Thyroid Hormone Levels Affected by Time of Blood Sampling in Thyroxine-Treated Patients

Ain, Kenneth B.; Pucino, Frank; Shiver, Tiana; Banks, Steven M.

doi:10.1089/thy.1993.3.81

Cited by 47 publications

(19 citation statements)

References 17 publications

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“…Phlebotomy was performed between 8 and 10.30 AM with the patient in a fasting state. LT 4 administration was delayed until after phlebotomy for the postoperative profiles to obtain trough levels of thyroid hormones (37). Each thyroid profile consisted of a serum TSH, total T 4 , FT 4 , and total T 3 .…”

Section: Thyroid Profilesmentioning

confidence: 99%

Tandem Mass Spectrometry as a Novel Tool for Elucidating Pituitary–Thyroid Relationships

Jonklaas

Soldin

2008

Thyroid

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Background: Our objective was to determine the performance of liquid chromatography-tandem mass spectrometry (LC-MS=MS) in documenting both group and individual relationships between thyroid hormone and thyroid-stimulating hormone (TSH) concentrations. Methods: This was a prospective analysis of 50 euthyroid patients undergoing thyroidectomy. Thyroxine (T 4 ), triiodothyronine (T 3 ), free T 4 (FT 4 ), and TSH levels were documented on two occasions before thyroidectomy. After thyroidectomy, patients were treated with levothyroxine (LT 4 ) to achieve either a normal or low serum TSH concentration. All laboratory evaluations were repeated twice while patients were taking LT 4 . Thyroid hormone concentrations were documented by both immunoassay and LC-MS=MS, and their relationship with TSH was studied both in the entire group and in individual patients pre-and postthyroidectomy. Results: FT 4 and total T 3 correlated better with the log-transformed TSH when measured by LC-MS=MS. Postthyroidectomy the closest correlation was between log TSH and FT 4 (r ¼ 0.86, p < 0.001). The next best correlation was between log TSH and total T 3 (r ¼ 0.71, p < 0.001). When all data points were combined, the slope of the relationship between log TSH and total T 3 was relatively blunted compared with the log TSH-FT 4 slope (slope À 0.39 vs. À 1.38; p < 0.001), perhaps suggesting autoregulation of T 3 in response to the altered conditions postthyroidectomy. Conclusion: LC-MS=MS is an excellent tool for documenting the known physiological phenomenon of a loglinear relationship between TSH and thyroid hormone concentrations. In a group of patients studied pre-and postthyroidectomy, both FT 4 and total T 3 measured by tandem mass spectrometry correlate well with TSH. However, T 3 correlates slightly less well and has a relatively blunted relationship with the log-transformed TSH. These paired data suggest that in LT 4 -replaced patients T 3 concentrations are held stable in the face of fluctuating T 4 concentrations.

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Section: Thyroid Profilesmentioning

confidence: 99%

Tandem Mass Spectrometry as a Novel Tool for Elucidating Pituitary–Thyroid Relationships

Jonklaas

Soldin

2008

Thyroid

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“…The maximum FT4 concentration occurs approximately two hours after the drug ingestion [30]. Moreover, there is a transient increase of FT4 serum level after ingestion of L-T4 for 5 hours [31]. Since FT4 directly influences Hcy concentration, during this time Hcy metabolism is similar to hyperthyroid state and it may lead to decreased Hcy levels in treated HT patients in contrast to healthy controls, in whom FT4 output is adjusted to real needs and the rate of physiological elimination .…”

Section: Discussionmentioning

confidence: 99%

Serum homocysteine levels are decreased in levothyroxine-treated women with autoimmune thyroiditis

