Predictors of Serum TSH in a Healthy Adult Sample of the Lebanese Population

Research Article

Annals Thyroid Res. 2022; 8(1): 373-378.

Predictors of Serum TSH in a Healthy Adult Sample of the Lebanese Population

Achkar AA1#, Mourad D2#, Naous E2, Sleilaty G3, Gannagé-Yared MH1,2*

¹Department of Laboratory Medicine and Endocrinology, Saint-Joseph University, Lebanon

²Department of Endocrinology, Saint-Joseph University, Lebanon

³Department of Biostatistics and Clinical Research Center, Saint-Joseph University, Lebanon

#These authors have contributed equally to this article

*Corresponding author: Marie-Hélène Gannagé-Yared, Division of Endocrinology, Hotel-Dieu de France Hospital, Beirut, Lebanon

Received: June 10, 2022; Accepted: July 11, 2022; Published: July 18, 2022


Purpose: Measuring thyroid-stimulating hormone (TSH) is essential for diagnosing and monitoring thyroid diseases. The aim of this study is to determine the factors predicting TSH variability.

Materials and Methods: Plasma TSH, free T3 (FT3), total T3 (TT3), free T4 (FT4), anti-peroxidase antibodies (TPOAb) and anti-thyroglobulin antibodies (TgAb) were measured in 301 healthy Lebanese adults (198 women and 103 men) aged 18 to 65 years. Measurements were performed on the Cobas Roche automate. Age, sex, Body Mass Index (BMI), arterial blood pressure and the presence of dyslipidemia were collected from the population.

Results: The mean age of the population was 38.98 ± 13.28 years and the mean BMI 25.36 ± kg/m². There was no correlation between TSH and FT4, while a positive correlation was found between TSH and TT3, FT3, TPOAb and TgAb (respectively p <0.001, p=0.002, p<0.0001and p< 0.0001). TSH was not associated with age or gender but was positively correlated with BMI (p=0.053) and systolic blood pressure (p=0.03).In a multiple linear regression analysis, the independent predictors of TSH were FT4, FT3 and TPOAb. In addition, FT4, TPOAb, and dyslipidemia were independently associated with the TSH 97.5th percentile.

Conclusion: Our study showed that the main predictors of TSH are FT4, FT3 and TPOAb. This finding supports the role of TSH in enhancing T3 production as well as the main role of TPOAb in predicting the rise in TSH.

Keywords: TSH; Predictors; Lebanese; Healthy; Adults


TSH (Thyroid stimulating hormone) is the most sensitive marker for assessing the thyroid status and is considered by the American Thyroid Association (ATA) as the most helpful test for screening thyroid dysfunction [1].

Serum TSH secretion is pulsatile [2] and exhibits a diurnal variation with a nocturnal peak leading to intraindividual TSH variations depending on the time of blood withdrawal during the day [3,4] Serum TSH is also affected by acute stress [5] and varies according to age [3,6,7], sex [3,7], BMI [8] and iodine status [9]. TSH increases with BMI [10,11], is higher in females [12] and elderly people [12]. Some studies have also reported an increased prevalence of hypertension [13] and dyslipidemia [14] with the increase in TSH levels. Finally, the presence of antithyroid antibodies, either thyroid peroxidase antibodies (TPOAb) [15,16] or thyroglobulin antibodies (TgAb) [16], is associated with higher TSH values, with a stronger relationship with the former [15].

No previous studies were conducted in the Middle East to establish factors that can influence the variability of TSH. The aim of this study was to identify predictive factors of TSH variation in a healthy adult sample of the Lebanese population.

Materials and Methods


This is a cross-sectional study conducted on a sample of Lebanese subjects aged between 18 and 65 years. Recruitment was done between November 2020 and January 2021 based on volunteering among healthy hospital employees and visitors. Were excluded from the study: subjects with a personal history of thyroid disease or clinical goiter, or with any recent acute stress (hospitalization or acute infection within the last month) or chronic diseases (such as hepatic or renal disease), as well as subjects on medication that can affect thyroid tests (such as levothyroxine, oral contraceptives, estrogen replacement therapy, glucocorticoids or biotin) or pregnancy.

