Assesment of attainment of recommended TSH levels and levothyroxine compliance in differentiated thyroid cancer patients

Abstract

Objective: Thyroid-stimulating hormone (TSH) suppression treatment can induce signs and symptoms of hyperthyroidism and hypothyroidism due to inappropriate treatment or poor compliance to the treatment. The current study aimed to investigate TSH levels, frequency of being on target TSH, adherence to levothyroxine (LT4) suppression treatment in differentiated thyroid cancer (DTC) patients after surgery in a multicentric setting.

Design and patients: This multicentric cross-sectional study was conducted at 21 medical centres from 12 cities in Turkey. DTC patients followed at least one year in the same center included in the study. Clinical data, serum TSH, free thyroxine (FT4), thyroglobulin (Tg) and anti-Tg levels were recorded during the most recent visit. Body mass index, systolic and diastolic blood pressures, pulse rate were measured. LT4 doses were recorded and doses per kilogram of bodyweight were calculated. Pill ingestion habits recorded and adherence to the therapy were evaluated using the Morisky Medication Adherence Scale and categorized as good, moderate or poor compliant based on their scores. Risk stratification forpredicting the disease persistance and/or reccurence was assessed using the American Joint Committee on Cancer-7th edition thyroid cancer staging calculator. TSH serum concentrations were classified as severe suppression (TSH < 0.01 mU/L), moderate suppression (TSH: 0.01-0.1 mU/L), mild suppression (TSHL 0.1-0.5 mU/L), euthyroid (TSH: 0.5-4 mU/L) and hypothyroid (TSH > 4 mU/L). TSH levels can also be classified as on being on target, under the target, or beyond over the target, according to the American Thyroid Association recommendations.

Results: A group of 1125 patients (F/M: 941/184, 50.7 ± 11.7 years) were included in the study. The mean LT4 daily dosage was 132.4 ± 39.6 mcg/day. TSH levels showed severe suppression in 99 (%8.8) patients, moderate suppression in 277 (%24.6) patients and mild suppression in 315 (%28) patients and euthyroid range in 332 (%29.5) patients and hypothyroid range in 97 (8.6%). TSH levels were in target in 29.2% of the patients 20.4% of the patients were undertreated, 50.4% overtreated. The daily LT4 dose and LT4 dose/kg were significantly higher in the severe suppression group (p < .001, p < .001). According to the Morisky scale, 564 patients (50.1%) were good compliant, 368 patients (32.7%) were moderate compliant, and 193 patients (17.1%) were noncompliant. Patients with poor compliance need a higher dose of LT4 compared to the good compliance group (p < .001). TSH levels of patients with good compliance were 0.67 ± 1.96 mU/L and TSH with poor compliance was 2.74 ± 7.47 mU/L (p < .001). TSH levels were similar in patients on fixed and alternating dosages.

Conclusion: In 29.2% of the DTC patients, serum TSH levels were at target levels. Remaining of the study group have TSH levels under or over treatment range, exposing the patient to medication side effects. Majorty of the study group 82.8% have good or moderate adherence to LT4 therapy. Reaching TSH targets requires simplified and applicable guidelines and following the guideline recommendations.

Keywords: hormones/related; levothyroxine; thyroid; thyroid cancer; thyroid function tests; thyrotropin.