scholarly journals SAT-443 Impact of Fasting on Plasma Thyrotropin in Hypothyroid Patients Taking Levothyroxine During Ramadan (IFT-R Study)

2020 ◽  
Vol 4 (Supplement_1) ◽  
Author(s):  
Samer El-Kaissi ◽  
Laila AbdelWareth ◽  
Ruba Dajani ◽  
Terrence Lee St John ◽  
Sherry Ann Santarina ◽  
...  
Keyword(s):  
Thyroid Function ◽  
P Value ◽  
Thyroid Function Tests ◽  
Free T4 ◽  
Fasting Period ◽  
Function Tests ◽  
Number Of Patients ◽  
The Mean ◽  
Group 2 ◽  
Hypothyroid Patients

Abstract Background and Aim: We previously showed in a retrospective analysis that the plasma TSH rises significantly post-Ramadan in levothyroxine-treated hypothyroid patients, possibly as a result of changes in the eating habit during the non-fasting period from dusk until dawn. The aim of this study is to determine the best time for taking levothyroxine during Ramadan in order to minimize changes in thyroid function tests. Methods: in a randomized prospective design, hypothyroid patients taking levothyroxine for greater than 6-months were randomized to take levothyroxine at one of the following 3 times during Ramadan: (group 1) at dusk after a prolonged fast and 30-minutes before the Iftar meal, (group 2) ≥ 3-hours after the Iftar meal, or (group 3) at dawn 30-minutes before Suhur meal. Patients were instructed to allow a minimum of 3-hours between the last meal and levothyroxine and to refrain from eating and drinking for at least 30-minutes after taking levothyroxine. Thyroid function tests were performed within 3-months before Ramadan and within 6-weeks post Ramadan. To estimate intent-to-treat effects, we examined pre- and post-Ramadan thyroid function tests in relation to the assigned levothyroxine administration times. Results: 147 patients were randomized into the study and the respective number of patients in groups 1, 2 and 3 were 50, 46 and 51. The mean age of participants was 43.5±12.4 years [range 21.0-86.0] and 78% were females with no statistical differences in the mean age or gender distribution between the 3 groups. The respective pre-Ramadan mean TSH values for the 3 groups were 2.49 mIU/L, 2.16 mIU/L and 3.37 mIU/L with no significant differences at baseline. Post-Ramadan mean TSH values were 2.47 mIU/L, 4.26 mIU/L and 3.85 mIU/L for groups 1, 2 and 3 respectively. The pre- and post-Ramadan mean TSH differences were significant only for group 2, who took levothyroxine 3-hours post-Iftar (P-value 0.041). There were no significant differences in the free-T4 levels across the 3-groups before and after Ramadan. In a subset of 85 patients, the preferred times for levothyroxine administration during Ramadan were 44.7% before Iftar, 50.6% post-Iftar and only 4.7% were in favor of taking the medication before Suhur meal. Conclusions: Levothyroxine-treated hypothyroid patients who took levothyroxine 3-hours after the main Iftar meal showed a significant increase in plasma TSH post-Ramadan, possibly reflecting a reduced time period between levothyroxine administration and the previous meal. There was no significant change in the mean plasma TSH for patients taking levothyroxine at dusk before Iftar or at dawn before Suhur. The least patient-preferred time for taking levothyroxine was at dawn before Suhur possibly due to time constraints before the start of fasting.

scholarly journals Levothyroxine Administration during Ramadan: A Prospective Randomized Controlled Trial

2021 ◽  
pp. 1-6
Author(s):  
Samer El-Kaissi ◽  
Laila AbdelWareth ◽  
Ruba Dajani ◽  
Terrence J. Lee-St. John ◽  
Sherry Ann Santarina ◽  
...  
Keyword(s):  
Thyroid Function ◽  
Controlled Trial ◽  
Thyroid Stimulating Hormone ◽  
Thyroid Function Tests ◽  
Time Restrictions ◽  
Function Tests ◽  
Group 3 ◽  
Group 2 ◽  
Hypothyroid Patients ◽  
Group 1

