to measure the tsh level in a blood sample. Thyroid function tests leeds teaching hospitals nhs trust. As a result, interpretation of thyroid function tests is now generally straightforward, and more than 90% of people investigated are diagnosed with normal thyroid gland function. However, important pitfalls and difficult cases still exist.
Illness has a significant impact on thyroid function tests and assessment in this group is described by drs. The most active thyroid hormone triiodothyronine, t3, is largely produced by peripheral ie nonthyroidal conversion of thyroxine, t4. No one single laboratory test is 100% accurate in diagnosing all types of thyroid disease. 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 overactive thyroid or hypothyroidism underactive thyroid, or to monitor the effectiveness of either thyroidsuppression or hormone replacement therapy. To help an individual interpret their thyroid lab tests and to recommend what thyroid labs they should have tested in the future. The thyroid gland secretes thyroxine t4 and triiodothyronine.