Functional diagnosis of thyroid diseases

One of the leading places in the diagnosis of thyroid disease belongs to the method with the use of radioactive iodine.
This method allows to trace organic and inorganic phases of iodine metabolism, shape and location of the thyroid gland, to identify the tumor. The methods of determining inorganic phase of iodine exchange include: determination of the quantity of radioactive iodine (see) in the thyroid gland, allocated in the urine, thyroid clearance, determination of iodine in saliva, the ratio of the content of radioactive iodine in the thyroid to accumulation in the tissues (called the neck of the femur).
Methods defining hormone-secretory phase of iodine metabolism, are: the index of transformation, the percentage of radioactivity of erythrocytes and plasma and several others.
For practical purposes, adopted the method of determining the amount of radioactive iodine in the thyroid gland through 2.4 and 24 hours. The study is carried out either by contact method with application installation, B-2 (the tube Geiger - Muller put on the region of the thyroid gland) or using scintillation devices (then the measurement is carried out at 10-30 cm). Dose of input J131 does not exceed 1-5 mccoury that is harmless for the organism. Measurement at a distance of more accurately. Application of scintillation install SND-61 allows diagnosing not only disorder of the thyroid gland, and to approximately determine the location of the cancer, metastases and the degree of accumulation of radioactive iodine in the right and left parts.
The accumulation J131 in the thyroid gland 2 hours is the norm from 10 to 20% imposed iodine, 24 hours 30-50%; in patients with hyperthyroidism, these figures are significantly higher. In patients with myxedema they are 1-5%.
When eutireoidnyi goitre content of radioactive iodine in the thyroid gland in most cases does not exceed the norm; the same is observed and with thyroid cancer. Some patients may experience mismatch between rates of accumulation J131 in the thyroid gland and clinical picture of diffuse toxic goiter. Differences are observed more frequently in the evaluation indicators for the period of examination within 24 hours. On the results of the study due to the intake of iodine, as well as tireoidina, bromine, caffeine that suppress thyroid function and thereby reduce the absorption of its radioactive iodine.
More reliable test to detect hyperthyroidism is an indication of the rate of accumulation and allocation J131 thyroid gland for the first 2, 4, 6, 8, 12 and 24 hours.
Dynamics of accumulation of radioactive iodine in the thyroid depict graphically. The nature of the graphs is different in patients with different functional States glands (Fig. 9). In patients with thyrotoxicosis the accumulation of radioactive iodine is faster than healthy people and in patients with myxedema curve of accumulation almost never rises above the background.

Fig. 9. The accumulation of radioactive iodine in the thyroid gland in normal state and in case of various diseases.