On the day of sampling, height in meter (m) and weight in kilogram (kg) of all participants were measured. Height was measured without shoes using a wall mounted tape. Weight was measured without shoes and with light clothes on using a calibrated scale (Soehnle Professionals).

Body mass index (BMI) was calculated as weight (in kilograms) divided by the squared value of height (in meters) and expressed in kg/m². BMI was divided into 3 subclasses: underweight for a BMI<18 kg/m², normal weight for a BMI between 18 and 25 kg/m², overweight for a BMI between 25 and 30 kg/m², and obese for a BMI superior to 30 kg/m². Systolic and diastolic arterial pressures were taken in a sitting position after 5 minutes of rest.

All participants signed an informed written consent, and the study was approved by the Ethics Committee at Hôtel-Dieu de France university hospital, Beirut, Lebanon (CEHDF1524).

Biological Analysis

For all the subjects enrolled in the study, fasting blood samples were collected at the laboratory of the authors’ institution between 8 and 10 am, then were centrifuged on the day of collection, and the resulting serum frozen at -20°C for <2 months before biochemical measurements: TSH, free T4 (FT4), free T3 (FT3), and total T3 (TT3), Thyroid antibodies (TPOAb and TgAb). Measurements were performed on the fully automated Cobas Core electrochemiluminescence (ECL) technology immunoassay system (Roche Cobas e411). The respective reference ranges defined by the manufacturer for TSH, FT4, FT3, TT3, TPOAb, and TgAb are defined as 0.27- 4.2 μIU/mL, 12-22 pmol/L, 3.1 - 6.8 pmol/L, 1.3 - 3.1 nmol/L, < 34 IU/mLand < 115 IU/mL. For all the biological parameters the coefficient of variation is less than 8%.

Statistical Analysis

The distribution of the biological values (TSH, FT4, FT3, TPOAb and TgAb) was checked using Shapiro-Wilk (SW) tests and visual inspection of the quartile-quartile (Q-Q) graphics. Native variables with a skewed distribution were expressed as a median value with an interquartile interval (quartile 1 - quartile 3) and the 95% distribution interval (percentile 2.5 - percentile 97.5). Correlations between the quantitative variables were estimated by the Spearman correlation coefficient for variables departing from normality, and by the Pearson correlation coefficient otherwise, including log-transformed variables. 95% Confidence intervals (95% CI) for Spearman’s rho were derived by bootstrapping based on 10,000 samples. The Student test, the Mann-Whitney test, the Chi-square test were used as appropriate. TPOAb and TgAb antibodies’ levels, reported initially as <5 and <10 respectively, were considered to be equal to 5 and 9 respectively. In the multivariate analyses, a primary model of multiple linear regression was done to study the correlation between Ln (TSH) and the different independent variables. Model calibration used Cox-Snell R2, Cook distances and the studentized residuals. An additional quantile regression model was used to study the variations of percentile 2.5, percentile 50 (median) and percentile 97.5 with the independent factors. All statistical analyses were performed using IBM SPSS (IBM Corp; SPSS Statistics for Windows v26.1, Armonk, NY, USA).


Baseline Anthropometric and Socioeconomic Characteristics of the Sample

The sample consisted of 301 subjects, 103 men and 198 women (respectively 34.2% and 65.8%). Most of the participants were recruited from Beirut and Mount Lebanon areas (34.9% and 51.8% respectively). Demographic, anthropometric, and clinical characteristics of the sample, and according to sex are shown in (Table 1). The mean age was 39.0 ± 13.4 years, comparable in males and females (p=0.95). Men had a higher BMI (27.1 ± 4.7 vs 24.5 ± 4.6 Kg/m², p<0.001), had more frequently hypertension and dyslipidemia (p=0.07 and p=0.037 respectively). 29 subjects reported to have dyslipidemia of which 14 were treated by hypolipidemic agents and 26 reported to be hypertensive of which 21 treated by antihypertensive drugs.