<b><i>Background and Aim:</i></b> We have previously shown in a retrospective analysis that the plasma thyroid-stimulating hormone (TSH) rises significantly post-Ramadan in levothyroxine-treated hypothyroid patients, possibly as a result of lifestyle alterations and time restrictions during the nonfasting period from dusk until dawn. The aim of this study is to determine the best time to instruct patients to take levothyroxine during Ramadan so as to minimize changes in thyroid function tests during this period. <b><i>Methods:</i></b> In a randomized prospective design, hypothyroid patients taking levothyroxine were randomized to receive instructions to take levothyroxine at one of the following 3 times during Ramadan: (group 1) at dusk 30-min before Iftar meal, (group 2) 3 or more hours after Iftar meal, or (group 3) at dawn 30-min before Suhur meal. Thyroid function tests were performed within 3 months before Ramadan and within 6 weeks post-Ramadan. Data from patients with at least 1 blood test before or after Ramadan were analyzed using mixed-effects regression models. <b><i>Results:</i></b> Plasma TSH levels were available at one or more time points for 148 patients, group 1 (<i>n</i> = 50), group 2 (<i>n</i> = 46), and group 3 (<i>n</i> = 52). A statistically significant within-patient increase in plasma TSH was seen in patients at the 25th percentile pre-Ramadan in groups 2 and 3 (<i>p</i> values &#x3c;0.001), but not in group 1. A statistically significant within-patient decrease in plasma TSH was found in patients at the 75th percentile in group 1 only. For patients at the 50th percentile pre-Ramadan, no statically significant within-patient changes were found, though descriptively, increases in plasma TSH were observed for groups 2 and 3, while a decrease was observed in group 1. <b><i>Conclusions:</i></b> Our data suggest that instructing patients to take levothyroxine at the time of breaking the fast 30 min before the Iftar meal minimizes unfavorable changes in plasma TSH post-Ramadan. In contrast, instructing patients to take levothyroxine 3 h post-Iftar or 30 min before Suhur led to a greater rise in post-Ramadan TSH.

IMPACT OF LIFESTYLE CHANGES DURING RAMADAN ON THYROID FUNCTION TESTS IN HYPOTHYROID PATIENTS TAKING LEVOTHYROXINE

2020 ◽  
Vol 26 (7) ◽  
pp. 748-753
Author(s):  
Samer El-Kaissi ◽  
Ruba Dajani ◽  
Terrence J. Lee-St. John ◽  
Sherry Ann Santarina ◽  
Fiona Makia ◽  
...  
Keyword(s):  
Thyroid Function ◽  
Older Patients ◽  
Thyroid Stimulating Hormone ◽  
Lifestyle Changes ◽  
Interquartile Range ◽  
Thyroid Function Tests ◽  
Function Tests ◽  
The Mean ◽  
Hypothyroid Patients ◽  
Stimulating Hormone

Objective: The holy month of Ramadan poses a challenge for levothyroxine-treated patients due to altered eating habits and time restrictions. The aim of this study was to examine the impact of lifestyle changes during Ramadan on thyroid function tests in hypothyroid patients taking levothyroxine in the United Arab Emirates. Methods: Retrospective design whereby levothyroxine-treated hypothyroid patients who had thyroid function tests within 3 months pre-Ramadan and within 2 months post-Ramadan were included. We looked at adherence to levothyroxine, eating pattern, and levothyroxine administration in relation to meal times during Ramadan. Pre- and post-Ramadan thyroid function tests and the potential impact of independent variables using a random-intercept mixed effects linear model were examined. Results: A total of 112 patients (89 females) were recruited in the study, with a mean age ± standard error (SE) of 44.70 ± 1.36 years (range, 19.0 to 79.0 years). The mean thyroid-stimulating hormone (TSH) within 3 months before Ramadan was 1.809 ± 0.094 mIU/L (median, 41.5 days; interquartile range [IQR], 25.0 to 73.0 days), while the mean TSH within 2 months post-Ramadan was higher at 3.072 ± 0.312 mIU/L (median, 27.5 days; IQR, 14.0 to 42.0 days). Post-Ramadan, 36 out of 112 patients had a plasma TSH outside of the normal reference range. The independent variable outcomes model showed that older patients and males were more likely to have an increased plasma TSH post-Ramadan. There was no relationship between the time of levothyroxine administration and change in TSH level. Conclusion: Levothyroxine-treated hypothyroid patients showed a significant increase in plasma TSH post-Ramadan, amounting to 2.525 standard deviations, with older patients and males more likely to be affected. Abbreviations: IQR = interquartile range; T4 = thyroxine; TSH = thyroid-stimulating hormone

scholarly journals A comparative study on outcomes of preprandial versus postprandial thyroid function test

