The impact of time of sample collection on the measurement of thyroid stimulating hormone values in the serum

The aim of our research is to determine whether the time of blood sampling and fasting of patients have an impact on TSH values. A total of 198 participants were enrolled in this study and classified into five groups: A — the first sample collection for TSH measurement was taken between 7:00 and 8:00a.m. at fasting and the second after 140min without food intake; B — between 7:00 and 8:00a.m. at fasting and the second after 140min with food intake; C — between 7:00 and 8:00a.m. at fasting the previous day and the second one between 7:00 and 8:00a.m. at fasting the following day; D — between 9:00 and 10:00a.m. at fasting the previous day and the second one between 9:00 and 10:00a.m. at fasting the following day, and E — between 9:00 and 10:00a.m. at fasting the previous day and the second one between 7:00 and 8:00a.m. on the following day. Serum TSH concentration was measured by electrochemiluminescence immunoassay (ECLIA, Roche Diagnostics, Mannheim, Germany). TSH values (mIU/L) were in group A: 2.50 (2.20–2.81) first samples, 1.74 (1.52–1.96) second samples, p