Circadian and individual variability of TSH level in patients received replacement therapy for primary hypothyroidism

Abstract

Objective: to investigate circadian and individual variability of TSH level in patients taking LT4-replacement therapy for primary hypothyroidism. Methods. 22 patients taking LT4-replacement therapy, at the age of 18–60 years have been included. Measurements of serum TSH were performed at 8.00–9.00 h and 14.00–16.00 during the day and at 8.00–9.00 h in 4–6 weeks. Results. The median of TSH concentrations in the morning was 3.3 mU/l, at the day-time – 2.2 mU/l (р <0.05). The amplitude of TSH circadian variability reached 65% (Me-31.2%). According to the current TSH target ranges (0.4–4.0 mU/l) replacement therapy of 45.5% participants in the morning and 9% participants at the daytime has appeared inadequate. According to the proposed TSH target ranges (0.4–2.5 mU/l) 54.5% participants in the morning and 40% participants at the daytime had no hypothyroidism compensation. TSH levels in 4–6 weeks differed from initial on (+95)–95%. In 4–6 weeks replacement therapy has appeared inadequate in 21.4% participants according to the current TSH target ranges and in 35.7% participants according to the proposed TSH target ranges. Conclusion. The leading role in an estimation of adequacy of LT4 replacement therapy is played by morning TSH level. Difficulties of maintenance of TSH concentration exist both within current and proposed target range.