1975, British Journal of Radiology, 48, 146-147
Technical note Mechanism of radioactive iodine uptake depression following intravenous urography By N. Coel, M.D.,* B. Talner, M.D.,tand H. Lang, Ph.D. School of Medicine and Department of Radiology, University Hospital of San Diego County, San Diego
ABSTRACT
TABLE I
The radioactive iodine (RAI) uptake examination is a standard test for the evaluation of thyroid diseases. For many years it has been known that the results of the RAI are depressed following administration of iodinated contrast media, such as that used for intravenous urography (Williams, 1968; Beierwates, 1956; Slingerland, 1957). The mechanism of this depression is not well documented. It is presumably due to inorganic iodide since it is only inorganic iodide that can be extracted from the blood by the thyroid gland. To study this problem we measured inorganic iodide in bottled contrast media.
INORGANIC IODIDE CONCENTRATION IN UROGRAPHIC CONTRAST MEDIA
METHOD
Four commonly-used urographic agents were assayed for inorganic iodide concentration. The agents tested were: sodium iothalamate (Conray400), sodium diatrizoate (Hypaque-50 per cent), meglumine iothalamate (Conray-60), and meglumine-sodium diatrizoate (Renografin-60). Different production lots were tested to avoid sampling errors. Trichloroacetic acid was added to the samples, followed by sodium nitrite to convert iodide to iodine (I2). The iodine was extracted into carbon tetrachloride, re-extracted in thiosulfate, and finally digested with chloric acid. This final sample was then titrated with thiosulfate using starch as the indicator. (A more detailed description of our method of iodide determination will be published (Lang et al., 1974.) RESULTS
The bottled contrast media had measurable inorganic iodide as high as 4-6 mg per 100 ml. (meglumine iothalamate). Table I shows the values for the different contrast media. DISCUSSION
Williams (1968) states that falsely low values for an RAI uptake will be obtained following administration of iodinated contrast media. The urographic, cholecystographic, angiographic, and myelographic contrast media are all organic compounds consisting of an iodinated benzene ring with various side chains. It is generally assumed that these compounds *USPHS Training Grant No. GM-02023 fSupported in part by USPHS General Research Support Grant No. RR-05665
Contrast material
Lot
Iodide (mg per 100 ml.)
Sodium diatrizoate (Hypaque-50 %) Meglumine-sodium diatrizoate (Renografin-60 %) Sodium iothalamate (Conray-400) Meglumine iothalamate (Conray-60)
A B
0-6 0-2
A B A B A B C
3-7,3-7 1-9,1-4 0-6,0-6 1-4,11 3-2,3-5 4-6 3-8
(Numbers separated by comma are values for different bottles within the same lot)
are stable while they are within the body and do not undergo de-iodination. It is inorganic iodide that is extracted and concentrated from the blood by the thyroid. For a routine intravenous urogram, between 50 and 100 ml. of water-soluble contrast media is injected. This gives the patient between 1 and 4 mg of inorganic iodide. As little as 1-2 mg of ingested iodide will depress thyroidal RAI uptake (Grayson, 1960; Stanley, 1949). At least this amount is given during urographic and cholecystographic examinations. In addition, we have demonstrated in vivo de-iodination of urographic contrast media in uremic patients (Talner, Coel, and Lang, 1973). It is likely that de-iodination of these compounds continues as long as they remain within the body, so that the uremic patient will split off more inorganic iodide than the patient with normal renal function. This time dependence may also explain the prolonged effect of myelographic contrast media left within the spinal canal on the RAI uptake. REFERENCES BEIERWATES, W. H., 1956. Value of radioactive iodine uptake and protein-bound iodine estimations in the diagnosis of thyrotoxicosis. Annals of Internal Medicine, 44,40-51.
146
FEBRUARY
1975
Technical note 131
GRAYSON, R. R., 1960. Factors influencing I thyroidal uptake. American Journal of Medicine, 28, 397-415.
thyroid hormone formation in man. The effect of the iodide ion on thyroid iodine utilization. Journal of Clinical
LANG, J., LASSER, E., TALNER, L., LYON, S., and COEL, M.,
Endocrinology & Metabolism, 9, 941-954.
1974. Inorganic iodide in contrast media. Investigative Radiology (in press). SLINGERLAND, D. W., 1957. Effects of an organic iodine compound (Priodax) on tests of thyroid function. Journal of Clinical Endocrinology, 17,82-93. STANLEY, M. M., 1949. The direct estimation of the rate of
TALNER, L. B., COAL, M. N., and LANG, J., 1973. Salivary secretion of iodine after urography: further evidence for in vivo deiodination and salivary secretion of contrast media. Radiology, 106, 263—268. WILLIAMS, R. H., 1968. Textbook of Endocrinology, pp. 163-164 (W. B. Saunders Co., Philadelphia).
