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      Decreased Levels of Ionized Calcium One Year after Hemithyroidectomy: Importance of Reduced Thyroid Hormones

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          Abstract

          Background: Previously we have found reduced levels of total serum calcium and 1,25(OH)<sub>2</sub>D<sub>3</sub> despite an unaltered stimulated parathyroid hormone (PTH) secretion 1 year after hemithyroidectomy. The present study was undertaken to elucidate the possible relationship between calcium homeostasis, thyroid hormones and bone resorption in a group of 45 consecutive patients subjected to hemithyroidectomy because of a solitary nodule. All patients had free T<sub>4</sub> and T<sub>3</sub> levels within normal range preoperatively. Methods: Thyroid hormones, bone mineral and biochemical variables known to reflect calcium homeostasis were studied. Patients were divided into three separate groups depending on their pre- and postoperative thyroid hormone status. Results: One year postoperatively, serum levels of free T<sub>4</sub> were decreased and that of thyrotropin (TSH) increased in the entire group of patients. The concentration of ionized calcium was reduced from 1.25 ± 0.05 to 1.22 ± 0.04 (p < 0.001) despite an unaltered PTH value (2.8 ± 1.0 vs. 3.1 ± 1.5, p = 0.50). A significant reduction in C-terminal telopeptide type 1 collagen (1CTP) indicated decreased bone resorption 1 year after surgery (p < 0.05). Subgroup analysis showed that a reduction in ionized calcium was seen only among patients with a postoperative decrease in free T<sub>4</sub>. Patients with subclinical hyperthyroidism preoperatively presented the lowest postoperative levels of ionized calcium, significantly reduced levels of 1CTP and increased levels of phosphate and creatinine. Multiple linear regression analysis showed that age (p < 0.05) and postoperatively changed serum levels of TSH (p < 0.05), creatinine (p < 0.05), phosphate (p < 0.001) and FT<sub>4</sub> (p < 0.01) were independently associated with altered levels of ionized calcium. Conclusion: We conclude that the reduction in ionized calcium 1 year after hemithyroidectomy was not due to PTH deficiency. Instead our results suggest that the reduced effects of thyroid hormones on bone and kidney function is essential.

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          Most cited references 3

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          Consistent reversible elevations of serum creatinine levels in severe hypothyroidism.

          Changes in routine clinical chemical indicators of renal function in the hypothyroid state are not well characterized, and are infrequently discussed in standard internal medicine or subspeciality textbooks. We evaluated 24 consecutive patients with iatrogenic hypothyroidism induced prior to radioiodine scanning for monitoring of thyroid carcinoma. Serum creatinine and thyroid function tests were measured prior to, during, and subsequent to the period of induced hypothyroidism. Among 29 episodes with paired prior euthyroid and hypothyroid serum creatinine values, the hypothyroid value was greater in 26 (89.7%), and equal in 3 (10.3%), less in none; the mean hypothyroid value was significantly greater (103 vs 76 micromol/L [1.17 vs 0.87 mg/dL]) (P<.001). Among 36 episodes with paired hypothyroid and subsequent euthyroid serum creatinine values, the hypothyroid value was greater in 33 (91.7%), equal in 2 (5.6%), and less in 1 (2.8%); the mean hypothyroid value was again significantly greater (102 vs 75 pmol/L [1.15 vs 0.85 mg/dL]) (P<.001). There was no significant difference between prior and subsequent euthyroid serum creatinine values. Serum creatinine values above the stated normal range occurred in 6 of 36 hypothyroid episodes. There is a consistent and reversible elevation of serum creatinine values in the hypothyroid state. Frankly abnormal serum creatinine levels will occur in some cases.
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            Effects of thyroid hormones on heart and kidney functions.

            Thyroid hormones affect the functions of several organs including the heart and kidney. Using isolated left papillary muscles we have investigated the action of thyroid hormones on the mechanical and electrical properties of the heart. We found that pure hypothyroidism causes a depression in contractile and electrical parameters, but we noticed that superimposed hypoparathyroidism accounts for the marked prolongation in contractile kinetics and action potential duration. At kidney level we have shown that thyroid hormones affect proximal tubular sodium transport and this effect is only partially mediated by the action of thyroid hormones on Na-K-ATPase activity. Using the micropuncture technique, we hypothesized that the early effect of thyroid hormone action is on the potassium permeability of proximal tubular cell membrane. This latter effect would explain the increase in isotonic fluid reabsorption through an increase in the driving force for sodium. Finally, hypothyroid patients have a decrease in glomerular filtration rate and renal plasma flow that are completely reversed by thyroxine administration. On the other hand, hyperthyroid subjects exhibit a significant increase in both parameters.
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              The Use of Oral Radiographic Contrast Agents in the Management of Hyperthyroidism

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                Author and article information

                Journal
                HRE
                Horm Res Paediatr
                10.1159/issn.1663-2818
                Hormone Research in Paediatrics
                S. Karger AG
                1663-2818
                1663-2826
                2001
                2001
                15 August 2001
                : 55
                : 2
                : 81-87
                Affiliations
                Departments of aSurgery and bInternal Medicine, Lund University Hospital, Lund, Sweden
                Article
                49975 Horm Res 2001;55:81–87
                10.1159/000049975
                11509864
                © 2001 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Tables: 4, References: 30, Pages: 7
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