Background: TSH suppression below the reference range is not currently recommended for postoperative patients with differentiated thyroid cancer (DTC) at very low risk for recurrence. However, higher TSH levels may be associated with insufficient levothyroxine replacement and subsequent metabolic derangements such as dyslipidemia.
Methods: We reviewed 1092 women with DTC, who underwent total thyroidectomy at ages 19-79 years and were followed up with lipoprotein profiles at 1-4 years after the surgery. Postoperative changes in cholesterol levels were investigated according to the postoperative TSH levels. Multinomial multivariable logistic regression analyses were performed to assess the risks for dyslipidemia according to the TSH levels with adjustment for potential confounders including age, follow-up period, preoperative total cholesterol (TC), and body mass index.
Results: Preoperative to follow-up changes of TC were −3.69 mg/dL (P=0.006), +0.13 mg/dL (P=0.926), +12.46 mg/dL (P <0.001), and +16.46 mg/dL (P <0.001) in TSH <0.03, 0.03-0.3, 0.3-2.0, and 2.0-5.0 mIU/L groups. Compared with TSH 0.03-0.3 mIU/L, TSH 0.3-2.0 mIU/L was associated with hypercholesterolemia (Adjusted odds ratios [AOR] = 1.86 and 5.08 for TC 200-240 and ≥240 vs. <200 mg/dL, both P <0.01) and hyper-LDL-cholesterolemia (AOR = 2.76 for LDL cholesterol ≥160 vs. <130 mg/dL, P = 0.012). Moreover, TSH 2.0-5.0 mIU/dL was associated with higher risks for hypercholesterolemia (AOR = 2.85 and 6.95 for TC 200-240 and ≥240 mg/dL vs. <200 mg/dL, both P <0.01) and hyper-LDL-cholesterolemia (AOR = 2.08 and 4.17 for LDL cholesterol 130-159 and ≥160 mg/dL vs. <130 mg/dL, both P <0.05).
Conclusions: TC increased when thyroidectomized female DTC patients kept TSH levels within normal range. Thus, these patients had higher risks for hypercholerolemia and hyper-LDL-cholesterolemia. Risks for metabolic derangements by insufficient levothyroxine replacement should be considered when the less-intense TSH suppression is adopted in postoperative DTC patients.