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      Isotopic Renal Function Studies in Severe Hypothyroidism and after Thyroid Hormone Replacement Therapy

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          Aim: To investigate the possible changes in the renal tubular function in severe short-term hypothyroidism using <sup>99m</sup>Tc-MAG<sub>3</sub> renography. Methods: 27 consecutive thyroidectomized patients (7 males and 20 females) aged 19–79 (mean 53) years were included in the present study. <sup>99m</sup>Tc-MAG<sub>3</sub> renography was performed in all patients before and after thyroid hormone replacement therapy. In addition, <sup>51</sup>Cr-EDTA clearance and serum creatinine concentrations were determined. Results: The serum creatinine concentrations were significantly increased in hypothyroidism as compared with the concentrations after thyroxine substitution (1.30 ± 0.44 vs. 1.04 ± 0.32 mg/dl, p < 0.05). According to the <sup>51</sup>Cr-EDTA clearance, the glomerular filtration rate was significantly lower in hypothyroidism than after treatment (61 ± 18 vs. 75 ± 23 ml/min). In contrast, we did not find any significant change in the renographic parameters for <sup>99m</sup>Tc-MAG<sub>3</sub> before and after treatment (total excreted activity 20 min after administration 51 ± 12 vs. 54 ± 14%; T<sub>max</sub> left:right 4.2 ± 1.77 : 3.91 ± 1.06 min vs. 4.1 ± 1.66 : 4.4 ± 1.96 min). Conclusions: We did not find any influence of thyroid hormones on the outcome of <sup>99m </sup>Tc-MAG<sub>3</sub> renography. As <sup>99m</sup>Tc-MAG<sub>3</sub> reflects the tubular function, it seems that the renal hemodynamic changes in severe hypothyroidism mainly affect the glomerular function. In general, the glomerular filtration rate reduction seems to be reversible after hormone substitution therapy; however, care has to be taken in patients with renal insufficiency.

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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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            Blood volumes and renal function in overt and subclinical primary hypothyroidism.

            Thyroid dysfunction is associated with marked alterations in cardiovascular and renal functions. In hypothyroidism, myocardial contractility, cardiac output, and oxygen consumption are decreased, whereas peripheral resistance is increased. We assessed blood volumes and effective renal plasma blood flow (ERPF) and glomerular filtration rate (GFR) in 17 patients with overt primary hypothyroidism and in 15 of these patients when in euthyroid state after substitutive therapy. We performed the same measurements in eight patients with subclinical hypothyroidism. In the hypothyroid state, the plasma volume measured by dilution of 125I-albumin (APV) was higher than the calculated plasma volume (CPV) from packed red cell mass, suggesting an extravascular escape of albumin. After substitutive therapy, the CPV showed a statistical increase (P < 0.05), whereas APV remained unchanged. Both ERPF and GFR increased after thyroxine therapy (p < 0.05). In the subclinical group, blood volumes and renal function were similar to those found in the other group of patients when in the euthyroid state. We conclude that in primary hypothyroidism, ERPF and GFR are low, but that these values improve with substitutive therapy. CPV is a better index of the current plasma volume than APV. The difference between these two parameters suggests that the escape of albumin into the extravascular space in primary hypothyroidism is terminated by treatment. There are no clear abnormalities either in blood volumes or in renal function in subclinical hypothyroidism.
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              Impaired water excretion in myxedema.


                Author and article information

                Am J Nephrol
                American Journal of Nephrology
                S. Karger AG
                February 2004
                16 February 2004
                : 24
                : 1
                : 41-45
                Department of Nuclear Medicine, University of Vienna, Vienna, Austria
                75628 Am J Nephrol 2004;24:41–45
                © 2004 S. Karger AG, Basel

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                Tables: 2, References: 27, Pages: 5
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