2019 ◽  
Vol 5 (6) ◽  
pp. 1662
Author(s):  
Vasim Ismail Patel ◽  
Akshay B. K.
Keyword(s):  
Thyroid Function ◽  
Subclinical Hypothyroidism ◽  
Clinical Symptoms ◽  
Thyroid Function Test ◽  
Thyroid Stimulating Hormone ◽  
Endocrine Gland ◽  
Thyroid Function Tests ◽  
Sample Collection ◽  
Free T4 ◽  
Group 2

<p class="abstract"><strong>Background:</strong> The thyroid is an<strong> </strong>endocrine gland. It secretes two hormones thyroxine (T<sub>4</sub>), triiodothyronine (T<sub>3</sub>). Hypothyroidism is a common condition encountered by a clinician. Subclinical hypothyroidism (SCH) defined as normal free thyroxine (T4) and elevated thyroid stimulating hormone (TSH), is primarily a biochemical diagnosis with or without clinical symptoms. Studies have observed that TSH levels vary at different times in a day. In practice not much importance is given to the timing of the sample collection (pre-prandial or post-prandial sate). SCH is diagnosed depending on TSH value. So the condition may be under or over diagnosed based on a single value. So we conducted this study to determine whether timing of sample collection had any significant relationship in the determination of levels of thyroid hormones.</p><p class="abstract"><strong>Methods:</strong> The study was carried on 114 patients who visited ENT department, NMCH between July 2018 and June 2019. Group-1 consisted of 38 normal patients. Group-2 consisted of 36 hypothyroidism patients GROUP-3 consisted of 40 subclinical hypothyroidism patients. Thyroid function tests (TSH and free T4) were done in fasting state and 2 hours postprandially.  </p><p class="abstract"><strong>Results:</strong> TSH values were found to be significantly lowered after food in all the three groups. Free T4 values did not show any statistically significant alteration after food.</p><p class="abstract"><strong>Conclusions:</strong> There was a significant decline in TSH values postprandially. This might lead to inappropriate diagnosis and management of patients as cases of hypothyroidism, especially in cases of sub clinical hypothyroidism.</p>

scholarly journals THERAPY OF ENDOCRINE DISEASE: T4 + T3 combination therapy: is there a true effect?

2017 ◽  
Vol 177 (6) ◽  
pp. R287-R296 ◽  
Author(s):  
Wilmar M Wiersinga
Keyword(s):  
Combination Therapy ◽  
Thyroid Function ◽  
Healthy Subjects ◽  
Randomized Clinical Trials ◽  
Peripheral Tissue ◽  
Thyroid Function Tests ◽  
Peripheral Tissues ◽  
Persistent Symptoms ◽  
Function Tests ◽  
Number Of Patients

About 5%–10% of hypothyroid patients on T4 replacement therapy have persistent symptoms, despite normal TSH levels. It was hoped that T4 + T3 combination therapy might provide better outcomes, but that was not observed according to a meta-analysis of 11 randomized clinical trials comparing T4 monotherapy with T4 + T3 combination therapy. However, the issue is still subject of much research because normal thyroid function tests in serum may not necessarily indicate an euthyroid state in all peripheral tissues. This review evaluates recent developments in the field of T4 + T3 combination therapy. T4 monotherapy is associated with higher serum FT4 levels than in healthy subjects, and subnormal serum FT3 and FT3/FT4 ratios are observed in about 15% and 30% respectively. T4 + T3 combination therapy may mimic more closely thyroid function tests of healthy subjects, but it has not been demonstrated that relatively low serum FT3 or FT3/FT4 ratios are linked to persistent symptoms. One study reports polymorphism Thr92Ala in DIO2 is related to lower serum FT3 levels after thyroidectomy, and that the D2-Ala mutant reduces T4 to T3 conversion in cell cultures. Peripheral tissue function tests such as serum cholesterol reflect thyroid hormone action in target tissues. Using such biochemical markers, patients who had a normal serum TSH during postoperative T4 monotherapy, were mildly hypothyroid, whereas those with a TSH 0.03–≤0.3 mU/L were closest to euthyroidism. Peripheral tissue function tests suggest euthyroidism more often in patients randomized to T4 + T3 rather than that to T4. Preference for T4 + T3 combination over T4 monotherapy was dose-dependently related to the presence of two polymorphisms in MCT10 and DIO2 in one small study. It is not known if persistent symptoms during T4 monotherapy disappear by switching to T4 + T3 combination therapy. The number of patients on T4 + T3 therapy has multiplied in the last decade, likely induced by indiscriminate statements on the internet. Patients are sometimes not just asking but rather demanding this treatment modality. It creates tensions between patients and physicians. Only continued research will answer the question whether or not T4 + T3 combination therapy has true benefits in some patients.