147
Technical note Mechanism of radioactive iodine uptake depression following intravenous urography By N. Coel, M.D.,* B. Talner, M.D.,tand H. Lang, Ph.D. School of Medicine and Department of Radiology, University Hospital of San Diego County, San Diego
ABSTRACT
TABLE I
The radioactive iodine (RAI) uptake examination is a standard test for the evaluation of thyroid diseases. For many years it has been known that the results of the RAI are depressed following administration of iodinated contrast media, such as that used for intravenous urography (Williams, 1968; Beierwates, 1956; Slingerland, 1957). The mechanism of this depression is not well documented. It is presumably due to inorganic iodide since it is only inorganic iodide that can be extracted from the blood by the thyroid gland. To study this problem we measured inorganic iodide in bottled contrast media.
INORGANIC IODIDE CONCENTRATION IN UROGRAPHIC CONTRAST MEDIA
METHOD
Four commonly-used urographic agents were assayed for inorganic iodide concentration. The agents tested were: sodium iothalamate (Conray400), sodium diatrizoate (Hypaque-50 per cent), meglumine iothalamate (Conray-60), and meglumine-sodium diatrizoate (Renografin-60). Different production lots were tested to avoid sampling errors. Trichloroacetic acid was added to the samples, followed by sodium nitrite to convert iodide to iodine (I2). The iodine was extracted into carbon tetrachloride, re-extracted in thiosulfate, and finally digested with chloric acid. This final sample was then titrated with thiosulfate using starch as the indicator. (A more detailed description of our method of iodide determination will be published (Lang et al., 1974.) RESULTS
The bottled contrast media had measurable inorganic iodide as high as 4-6 mg per 100 ml. (meglumine iothalamate). Table I shows the values for the different contrast media. DISCUSSION
Williams (1968) states that falsely low values for an RAI uptake will be obtained following administration of iodinated contrast media. The urographic, cholecystographic, angiographic, and myelographic contrast media are all organic compounds consisting of an iodinated benzene ring with various side chains. It is generally assumed that these compounds *USPHS Training Grant No. GM-02023 fSupported in part by USPHS General Research Support Grant No. RR-05665
Contrast material
Lot
Iodide (mg per 100 ml.)
Sodium diatrizoate (Hypaque-50 %) Meglumine-sodium diatrizoate (Renografin-60 %) Sodium iothalamate (Conray-400) Meglumine iothalamate (Conray-60)
A B
0-6 0-2
A B A B A B C
3-7,3-7 1-9,1-4 0-6,0-6 1-4,11 3-2,3-5 4-6 3-8
(Numbers separated by comma are values for different bottles within the same lot)
are stable while they are within the body and do not undergo de-iodination. It is inorganic iodide that is extracted and concentrated from the blood by the thyroid. For a routine intravenous urogram, between 50 and 100 ml. of water-soluble contrast media is injected. This gives the patient between 1 and 4 mg of inorganic iodide. As little as 1-2 mg of ingested iodide will depress thyroidal RAI uptake (Grayson, 1960; Stanley, 1949). At least this amount is given during urographic and cholecystographic examinations. In addition, we have demonstrated in vivo de-iodination of urographic contrast media in uremic patients (Talner, Coel, and Lang, 1973). It is likely that de-iodination of these compounds continues as long as they remain within the body, so that the uremic patient will split off more inorganic iodide than the patient with normal renal function. This time dependence may also explain the prolonged effect of myelographic contrast media left within the spinal canal on the RAI uptake. REFERENCES BEIERWATES, W. H., 1956. Value of radioactive iodine uptake and protein-bound iodine estimations in the diagnosis of thyrotoxicosis. Annals of Internal Medicine, 44,40-51.
146
FEBRUARY
1975
Technical note 131
GRAYSON, R. R., 1960. Factors influencing I thyroidal uptake. American Journal of Medicine, 28, 397-415.
thyroid hormone formation in man. The effect of the iodide ion on thyroid iodine utilization. Journal of Clinical
LANG, J., LASSER, E., TALNER, L., LYON, S., and COEL, M.,
Endocrinology & Metabolism, 9, 941-954.
1974. Inorganic iodide in contrast media. Investigative Radiology (in press). SLINGERLAND, D. W., 1957. Effects of an organic iodine compound (Priodax) on tests of thyroid function. Journal of Clinical Endocrinology, 17,82-93. STANLEY, M. M., 1949. The direct estimation of the rate of
TALNER, L. B., COAL, M. N., and LANG, J., 1973. Salivary secretion of iodine after urography: further evidence for in vivo deiodination and salivary secretion of contrast media. Radiology, 106, 263—268. WILLIAMS, R. H., 1968. Textbook of Endocrinology, pp. 163-164 (W. B. Saunders Co., Philadelphia).
147
