  The thyroid gland The thyroid gland is a small butterfly-shaped gland at the base of the neck. It weighs only about 20 grams. However, the hormones it secretes are essential to all growth and metabolism. The gland is a regulator of all body functions. Thyroid disorders are found in 0.8-5% of the population and are 4 to 7 times more common in women.  Types of thyroid disease There are many types of thyroid disease. However, the main conditions present in most thyroid illnesses are hypothyroidism (thyroid under activity) and hyperthyroidism (thyroid over activity).

 The amino acid tyrosine is the starting point in the synthesis

 Thyroid hormones release

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 1.Radioactive iodine tests, testing uptake by the thyroid gland 2.Hormones concentration T3,T4 3.Thyroid Binding Globulin 4.Concentration of TSH 5.Urinary excretion of thyroid hormones 6.Tests influenced by the actions of thyroid hormones.(glucose tolerance test, calcium, cholestrol) 7.Thyroid antibody tests for cases autoimmune. The following are commonly used thyroid tests

  The main contribution of chemical measurements to the investigation of thyroid disease is to help sub- divide patients into the categories of effects of treatment. Tests for evaluate thyroid gland

  It must be emphasized that a single thyroid function test is not absolute in diagnostic accuracy and thus, a careful selection of tests, so that their combination can give comprehensive data, would enhance the diagnostic accuracy. Thyroid hormones

  Type of sample: blood, urine  Most blood tests involving hormones measure the bound protein. However, saliva-based testing measures the free level of hormone.  Conditions for test: you should ask the patient if he/she under treatment and receive drug or made surgery thyroidectomy recently.  Preparation the patient: be kind when you deal with patient.  You should read the diagnosis status on request. Sample collection

  Concentrations are usually lowered in thyroxicosis, due feedback inhibition of hypothalamus and pituitary  Conversely, plasma TSH is increased in hypothyroidism, except for the rare cases of hypothyroidism secondary to pituitary disease. TSH

 TSH is the most appropriate test when monitoring patients receiving thyroxine for the treatment of hypothyroidism. It should be measured no sooner than 6-8 weeks after the start of treatment. In the unusual situation where thyroid function needs to be assessed before this time, FT4 should be used, as the TSH will not have plateaued at this stage.

 TSH - In most situations TSH analysed using a high sensitivity assay is now accepted as the first line test for assessment of thyroid function. A TSH between 0.4 and 4.0 mIU/L gives 99% exclusion of hypo- or hyperthyroidism,12 while the TSH is considered more sensitive than FT4 to alterations of thyroid status in patients with primary thyroid disease. Thyroglobulin – Levels are increased in all types of thyrotoxicosis, except thyrotoxicosis factita caused by self-administration of thyroid hormone. The main role for thyroglobulin is in the follow-up of thyroid cancer patients. After total thyroidectomy and radioablation, thyroglobulin levels should be undetectable; measurable levels (>1 to 2ng/mL) suggest incomplete ablation or recurrent cancer.

  Thyrotropin (TSH)-secreting adenomas These rare tumors make too much thyroid-stimulating hormone (TSH), which then causes the thyroid gland to make too much thyroid hormone. This can cause symptoms of hyperthyroidism (overactive thyroid),

  Is more biologically active than T4 but both hormones have similar actions in the body.  T3 is not usually used in confirming the diagnosis of suspected hypothyroidism because other tests can demonstrate hypofunction of the thyroid gland.  Sometimes, however, a client may have clinical signs of thyrotoxicosis with a normal T4. Measurement of the T3 is then needed, because T3 may be elevated in thyrotoxicosis while other thyroid tests are still the normal range. T3

  FT3 - FT3 has little specificity or sensitivity for diagnosing hypothyroidism and adds little diagnostic information. The main value of FT3 is in the evaluation of the 2 to 5% of patients who are clinically hyperthyroid, but have normal FT4. In this situation, an elevated FT3 would be suggestive of T3 toxicosis, in which the thyroid secretes increased amount of T3 or there is excessive conversion of T4 to T3.

  The interpretation of results for serum T4 needs to take into account alterations in the thyroid-binding proteins.  The free thyroxine index (FTI) is determined by the following calculation:  FTI = Thyroxine (T4)/Thyroid Binding Capacity  The FTI is a normalized determination that remains relatively constant in healthy individuals and compensates for abnormal levels of binding proteins.  Hyperthyroidism causes increased FTI and hypothyroidism causes decreased value. T4

  FT4 - This test measures the metabolically active, unbound portion of T4. Measurement of FT4 eliminates the majority of protein binding errors associated with measurement of the outdated total T4, in particular the effects of oestrogen.

 FreeT4ng\dl{.8 – 2.2} TotalT4 Ug\ml{4.5 – 12.5} Free T3 Pg\ml{ } Total T3 ng\ml{.6 – 1.85} TSH MlU\ml{.5-5 } Parathyroid hormone(PTH) Pg\ml{9-52} Reference range

 There are marked variations in the thyroid function with age, evident in all of the vitro hormone and proteins measurements. In general thyroid function parameters in healthy subjects show little or no clinical significant gender or racial variation. Clinical interpretation

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  Quality control, the best step for all analytical tests to have a reliable result and a voiding the errors.  Pre analytical  Analytical process  Post analytical process Clinically errors

  A 63-year-old woman has Hashimoto’s disease. Her thyroid laboratory values today include the following: She feels consistently run down and has dry skin that does not respond to the use of hand creams. The hormones levels:  TSH 10.6 mIU/L (normal (0.5–4.5 mIU/L)  A free T4 concentration of 0.5 ng/dL (normal 0.8–1.9 ng/dL). Case study