et al. 2014

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BackgroundHyperhomocysteinemia is a well-known cardiovascular risk factor and its elevation is established in overt hypothyroidism. Since some authors suggest that chronic autoimmune thyroiditis per se may be considered as a novel risk factor of atherosclerosis independent of thyroid function, the analysis of classical cardiovascular risk factors might be helpful in evaluation the causative relationship. Data concerning the impact of thyroid autoimmunity in euthyroid state on homocysteine (Hcy) level is lacking. The aim of this study was to evaluate Hcy level in context of anti-thyroperoxidase antibodies (TPOAbs) in euthyroidism.MethodsIt is a case–control study. 31 euthyroid women treated with levothyroxine (L-T4) due to Hashimoto thyroiditis (HT) and 26 females in euthyroidism without L-T4 replacement therapy were enrolled in the study. All women with HT had positive TPOAbs. Forty healthy females negative for TPOAbs comparable for age and body mass index (BMI) participated in the study as controls. Exclusion criteria were a history of any acute or chronic disease, use of any medications (including oral contraceptives and vitamin supplements), smoking, alcoholism.ResultsTPOAbs titers were higher in both groups of HT patients versus the healthy controls. Hcy levels were found to be significantly lower in treated HT patients (Me 11 μmol; IQR 4.2 μmol) as compared with healthy controls (Me 13.35 μmol; IQR 6.34 μmol; p = 0.0179). In contrast, no significant difference was found between non treated HT and control group in Hcy level. The study groups and the controls did not differ in age and BMI. Furthermore, levels of TSH, FT4, TC, LDL, HDL and TAG did not differ between the study group and the control group.ConclusionThe main finding of the study is a decrease in Hcy level in treated HT as compared with healthy controls. Based on our observations one can also assume that correct L-T4 replacement was associated here with a decrease of Hcy. Furthermore, it seems that non treated HT in euthyroidism is not associated with Hcy increase, in contrast to overt hypothyroidism. This may be just another argument against the concepts about the role of “euthyroid HT” in the development of atherosclerosis.

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“…In some of these studies, serum T4 concentrations appeared unexplainably elevated. 30 Others have documented that serum thyroxine levels were significantly elevated from trough levels at 2 to 9 hours from the time of dose ingestion, 31–34 producing increases in measured total and free thyroxine. It was argued that transient elevations in free and total T4 levels that occur over 9 hours are artifacts of hormone equilibration in the serum compartment and do not reflect steady-state values.…”

Section: Discussionmentioning

confidence: 99%

Longitudinal Comparison of Thyroxine Pharmacokinetics Between Pregnant and Nonpregnant Women: A Stable Isotope Study

Soldin¹,

Vinks²,

Younis³

et al. 2010

Therapeutic Drug Monitoring

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The treatment of maternal hypothyroidism presents clinicians with a unique challenge, because dosing regimens previously developed and validated for nonpregnant women cannot be easily extrapolated to dosing in pregnancy. Thyroid hormone requirement increases by 20% to 40% early during pregnancy, persisting throughout gestation. Accordingly, women with treated hypothyroidism need to increase their levothyroxine dose to prevent maternal hypothyroidism and the associated impaired cognitive development and increased fetal mortality. We investigated the pharmacokinetic properties of levothyroxine during pregnancy through the use of a novel, traceable form of levothyroxine. The objective was to conduct a longitudinal study to determine whether levothyroxine pharmacokinetics differ in the pregnant versus nonpregnant state. We used a unique 13C-levothyroxine-tracer method to distinguish between endogenous and exogenous levothyroxine and studied the pharmacokinetics of a single oral dose of levothyroxine using tandem mass spectrometry. Moreover, we were able to detect single dose amounts of the drug, in picogram/mL concentrations. The area under the curve was 23.0 ng*h/mL in pregnancy and 14.8 ng*h/mL in nonpregnant women (P < 0.03) with median serum half-lives of 32.1 hours and 24.1 hours, respectively (P < 0.04). Further research involves the measurement of free thyroxine on these samples using tandem mass spectrometry. Future work should focus on the mechanisms responsible for the gestational differences in pharmacokinetics and whether these should necessitate dose schedule changes in pregnancy.

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Thyroid Hormone Levels Affected by Time of Blood Sampling in Thyroxine-Treated Patients

Cited by 47 publications

References 17 publications

Tandem Mass Spectrometry as a Novel Tool for Elucidating Pituitary–Thyroid Relationships

Tandem Mass Spectrometry as a Novel Tool for Elucidating Pituitary–Thyroid Relationships

Serum homocysteine levels are decreased in levothyroxine-treated women with autoimmune thyroiditis

Longitudinal Comparison of Thyroxine Pharmacokinetics Between Pregnant and Nonpregnant Women: A Stable Isotope Study

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