Effects of calorie intake and sampling time on thyroid stimulating hormone concentration

BackgroundThis study aimed to investigate the effects of blood collected after calorie intake on the level of thyroid stimulating hormone (TSH), comparing with the blood collected in fasting state.MethodsThis study was a prospective, randomized, controlled study. Subjects from the outpatients in the department of endocrinology without evident of thyroid diseases were included and then randomized into the fasting group, diet intake group, and glucose intake group, respectively. Fasting blood was collected from all the subjects at 7:00 am for the measurement of TSH and free thyroxine (FT4). Afterward, the subjects were maintained at fasting state (fasting group), had an intake of the mixed diet with the calories of 400 Kcal (diet intake group), and had an intake of 75 g glucose (glucose intake group), respectively, and blood was acquired again 2 h later (9:00 am on the same day) for TSH and FT4 measurement. The levels between 7:00 am and 9:00 am were compared.ResultsOf the 150 subjects, 146 met the inclusion criteria, of which 48, 48, and 50 were in the diet intake group, glucose intake group, and fasting group, respectively. The TSH in the diet intake group was significantly lower at 9:00 am (TSH9am) than the level at 2h before (TSH7am) (P<0.001), of which the median variation was -0.71 mU/L, and the median variation rate was -32.4%. In the glucose intake group, the TSH9am was also significantly lower than TSH7am (P<0.001), of which the median variation was -0.73 mU/L, and median variation rate was -31.5%. While in the fasting group, the TSH9am decreased slightly but statistically significantly lower than TSH7am (P<0.001), of which the median variation was -0.1 mU/L, and the median variation rate was -5.2%. According to TSH7am, 9 subjects in total (3 subjects in each group) met the diagnostic criteria of subclinical hypothyroidism. However, according toTSH9am, only 2 patients in the fasting group still met the diagnostic criteria of subclinical hypothyroidism.ConclusionComparing with the fasting state, the TSH level at 2h after the calorie intake was decreased by about 30%, which could influence the diagnosis of subclinical hypothyroidism.Trial registrationChiCTR2100047454.