Not less important method is the determination of the amount of radioactive iodine is excreted in the urine. In healthy people during the first days in the urine out 31-63% of the number of input radioactive iodine; in patients with hyperthyroidism 3-18%, hypothyroidism, and miksedeme 36 - 71%.
Diagnostic value is also the so-called iodine thyroid clearance that allows you to monitor the speed of the purification of the blood thyroid tissue from it contains radioactive iodine for a certain period of time. The amount of clearance is calculated from the ratio of the number J131 in the thyroid gland for a certain period of time the number of J131 1 ml of blood for the same length of time.
This attitude is in norm is 6 to 16 ml/min; in patients with hyperthyroidism 74-500 ml/min and in patients with myxedema 0-4 ml/min In malignant tumors figures vary depending on the degree of destruction of the thyroid gland. In addition to the thyroid clearance, enjoy renal clearance, representing the ratio of the number J131, excreted in the urine within 30 minutes, to the concentration J131 in the plasma during the same period.
Indicators renal clearance are not in full correlation with the state of the thyroid gland. May be inconsistencies, especially in patients with kidney disease, in which the number allocated J131 in urine falls at high concentrations in the thyroid gland.
To identify thyrotoxicosis in areas of endemic goiter is also used triyodtironina the suppression test, based on the property of triiodothyronine to suppress the fixation of radioactive iodine in the thyroid gland in healthy people and almost to restrict this activity in patients with thyrotoxicosis. When giving triiodothyronine healthy people (80-200 mcg within 8-12 days) decreased absorption J131 gland more than 20% in comparison with the data before taking this drug; in patients with hyperthyroidism occurs or a slight decrease absorption of radioactive iodine, or it even absent.
Of great importance in radioisotope diagnostics of thyroid pathology acquired method of determination of radioactive iodine in saliva (salivary test). When counting the number J131 3 cm3 saliva maximum its content is consistent in patients with thyrotoxicosis 83 pulses per 1 minute, in patients with hypothyroidism - to 24 000 pulses per 1 minute, in patients with normal thyroid function from 493 to 2393 pulses per 1 Tits. Exceptional accuracy has test "index relations", defining the attitude of radioactivity iodine saliva to radioactive iodine associated with the plasma protein. In patients with thyrotoxicosis indicator of this test is 0.14-44; hypothyroidism he reaches 338-3200, and in those with normal function of the glands varies from 150 to 250. This technique is more accurately shows the difference between Hypo - and hyperthyroidism. It allows you to way of distinguishing euthyroid state from hypothyroidism in patients who had previously tireostaticeski drugs.
For wide clinical and ambulatory examination of patients use a method based on a simplified study clearance. At the same time measure the content J131 in the thyroid gland and in the tissues of the hip ("attitude neck - femur"). The study was conducted in 1 to 2 hours after administration J131. The more radioactive iodine concentrates in the thyroid gland and less in the blood vessels of the thigh, the higher the activity of the thyroid gland. OK this ratio does not exceed 3; thyrotoxicosis ratio increases significantly, reaching 50-100; hypothyroidism is less than 3.
Research methods gormonalnozawisimae phase of iodine exchange include the definition of radioactive iodine associated with the plasma protein. OK (when defining 48 hours) in 1 liter of plasma contains 0,014-0,128% imposed dose J131, thyrotoxicosis is above 1%, hypothyroidism is within norm. The greatest value of this method is revealed in the diagnosis of thyrotoxicosis; he is often mistaken diagnosis of myxedema, arteriosa, as well as in the determination of residual signs of hyperthyroidism in patients previously treated with radioactive iodine.

A more accurate method is considered "index-conversion", i.e. determination of the degree of transformation of inorganic iodine in organic its shape. The index is determined from the relation (in the unit volume of plasma), multiplied by 100:
[J131associated with the plasma protein / J131 all plasma] X100.
Normally, the index is 13-42, thyrotoxicosis 45-96, hypothyroidism 2,7 is 12.5. This method is particularly recommended for the differential diagnosis of hypothyroidism from arteriosa.
Index of transformation of radioactive iodine in a protein-bound form can be defined also by the content J131 in erythrocytes and blood plasma on the basis of the relationship of radioactivity of erythrocytes to radioactivity in plasma. This ratio is in norm 0,46 with ray - an average of 0.25, hypothyroidism increased to 0.65. Radioactive iodine penetrate cells only in the inorganic form. Consequently, fewer inorganic iodine is contained in red blood cells, the more of the hormone in the blood plasma. The method is convenient because the antithyroid drugs not affect the study results. Also used method using labelled triiodothyronine, which allows to judge about the functional state of thyroid gland in vitro. Therefore, it can widely be applied to children, pregnant and lactating women, as well as with the blockade of the thyroid (iodine, antithyroid drugs).
In norm the inclusion labeled triiodothyronine in the red blood cell is from 10.5 to 20.8%, in patients with thyrotoxicosis from 22%to 43.6%, and in patients with hypothyroidism 4.5 to 11%.
Long half-life J131 does not allow repeated study of the thyroid gland earlier than in 5-6 weeks. Therefore, in practice is increasingly is using J132, which has a half-life of 2.4 hours. A short half-life reduces the radiation dose of the body almost in 100 times, and gonads - in 3-4 times.