scholarly journals SUN-425 Indiscriminate Thyroid Function Testing on Acute Hospital Admissions Reveals a High Abnormality Rate Requiring Follow Up

2020 ◽  
Vol 4 (Supplement_1) ◽  
Author(s):  
Robert P McEvoy ◽  
Anthony O’Riordan ◽  
Mark J Hannon
Keyword(s):  
Thyroid Function ◽  
American Thyroid Association ◽  
Thyroid Function Tests ◽  
Free T4 ◽  
Patient Age ◽  
Function Tests ◽  
Patient Âgé ◽  
Thyroid Function Testing ◽  
Function Testing

Abstract The population attending the Medical Assessment Unit at our hospital comprises patients attending electively for investigation and acutely unwell patients presenting for unscheduled care. The standard panel of blood tests taken on arrival includes thyroid function tests (TFTs, i.e. TSH and free-T4), despite a recent review questioning the clinical utility of this practice [1]. We performed a retrospective audit to determine what proportion of our patients had abnormal thyroid function on presentation, and whether these abnormal test results were being followed up. Using the iSoft Clinical Manager software, a list was generated of all patients who attended the hospital between January 2018 and June 2018 inclusive. For each attendance, we recorded the date, medical record number, patient age, gender, and TFT result. Abnormal TFT results were classified as overt or subclinical hyper- or hypothyroid, or non-thyroid illness syndrome (NTIS), based on their admission TSH and free-T4. We then examined the hospital and primary care records of patients with abnormal TFTs to determine if they had ongoing thyroid follow up post discharge. In total, 2,298 patients attended over the 6-month study period. The mean patient age was 67.2 years, and 49% were female. Thyroid function tests were ordered on the day of attendance for 1,688 patients (73%). Of these, 181 results (11%) were abnormal: 20 overt hyperthyroid (11%), 72 subclinical hyperthyroid (40%), 12 overt hypothyroid (7%), 35 subclinical hypothyroid (19%), and 42 NTIS (23%). Twenty of these patients died within 3 months of the abnormal TFT result (4 overt hyperthyroid, 3 subclinical hyperthyroid, 3 overt hypothyroid, 6 subclinical hypothyroid, and 4 NTIS). Of the remaining 161 patients, 74 (46%) had not been followed up within 3 months (4 overt hyperthyroid, 34 subclinical hyperthyroid, 3 overt hypothyroid, 15 subclinical hypothyroid, and 18 NTIS). The low percentage of abnormal TFTs (11%) in this audit is in keeping with similar studies where thyroid function testing was performed on unselected hospital populations [1]. Subclinical hyperthyroidism was by far the most common abnormality found. A high percentage of abnormal tests (46%) were not followed up, with poor compliance with thyroid management guidelines [2]. Future work will investigate adoption of an ‘opt-in’ order system [3] and electronic alerts to flag abnormal results for follow-up. [1] Premawardhana LD. Thyroid testing in acutely ill patients may be an expensive distraction. Biochemia medica. 2017; 27(2): 300-307. [2] Ross DS et al. 2016 American Thyroid Association Guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosis. Thyroid. 2016 Oct; 26(10):1343-1421. [3] Leis B et al. Altering standard admission order sets to promote clinical laboratory stewardship: a cohort quality improvement study. BMJ Qual Saf. 2019; 28(10): 846-52.

scholarly journals Lyme Disease: An Autoimmunity-Based “Destructive Thyroiditis” or Just Another “Non-Thyroidal Illness”?

