Endocrine Abstracts

Introduction: Significant hyponatremia may evolve in hypothyroidism, when however, elevated ADH levels have not been consistently demonstrated. On the other hand, it was shown that thyroid hormone substitution suppresses ADH, and its surrogate marker copeptin secretion. The aim of our present study was to investigate the possible humoral changes in a special model of resolution of short term severe hypothyroidism in differentiated thyroid cancer (DTC) patients.

Patients: In 39 DTC patients (11 men, 28 women, mean age 50.28 ± 14.90 ys) in whom DTC was not advanced (ECOG: 0) blood samples were obtained on the day of radioiodine therapy and 10–12 weeks after thyroxine supplementation.

Results: Serum sodium (140.8 ± 2.6 vs 142.3 ± 1.8; P = 0.002), chloride (100.8 ± 3.4 vs 102.5 ± 2.6; P = 0.012), potassium (4.3 ± 0.4 vs 4.4 ± 0.3; P = 0.025), eGFR (77.0 [61.0–90.0] vs 90.0 [72.0–90.0]; P < 0.001), NT-proBNP (36.8 [20.6–73.7] vs 69.6 [37.4–194.9]; P < 0.001), ACTH (11.9 [10.0–16.0] vs 16.4 [12.2–22.5]; P = 0.001) and renin activity (0.7 [0.4–1.6] vs 1.6 [0.9–2.9]; P = 0.003) were lower during hypothyroidism, while cortisol, aldosterone and copeptin were similar. Of the investigated parameters copeptin showed positive association with sodium in univariate (r = 0.226; P = 0.046) and to TSH in multivariate correlations (R square = 0.123; P = 0.001). Serum sodium levels had a variance of 5.47 mmol/l and, beside copeptin, were associated to concentrations of TSH (r = −0.321; P = 0.004), ACTH (r = 0.349; P = 0.002) and cortisol (r = 0.225; P = 0.047). However, none of them were independent determinants of serum sodium levels in multiple regression analyses.

Conclusion: According to our investigations, TSH is an independent predictor of copeptin level. The serum sodium level is significantly lower in short term severe hypothyroidism, but this cannot be appropriately explained by the investigated humoral parameters.

Keywords: TSH, DTC, hypothyroidism, hyponatraemia, copeptin.