Radioactive iodine uptake test

Physiologic Function Testing, An example of this application is the assay of thyroid hormone levels in (lie blood winch, in turn, can aid in the assessment of thyroid function. The radioactive iodine uptake test, which involves the administration of a dose of l31l (iodine-131) to the patient, is also a valuable procedure in assessing thyroid function. At present, the technique is best reserved for problem cases rather than used as a primary screening test. The main disadvantage of this test is the effect of the dietary intake of iodine, which reacts in various ways in different individuals. 

Radioactive iodine uptake test. Lower than normal neck uptakes suggest hypothyroidism. This can followed by ... 

In cases of lymphocytic thyroiditis with hyperthyroidism however, uptake and hormone secretion functions are uncoupled. Uptake function is blocked, but hormonal secretion proceeds. In these cases radioactive iodine uptake tests are not valid. Repeated measurements of total thyroid iodine by XRF can however give an estimate of the rate of decline of the iodine pool and this indirectly allows an... 

E.T. Wong and A.C. Schultz, Changing Values for the Normal Thyroid Radioactive Iodine Uptake Test, JAMA 238 1741-3 (1977). 

Physical examination revealed blood pressure 180/90 mm Hg, heart rate 110/min, minimal proptosis, and an enlarged thyroid gland. Laboratory tests showed elevated thyroxine, resin uptake, radioactive iodine uptake, and antimicrosomal antibodies. A diagnosis of hyperimmune hyperthyroidism (Graves disease) was made. 

Many "normal" persons in industrialized countries have various thyroid function tests measured as part of routine laboratory assessment. Iodine deficiency is associated with increased values for radioactive iodine uptake and serum TSH, thyroglobulin, and T3, and a decreased value for serum T4. Collecting data from normal subjects, representative of the population at large, as they undergo these tests can provide a general impression of the adequacy of iodine intake. Ultrasound is now widely used in physician s offices in Europe, and measurement of the thyroid size of normals provides a valuable marker for the amount of iodine in the diet. 

Radioactive iodine uptake (24 values) reach the 40 % in normal adults, but the normal ranges of other thyroid function tests (T, T, TSH etc) do not differ significantly from the international standards in neonates, children and adults. The incidence of congenital hypothyroidism (CH) detected by... 

When the uptake of a standard dose of radio-iodine is tested at the end of the treatment period, the radioactivity found in the thyroid gland is used as the parameter instead of the iodine content. 

A considerable advance in the management of thyroid cancer has resulted from the introduction of recombinant human TSH (thyrogen). A dose of 0.9 mg is administered intramuscularly, followed by an identical dose 24 hours later. The serum thyroglobuLin is then measured 48-72 hours after the second TSH injection this has become the preferred diagnostic test for following patients with differentiated thyroid cancer who have had thyroidectomy and ablation of any remnant tissue with radioactive iodine. This regimen can also be used to stimulate iodine uptake by malignant cells in a total body scan (see below). 

As part of the biogeochemical cycle, the injection of iodine-containing gases into the atmosphere, and their subsequent chemical transformation therein, play a crucial role in environmental and health aspects associated with iodine - most importandy, in determining the quantity of the element available to the mammalian diet. This chapter focuses on these processes and the variety of gas- and aerosol-phase species that constitute the terrestrial iodine cycle, through discussion of the origin and measurement of atmospheric iodine in its various forms ( Sources and Measurements of Atmospheric Iodine ), the principal photo-chemical pathways in the gas phase ( Photolysis and Gas-Phase Iodine Chemistry ), and the role of aerosol uptake and chemistry and new particle production ( Aerosol Chemistry and Particle Formation ). Potential health and environmental issues related to atmospheric iodine are also reviewed ( Health and Environment Impacts ), along with discussion of the consequences of the release of radioactive iodine (1-131) into the air from nuclear reactor accidents and weapons tests that have occurred over the past half-century or so ( Radioactive Iodine Atmospheric Sources and Consequences ). 

Measurement of the thyroid uptake of radioactive iodine has for many years been a useful supplement to thyroid function tests on blood. While thyroid uptake tests are not usually part of the services oflFered by a clinical chemistry department, they should always be considered in relation to the clinical chemistry tests, and therefore a brief discussion on them is relevant in this review. 

The result of the radioactive iodine neck uptake test may be high. 

TSH stimulation test. This involves injecting TSH and measuring the radioactive iodine neck uptake the following day. Lack of any increase in uptake is usually indicative of primary hypothyroidism. Some response usually occurs in secondary hypothyroidism. 

An in vivo test for the diagnosis of thyroid disorders which consists of giving radioactive iodine to the patient and measuring its uptake by the thyroid gland, by means of a radioactive counter placed over the gland. Uptakes are usually measured after 4 or 24 hours. High uptakes occur in hyperthyroidism whereas low uptakes are found in hypothyroidism. 

Radioactively labelled technetium ( " Tc) can be used instead of radioactive iodine (see radioactive iodine neck uptake test) for the assessment of thyroid gland activity. Its half life is six hours and thus the radiation dose to the patient is less than that given... 

Radioactive iodine neck uptake test. High uptakes suggest hyperthyroidism low uptakes suggest hypothyroidism. This test may be followed by a TSH stimulation test or a T3 suppression test. 

A test used in the differential diagnosis of hypothyroidism when a low radioactive iodine neck uptake has been found. TSH is given to the patient daily and the neck uptake test is repeated. This should result in an increased uptake in normal individuals. No response occurs in primary hypothyroidism. If the hypothyroidism is secondary to pituitary dysfunction, the increase in uptake to normal values may take several days. 

See also radioactive iodine neck uptake test T3 SUPPRESSION TEST... 

A high radioactive iodine neck uptake test (q.v.) is usually indicative of hyperthyroidism, although a high uptake can occur if the patient is iodine deficient or is taking anti-thyroid drugs. The neck uptake test can therefore be repeated after triiodothyronine (T3) administration. This normally suppresses TSH secretion, resulting in a low uptake. However, in hyperthyroidism but not in the other conditions listed above, no such suppression occurs. 

Radiation injury—People who are deficient in iodine are more susceptible to damage to their thyroid glands by radioactive iodine (1-131), an atmospheric contaminant which results from the testing of nuclear weapons. The reason to the increased susceptibility is that iodine deficiency causes the thyroid gland to increase the rate of its uptake of both normal and radioactive iodine. 

V Grayson R.R. I960 Factors which influence the radioactive iodine thyroidal uptake test. Am.J.Med.,... 

Although it provides a very obvious field for investigation, a possible relationship between bromine and iodine metabolism has attracted very few workers. In fact, it is not even definitely established that the normal thyroid contains more bromine than any other tisuse in the body. Perlman and associates studied the distribution of administered radioactive bromine and concluded from their data that the thyroid showed a greater uptake of the labeled bromine than any of the other tissues tested and that this uptake could not be explained on the basis of simple diffusion from... 

This is a test of thyroid function by using a radioactive isotope of iodine, 1. After administering the test dose, the uptake and utilization of iodine by the thyroid gland is measured by tracing the I . ... 

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