2021 ◽  
Vol 5 (Supplement_1) ◽  
pp. A940-A941
Author(s):  
Nyembezi Dhliwayo ◽  
Rana Wajahat ◽  
Andriy Havrylyan ◽  
Alvia Moid ◽  
Walid Khayr ◽  
...  
Keyword(s):  
Lyme Disease ◽  
Thyroid Function ◽  
Paranoid Schizophrenia ◽  
Thyroid Autoimmunity ◽  
Thyroid Peroxidase ◽  
Thyroid Function Tests ◽  
Free T4 ◽  
Radioiodine Uptake ◽  
Function Tests ◽  
Antigenic Properties

Abstract There is considerable evidence that some Borrelial (Lyme spirochetal) proteins share significant antigenic properties with several thyroid-related proteins (e.g. TSH receptor, thyroglobulin, thyroid peroxidase) and can induce thyroid autoimmunity, sometimes associated with Hashimoto’s thyroiditis and perhaps also a “destructive thyroiditis” such as “silent” thyroiditis or “Hashitoxicosis.” As an acute illness, Lyme disease may also constitute a “non-thyroidal illness” capable of perturbing thyroid function tests without causing thyroid dysfunction. We report a 22-year old woman admitted with an acute paranoid schizophrenia, thyroid function tests consistent with autoimmunity, transient thyrotoxicosis (tachycardia, lid-lag, brisk DTR’s) and a greatly reduced radioiodine uptake. The thyroid was not palpably enlarged, nodular or tender. On screening assay, reactivity was demonstrated to 4 of 13 Borrelial proteins. Anti-Lyme IgM but not IgG, antibodies, were positive. This was consistent with recent Lyme disease infection. Serum TSH (NL: 0.358-3.74 mcU/ml), Free T4 (NL: 0.76-1.46 ng/dl), and Free T3 (NL: 2.18-3.98 pg/ml) were, respectively: Day1: 0.087 mcU/ml (suppressed), 1.52 ng/dl (slightly elevated), 2.07 pg/ml (slightly reduced); Day2: 0.148 (suppressed), 1.18 (normal), no FT3; Day4: 0.827 (normal), no FT4 or FT3; Day5: 1.66 (normal), 0.89 (normal), 1.77 (low). Anti-Tg and Anti-Peroxidase antibodies were both moderately elevated. Thyroid Stimulating Immunoglobulins were not elevated. The radioactive iodine uptake on Day4 was 2.8% (NL: 15-30% at 24 hr). Thyroid ultrasonogram was normal. An attractive explanation is that Lyme disease triggered a “destructive thyroiditis,” perhaps but not necessarily mediated by thyroid autoimmunity. This would account for the brief interval of thyrotoxicosis accompanied by a very low radioiodine uptake. Alternatively, Lyme disease, as an acute process, would expectedly be capable of eliciting the thyroid function abnormalities of “non-thyroidal illnesses” in general, as would acute psychosis, well-known to often resemble Graves’ disease at admission.

scholarly journals The method comparison and the verification of precision of Mindray CL-6000i thyroid function tests (TFTs)

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Giray Bozkaya ◽  
Ali Rıza Şişman
Keyword(s):  
Thyroid Function ◽  
Method Comparison ◽  
Endocrine Disorders ◽  
Thyroid Function Tests ◽  
Good Precision ◽  
Serum Samples ◽  
Function Tests ◽  
The Mean ◽  
The Difference ◽  
Mean Differences

AbstractObjectivesThyroid diseases are the most frequent endocrine disorders and thyroid function tests (TFTs) are the most commonly requested endocrine tests. The reliable measurements of these tests are quite important. The aim of our study was to determine the bias and to verify the precision of the newly introduced Mindray CL-6000i immunoassay system in the guidance of CLSI guidelines.MethodsA precision and bias study was performed in Mindray CL-6000i analyzer for FT3, FT4, TSH, Anti-TG, and Anti-TPO tests by using BioRad quality control (QC) materials and serum samples, respectively. Bland–Altman difference plot and Passing-Bablok regression analysis was made for method comparison with Beckman Coulter DXI 800 analyzer.ResultsThe repeatability coefficient of variations (CVs) of FT3, FT4, TSH, Anti-TG, and Anti-TPO tests were ≤2.36, ≤1.66, ≤2.38, ≤3.48, and ≤3.31% while within laboratory CVs were ≤2.85, ≤4.61, ≤2.59, ≤3.78, and ≤3.60%, respectively. The mean differences between the two methods obtained from Bland–Altman analysis for FT3, FT4, TSH, Anti-TG, and Anti-TPO were defined to be −19%, 1.95%, −5.9%, −3.5%, and 7.3%, respectively.ConclusionsMindray CL-6000i had good precision in all tests, but the difference between the two methods in some tests shows that the harmonization and standardization of TFTs initiated globally is required.

