How are Thyroid Disorders Diagnosed?
Blood Tests, Symptoms and Treatment of Thyroid Diseases
Aug 24, 2009
After the thyroid gland releases thyroid hormones into the blood, they are bound to plasma proteins called thyroxine-binding globulin (TBG), thyroid binding pre-albumin and albumin. T4 is bound more tightly than T3 so that although the concentration of total T4 in the blood is fifty times greater than that of T3, the free T4 is only three time that of free T3. It is likely that the only free hormone is available to the tissues of the body.
Blood Tests for Thyroid Disease
The function of the thyroid gland can be assessed by clinical examination but a lab test is needed to correctly diagnose a thyroid disorder as symptoms may not always be present. Hormone measurement is taken by measuring the level of TBG in the blood. The TBG level may be increased by such factors as pregnancy and the use of the birth control pill, can give a false positive diagnosis of hyperthyroidism (too much thyroid hormone produced). The opposite occurs when TBG levels are lowered by systemic illness such as diabetes. Genetic factors may also be responsible for higher or lower concentrations of TBG than normal.
Lab tests of Thyroid Stimulating Hormone (TSH) secreted by the pituitary gland in the brain are also used to measur thyroid function. A raised level of TSH in the blood usually indicates hypothyroidism (not enough thyroid hormone is being produced by the thyroid). TSH concentrations may also be raised transiently during recovery from illness or starvation and in rare cases in patients who have TSH secreting pituitary tumors.
If TSH concentration is lower than normal, this is usually due to hyperthyroidism or to excessively high doses of thyroxine replacement therapy given for the treatment of hypothyroidism.
Autoimmune Causes of Thyroid Disease
Tests to detect thyroid autoantibodies in the blood are used to find out the cause of a thyroid disorder. If the cause of hypothyroidism is autoimmune, meaning the body’s own immune system is destroying thyroid tissue, Thyroid microsomal antibodies or antioperoxidase antibodies will be found in most patients.
Disorders of Thyroid function
- Goiter: An enlargement of the thyroid gland is called a goiter and can cause either hypothyroidism or hyperthyroidism or not affect hormone levels at all.
- Graves disease is an autoimmune disorder which causes hyperthyroidism along with skin and eye symptoms.
- Hyperthyroidism affects the cardiovascular system because the thyroid hormones stimulate the heart, increasing heart rate and stroke volume. Weight loss commonly occurs inspite of an increase in appetite and effects on the nervous system lead to tremors, anxiety and general agitation. Prolonged hyperthyroidism may cause osteoporosis as well. Hyperthyroidism can be treated with antithyroid drugs, normally prescribed for up to two years. Surgical removal of thyroid tissue or its destruction by radioactive iodine are alternative methods of treatment.
- Hypothyroidism results when circulating levels of thyroid hormone are low. Hashimoto’s thyroiditis is the result of autoimmune damage to the thyroid gland. In atrophic hypothyroidism there is atrophy or shrinking of the gland, possible as a late consequence of autoimmune disease. Hypothyroidism may occur after thyroid surgery or radioactive iodine treatment and as a side-effect of certain drugs for example lithium. Pituitary or hypothalamic disorders may cause secondary hypothyroidism. Symptoms include tiredness, hair loss, hoarse voice, bradycardia, constipation, dry skin, weight gain, decreased appetite, carpal tunnel syndrome, menorrhagia infertility. Treatment of hypothyroidism involves the administration of thyroxine.
Thyroid Disorder in Infants
Congenital hypothyroidism in infants occurs in about 1/4000 births. It may result from a structural abnormality of the gland or more rarely from a defect in one of the enzymes involved in the production of thyroid hormones. If untreated, hypothyroidism in infants and toddlers leads to severe developmental delay, short stature and delayed puberty. In most developed countries all infants are screened for congenital hypothyroidism at the age of 5-7 days using a blood test. The sooner treatment with T4 is begun the better the prognosis with normal, healthy development in most children.
