Thyroid Iodine Uptake PDF

THE FUNCTIONAL INVESTIGATION OF THE THYROID THYROID IODINE UPTAKE The radioactive iodine uptake (RAIU) test uses a radioactive tracer to quantify how much tracer the thyroid gland absorbs from the blood. The test can show how much tracer is uptaken by the 131 thyroid gland....

THE FUNCTIONAL INVESTIGATION OF THE THYROID THYROID IODINE UPTAKE The radioactive iodine uptake (RAIU) test uses a radioactive tracer to quantify how much tracer the thyroid gland absorbs from the blood. The test can show how much tracer is uptaken by the 131 thyroid gland. I is administrated orally, and the measurements (dosimetry readings) are done at 4 and 24 hours, using a gamma scintillation counter. Conditions to perform a reliable test: the patient is not allowed to eat for 2 hours before the test and to take any antithyroid medicine for 5 to 7 days before the test. The radioactive tracer (11 µCu (microCurrie) is given orally or intravenous. The percentage of thyroidal radioactive iodide uptake (RAIU) is calculated from the counts cumulated per constant time unit, at 2 and 24 hours. The percentage of RAIU 24 hours after the administration of radioiodide is most useful. Normal values for 24-hour RAIU are 5 to 30 percent. Lower normal values are due to the increase in dietary iodine intake following the enrichment of foods, particularly mass produced bread (150 µg of iodine per slice), with this element. The intake of large amounts of iodide (>5 mg/day), mainly from the use of iodine-containing radiologic contrast media, antiseptics, vitamins, and drugs such as amiodarone, suppresses the RAIU values to a level hardly detectable using the usual equipment and doses of the isotope. Depending upon the type of iodine preparation and the period of exposure, depression of RAIU can last for weeks, months, or even years. Even external application of iodide may suppress thyroidal radioiodide uptake. The need to inquire about individual dietary habits and sources of excess iodide intake is obvious. The test does not measure hormone production and release but the avidity of the thyroid gland for iodide and its rate of clearance relative to the kidney. Disease states resulting in excessive production and release of thyroid hormone are most often associated with increased thyroidal RAIU and those causing hormone underproduction with decreased thyroidal RAIU. High or low thyroidal RAIU as a result of low or high dietary iodine intake, respectively, may not be associated with significant changes in thyroid hormone secretion. Examples of thyroidal RAIU curves under various pathological conditions. Note the prolonged uptake in renal disease due to decreased urinary excretion of the isotope and the early decline in thyroidal radioiodide content in some patients with thyrotoxicosis associated with a small but rapidly turning over intrathyroidal iodine pool. Normal range: ~5-30% Increased RAIU Graves Disease Toxic Multinodular Goiter Thyroid Adenoma Decreased RAIU Subacute or Silent Thyroiditis Iodine-Induced THE BASAL METABOLIC RATE (BMR) The basal metabolic rate represents the minimal amount of energy neccesary for the basic vital processes maintenance (respiration, circulation). The principle of determination is represented by the direct relationship between the body oxygen consumption and the amount of heat produced in organism in a given interval of time. For the accurate determination of the BMR , a set of conditions should be accomplished: 1. Rest conditions, avoinding any physical or intelectual effort,: it is also necessary to avoid an intense physical effort 1-2 days before determination, because the biochemical changes associated with physical effort can last few days and can increase the value of BMR. 2. Starvation for 12 hours beforre determination and avoiding of proteins; these nutrients have a special property to release a supplimenatry amount of heat during their metabolization (dynamic specifica activity of proteins). 3. Confort temperature, to avoid the supplimentary expense of energy for termoregulation; an optimal temperature is between 20-22ºC for the dressed subject and 24-26 22ºC for the undressed ones. 4. Avoiding of any emotions, stress, tension, a special relaxing room with walls painted in nonstressfull colours (green, light blue). Steps in BMR determination Body oxygen consumption determination can be measured with Benedict spirometer, which uses a closed system. It consists in a cylinder filled with pure oxygen, immersed at its base in water. The subjects breath pure oxygen from the spirometer for 6 minutes. During this interval, the respiratory movements and their amplitude can be recorded. The expiratory air turns back into the spirometer, so the oxygen isn’t lost. CO2 and water vapors are uptaken by a special substance (sodium carbonate), so the system contains only oxygen. Due to the oxygen consumption, as ascendent slope is recorded , in 6 minutes, by the apparate. The height of this slope is noted with „h”. The determination of the volume of oxygen consumed in 6 min. We use for this determination: O2 caloric coeficient – the