scholarly journals The Relationship Between Thyroid Function and Body Composition, Leptin, Adiponectin, and Insulin Sensitivity in Morbidly Obese Euthyroid Subjects Compared to Non-obese Subjects

2021 ◽  
Vol 14 ◽  
pp. 117955142098852
Author(s):  
Ohoud Al Mohareb ◽  
Moath Al Saqaaby ◽  
Aishah Ekhzaimy ◽  
Muaawia Hamza ◽  
Mussa H. AlMalki ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Body Composition ◽  
Thyroid Function ◽  
P Value ◽  
Morbidly Obese ◽  
Thyroid Function Tests ◽  
Free T4 ◽  
Obese People ◽  
Unit Increase ◽  
Obese Subjects

Background/Objectives: Thyroid function tests (TFTs) changes in obese people have been studied with increasing interest, however, studies have been inconsistent hence it remains poorly understood. We compared the TFTs of morbidly obese euthyroid Saudi subjects with non-obese controls and then we examined the influence of leptin, adiponectin, and insulin resistance on TFTs. Subjects/Methods: Fifty-five euthyroid obese subjects attending bariatric surgery clinic and 52 non-obese age-and gender-matched controls were recruited. We measured body weight, BMI, body composition, thyroid-stimulating hormone (TSH), Free T4 (FT4), Free T3(FT3), thyroid antibodies, fasting leptin, adiponectin, and lipid profile. Insulin resistance was quantified by HOMA-IR. Data are presented as mean ± SEM. Results: Mean BMI was 45.6 ± 1.5 and 23.2 ± 0.5 kg/m2, for the obese and non-obese controls, respectively, P value < 0.001. Mean TSH was 2.7 ± 0.18 mIU/L in obese subjects and 1.7 ± 0.13 mIU/L (0.27-4.2) in the non-obese controls, respectively, P value .014. Mean FT3 was 3.9 ± 0.1 pmol/L (3.1-6.8) in obese subjects compared to 5.0 ± 0.1 pmol/L in non-obese controls, respectively, P value 0.001, however, FT4 was similar in the 2 groups. In the whole group ( N = 107), BMI correlated positively with TSH and negatively with FT3. Leptin correlated negatively with both FT4 and FT3 in the non-obese group only while none of the TFTs correlated with HOMA-IR or adiponectin in either group. Binary logistic regression showed that each 1 unit increase in TSH increased the odds of becoming obese by 12.7, P value 0.009, 95 C.I. (1.9-85.0). Conversely, each - unit increase in FT3 decreased the odds of becoming obese by 0.2, P value 0.023, 95% C.I. (0.05-0.80). Conclusions: We report a small increase in TSH and a small decrease in FT3 within the normal range in obese subjects compared to non-obese controls. We also report a positive correlation between TSH and BMI with increased odds ratio of becoming obese with the increase in TSH and decrease in FT3. These changes may be either causally related or adaptive to the obesity state. FT4 and FT3 seem to correlate with leptin (but not with adiponectin or HOMA-IR) in the non-obese controls only. Larger mechanistic studies are needed to further elucidate the interesting association between obesity and TFTs.

Diurnal variation in TSH and free thyroid hormones in patients on thyroxine replacement

1989 ◽  
Vol 121 (5) ◽  
pp. 674-676 ◽  
Author(s):  
Ian Sturgess ◽  
Simon H. Thomas ◽  
Dudley J. Pennell ◽  
Derek Mitchell ◽  
Desmond N. Croft
Keyword(s):  
Thyroid Function ◽  
Peak Level ◽  
Thyroid Function Tests ◽  
Once Daily ◽  
Free Thyroid Hormones ◽  
Function Tests ◽  
Thyroxine Replacement ◽  
Thyroxine Replacement Therapy ◽  
Hypothyroid Patients ◽  
Trough Levels

Abstract. Eleven patients with treated hypothyroidism were investigated to examine the effects of time on their thyroid function tests. Each patient was clinically and biochemically euthyroid on once daily thyroxine replacement therapy, taken in the morning. TSH followed a diurnal rhythm with a peak level at 23.30 h and a trough level at 14.30 h. Four subjects had TSH trough levels within the normal range, but with peak levels outside this range. FT4 and FT3 levels fell from their highest levels some three hours after ingestion to the lowest levels just prior to the next dose. This study shows that there are significant time-related variabilities in TSH and thyroid hormone levels in treated hypothyroid patients. This should be taken into account when interpreting results of their thyroid function tests.

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