Variability of thyroid-stimulating hormone indicators in clinical practice

Abstract

Determination of pituitary thyroid-stimulating hormone (TSH) is one of the most common tests in the world. The article examines the variability of the TSH level in the blood and its causes in the context of the reliability of the assessment of this indicator. The defi nition of the term of subclinical hypothyroidism, namely the level of TSH that should be the reason for prescribing thyroxine, is also discussed. Most authors today believe that, in general, when hypothyroidism is fi rst detected, the appointment of thyroxine is mostly required only when TSH >10 mU/L. The purpose of the study: to reveal the degree of discrepancies between two TSH measurements with an interval of no more than 7 days. The research materials were the results of repeated measurements of TSH (measured in mU/L) of patients for the period 2000-2023. A total of 316 such pairs of TSH measurements (with an interval of no more than a week) were found in the electronic register. Cases where the interval between measurements was 6, 5, 4, and 3 days were also analyzed. At the same time, there were 104 pairs of measurements with an interval of 3 days. Results and discussion. The majority of cases are within the TSH discrepancy of up to 10 mU/L, but a signifi cant number of diff erences between the two TSH measurements are greater than 10 mU/L, and may even reach more than 100 mU/L. It was established that there is no dependence on the time interval between two measurements, the age of the patient, as well as no correlation of the diff erence in TSH measurements with the year of measurement (2000-2023). We believe that discrepancies in TSH measurements within several days fi rst of all arise due to the presence of circadian rhythms, the pulsating nature of the secretion and the infl uence of external factors (diff erent time of sampling, availability of breakfast, etc.). Conclusions. The fi rst detected result of TSH outside the normal range should not be the basis for diagnosis of hypothyroidism and prescribing treatment, except for cases when it fully corresponds to clinical signs and urgent treatment is necessary to improve the patient's condition. If there is a discrepancy between the TSH result and the clinical picture, it is desirable to check the results in diff erent laboratories, determine free triiodothyronine and thyroxine. In any clinical cases, you should not try to maintain TSH within the narrow limits of few units, because the actual fl uctuations during measurement are greater, which makes such eff orts useless.