amount of energy (in kilocalories) released by 1liter of oxygen, when are metabolised sugars (5,04 cal), proteins (4,48 cal), lipids (4,68 cal);  winch spirogram Pure oxygen water Benedict spirometer The patient inhales pure oxygen from the spirograph cylinder and exhales in the same tube; water vapors and carbon dioxide are removed by a special substance, so in the cylinder will remain only the pure oxyge. As much as oxygen is consumed, the cylinder goes done but the winch, the arrow will draw an ascending slope. The heigh of the graphic = h. h 6 min. Respiratory graph for BMR calculation The subject is connected to apparate and breath pure oxygen for 6 minutes. The recording system shows an ascending graphis, similar to a spirogram. To calculate the oxygen volume consumed in 6 minutes, we have to multiply the h to cylinder surface = 2,85 dm2. VO2 /6 min = 2,85 (dm2) x h (dm) = n dm3 = n liters of oxyge. To calculate oxygen consumption per 24c hours, we have to multiply „n” to 10 and to 24, so: VO2 /24 hours = n x 10 x 24 = liter/24 hours. To calculate the energy consumption, we have to multiply the VO2 /24 hours to oxygen isocaloric coeficient, an average between caloric coeficient of sugars, lipids and proteins , because human food is a balanced one and contain all types of nutrients. The isocaloric coeficient = 4,85 Kcal/l O2 Then energy consumption/24 h = VO2 /24 hours (l) x 4,85 Kcal/l O2. Energy consumption/24 h The BMR = body surface( m2) The obtained result represents the calculated (real) value of BMR in a given person. To interpretate this value, we have to compare it with the standard (theorethical) value of BMR, obtained from tables ( Harris Benedict tables). The theorethical BMR …………………….100% The calculated BMR…………………………..x ΔBMR = 100% + x% = + 10%. The % difference (ΔBMR) between the theorethical BMR and the calculated BMR is normal + 10%. An increased ΔBMR is associated with hyperthyroidism and the decreased ΔBMR with hypothyroidism. THE ORAL GLUCOSE TOLERANCE TEST - OGTT (or provoked hyperglycemia test) consists of the oral administration of a standard amount of glucose followed by blood samples drawning at each hour, for 2 hours. The test appreciates the insulinic response against glucose overload. WHO (World Health Organization) recommended a methodology and interpretation procedure as follows: 3 days before OGTT, patient should follow a standard diet with 150 g sugars, with fats and proteins. The patient should have been fasting for the previous 8-14 hours. Test starts with the drawning of a zero time (baseline) blood sample. The patient is given a glucose solution to drink (pure glucose powder dissolved in water or tea). The standard dose since the late 1970s has been 1.75 grams of glucose / kg of body weight, to a maximum dose of 75 g. It should be drunk within 5 minutes. Prior to 1975 a dose of 100 g was often used. Blood samples are drawn at intervals for measurement of glucose (blood sugar), and insulin levels if neccessary. The intervals and number of samples vary according to the purpose of the test. For simple diabetes screening, the most important sample is the 2 hour sample and the 0 and 2 hour samples may be the only ones collected. INTERPRETATION Glycemia à jeun (uneaten) in normals is bellow 100 mg /dl; A tone hour after glucose ingestion, glycemia increases less then 140 mg/dl in normals; Then decreases, turning back to rest value after 2 hours. The graphic representation consists in two parts: the ascendent slope corresponds with already synthesized insulin release; the second one, descendent slope corresponds with new synthesized and secreted insulin. The abnormalities of one or both of these moments are related with diabetes mellitus risk. If the 1 hour value of glycemia excedes 140 mg/dl, it reflects abnormalities in insulin secretion. If at 2 hour value exceedes 120 mg/dl, it reflects abnormalities in synthesis. A positive OGTT test strongly suggest diabetes mellitus. This is a heterogenous clinical syndrome in which the central feature is a chronic elevation of the blood glucose concentration - this results in a range of pathologies, due to a deficiency of insulin (absolute) or a resistance to insulin (relative). The chronic hyperglycemia is associated with long term tissue damage, especially the blood vessels, nerves, heart, kidneys and eyes. There are two types of diabetes: Type 1 diabetes mellitus appears classically in younger age groups, the onset is acute and insulin is needed for survival - generally present with a history of polyuria, polydipsia, lethargy and weight loss over a period of up to two weeks - many may present with ketoacidosis. In older age groups onset is more insidious - residual beta cell function lessens risk of ketoacidosis at time of presentation. Type2 diabetes mellitus usually occurs in older age groups - especially obese (in 70%) (however, incidence in child is assumed to be increasing due to increased prevalence of childhood obesity). 50% have hypertension and classical signs of thirst, polyuria, nocturia and weight loss are not always present. Often starts with fatigue and malaise.