Thyroid Test Investigation and Interpretation
Posted By HealthcareOnTime Team
Posted on 2021-06-24
Never Overlook Thyroid. Neha was frustrated. She always had trouble keeping a normal weight. She became so fatigue, she could not shed the extra weight put on during the pregnancy and exercising seemed impossible to her. Her face broke out in acne due to dry and oily skin. Sometimes she underwent higher incidences of depression and mood fluctuations. On the top of that, without analyzing the cause her primary care doctor put her on anti-depressants. Such uninvestigated thyroid problems can dramatically increase the risk. There are many alike cases where the proximate cause 'thyroid' is ignored due to wide ranging and non specific symptoms. Thyroid can affect every aspect of your health. Therefore, do not ignore this master endocrine gland.
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Being a ductless gland its hormones are secreted directly into the bloodstream. Triiodothyronine (T3) and thyroxine (T4), the two thyroid hormones are the sparks of life. They keep the body active physically as well as mentally, maintain body temperature and energy levels, fluid balance, cardiac rate when produced normally. But their production is not possible without stimulation from pituitary gland's thyroid stimulating hormone (TSH) which in turn is also regulated by the hypothalamus secreted TSH Releasing Hormone (TRH). In circulation when T3 and T4 are at sufficient level they exert negative feedback effect on TRH and TSH secretion. This production and control system ensures secretion of right amount of T3 and T4, but it can go wrong signaling the potential health issues. Circumstantially, it becomes essential to have laboratory investigations to rule out any possibilities of thyroid abnormality.
Thyroid Lab Tests Thyroid function tests are amongst the most commonly requested laboratory tests performed by sensitive, simple and accurate immunoassay technique that combines chemistry and immunology to detect specific analyte. The thyroid tests conducted in laboratory are: Measurement of TSH TSH is often the test of choice to investigate overactive or under performing thyroid also called hyperthyroidism or hypothyroidism. The normal reference range for TSH is approximately 0.5 to 5.5 ulU/ml. TSH levels less than 0.5 are considered possible evidence of hyperthyroidism or too much production of T3 and T4 whereas above 5.0 (elevated TSH) indicate hypothyroidism or inadequate response of thyroid gland to the stimulation of TSH. However, there is an ongoing dispute among thyroid experts that the range should be narrowed. American Association of Endocrinologists has revised the normal range to 0.3 to 3.0 wIU/ml. TSH levels differ with the abnormality such as in thyrotoxicosis, suppression of TSH by T4 below the normal range is seen. Conversely, TSH levels are raised above the normal range in hypothyroidism. Diagnosis becomes difficult in asymptomatic cases like subclinical hypothyroidism necessitating blood test to detect the disorder. Apart from this, pituitary failure can also hamper TSH production. Also there are times when fluctuations in TSH levels are observed within small time frame.
TSH Fluctuations Many commonly observed reasons produce marked difference in TSH values within a short time span that includes dosage of medications, high fiber diet, calcium/iron supplements, consumption of goitrogenic food (soy product, cauliflower, cabbage, raddish, etc.), stress and seasonal changes. Set of patients complain of their TSH levels having drastically fluctuated from a value as low as 3 to a test value of 11 over a period of just three months. Also there are cases wherein TSH values have been steeply declined. Such deviations in TSH levels become a matter of high concern to the patients and consequentially have to be dealt with immense concern by the laboratory since it becomes their responsibility to make the patients aware of the fact that TSH is one parameter that is susceptible to extreme fluctuations and there are a list of factors and issues that easily cause such drastic deviations, which might appear erroneous to a person who is not aware of the sensitive nature of this hormone which is prone to least stability. Considering all in all, if TSH levels are abnormal, far clear picture of thyroid is needed which can be obtained by testing T3 and T4 levels.
T4 and T3 Thyroid Test Measurement of thyroid hormones T4 and T3 is necessary only when the TSH levels falls outside the normal limits. Generally, these thyroid hormones are bound to the protein molecules or carrier proteins like thyroxine binding globulin (TBG), transthyretin or albumin. In the bound state, thyroid hormones are not available to the body's cells. However some amount of hormone exists in free state (FT4 and FT3) which represents the true thyroid hormone pool of the body. Unlike total T4 or T3 blood test, FT4 and FT3 test are not affected by protein levels and therefore provides more reliable measurement of hormones in the body. In clinical practice, the impetus to develop free hormone test is high since the concentration of TBG changes during pregnancy, infections, drugs or some severe systemic illness. In Graves disease and solitary toxic nodule, quite marked rise in hormone levels is observed while marginal hike is observed in patients with multinodular goiter (Plummer's disease).
Thyroid Antibodies The test for thyroid antibodies is advised by physician when thyroid is suspected to be in the process of autoimmune failure. The protein involved in production of thyroid hormones is thyroglobulin and detection of anti-thyroglobulin antibodies may be observed in case of thyroid cancer. Similarly, the antibody responsible for development of Grave's disease are anti-TSH antibodies and those for Hashimoto's thyroiditis (hypothyroidism) are anti-thyroid peroxidase (anti-TPO) produced against an enzyme, thyroid peroxidase located in the mitochondria of thyroid cells. Mild to moderately elevated levels of thyroid antibodies may be found in cases like thyroid cancer, type 1 diabetes, rheumatoid arthritis and pernicious anemia. However, significantly increased concentrations indicate thyroid autoimmune disorders such as Hashimotos's thyroiditis and Grave's disease.
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Thyroid Tumor Markers Thyroglobulin (Tg) - This thyroid protein is an invaluable diagnostic tool especially in monitoring thyroid cancer. The power of Tg measurement is that Tg can only be produced by thyroid gland. This means, when thyroid gland is completely removed in an individual, the Tg levels should theoretically be zero. So the measurement of Tg in blood can be used as an effective biochemical marker to detect if any cancerous tissue is left behind and also to detect metastasis. Thus, following definitive treatment for thyroid cancer Tg levels are monitored on regular basis. Levels greater than 5 ng/ml are suggestive of residual disease which can be treated with radioiodine (131 I) or external beam radiotherapy.
Calcitonin-it is a hormone produces only by the cells of thyroid gland . It provides a unique marker for monitoring patients who have undergone total thyroidectomy for medullary thyroid cancer . Following thyroid surgery when calcitonin levels are persitently raised reccurent medulary thyroid cancer is suspected and further surgery or radiotherapy may be contemplated .
Further Investigations Apart from these immunoassay techniques, radioisotopes are accustomed for thyroid investigations, especially thyroid cancer. The procedures such as FNAC, ultrasound, radioisotope scanning, CT and MRI scanning are implemented for assessing thyroid nodules, residual, recurrent or metastatic tumors.
Undoubtedly, thyroid diseases are complex but laboratory investigations and its interpretation are even dodgy.
For definite diagnosis of the suspected thyroid disorder along with laboratory investigations concise and detailed history of the patient and physical examination is essential. Since no one single laboratory test is 100% accurate in diagnosing all types of thyroid disorders. However, combination of two or more tests usually helps to detect the exact cause of thyroid abnormality.