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Triiodothyronine levels in athyreotic individuals during levothyroxine therapy.
JAMA 2008; 299(7):769-77JAMA

Abstract

CONTEXT

Thyroidal production of triiodothyronine (T3) is absent in athyreotic patients, leading to the suggestion that T3 deficiency may be unavoidable during levothyroxine (LT4) therapy. However, trials evaluating therapy with combined LT4 and T3 have failed to demonstrate any consistent advantage of combination therapy.

OBJECTIVE

To determine whether T3 levels in patients treated with LT4 therapy were truly lower than in the same patients with native thyroid function.

DESIGN, SETTING, AND PATIENTS

A prospective study conducted in the General Clinical Research Center, Georgetown University Medical Center, Washington, DC, between January 30, 2004, and June 20, 2007, of 50 euthyroid study participants aged 18 to 65 years who were scheduled for total thyroidectomy for goiter, benign nodular disease, suspected thyroid cancer, or known thyroid cancer. Following thyroidectomy, patients were prescribed LT4. Patients with benign thyroid disease and thyroid cancer were treated to achieve a normal and suppressed serum thyroid-stimulating hormone (TSH) level, respectively. The LT4 dose was adjusted as necessary postoperatively to achieve the desired TSH goal.

MAIN OUTCOME MEASURE

Thyroxine (tetraiodothyronine [T4]), T3, and TSH levels were measured twice preoperatively and twice postoperatively.

RESULTS

By the end of the study, there were no significant decreases in T3 concentrations in patients receiving LT4 therapy compared with their prethyroidectomy T3 levels (mean, 127.2 ng/dL; 95% confidence interval [CI], 119.5-134.9 ng/dL vs 129.3 ng/dL; 95% CI, 121.9-136.7 ng/dL; P = .64). However, free T4 concentrations were significantly higher in patients treated with LT(4) therapy (mean, 1.41 ng/dL; 95% CI, 1.33-1.49 ng/dL) compared with their native free T4 levels (1.05 ng/dL; 95% CI, 1.00-1.10 ng/dL; P < .001). Serum TSH values of 4.5 mIU/L or less were achieved in 94% of patients by the end of the study. The T3 concentrations were lower in the subgroup of patients whose therapy had not resulted in a TSH level of 4.5 mIU/L or less (P < .001).

CONCLUSION

In our study, normal T3 levels were achieved with traditional LT4 therapy alone in patients who had undergone near-total or total thyroidectomy, which suggests that T3 administration is not necessary to maintain serum T3 values at their endogenous prethyroidectomy levels.

Authors+Show Affiliations

Division of Endocrinology, Georgetown University Medical Center, Washington, DC, USA. jj@bc.georgetown.eduNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Comparative Study
Journal Article
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

18285588

Citation

Jonklaas, Jacqueline, et al. "Triiodothyronine Levels in Athyreotic Individuals During Levothyroxine Therapy." JAMA, vol. 299, no. 7, 2008, pp. 769-77.
Jonklaas J, Davidson B, Bhagat S, et al. Triiodothyronine levels in athyreotic individuals during levothyroxine therapy. JAMA. 2008;299(7):769-77.
Jonklaas, J., Davidson, B., Bhagat, S., & Soldin, S. J. (2008). Triiodothyronine levels in athyreotic individuals during levothyroxine therapy. JAMA, 299(7), pp. 769-77. doi:10.1001/jama.299.7.769.
Jonklaas J, et al. Triiodothyronine Levels in Athyreotic Individuals During Levothyroxine Therapy. JAMA. 2008 Feb 20;299(7):769-77. PubMed PMID: 18285588.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Triiodothyronine levels in athyreotic individuals during levothyroxine therapy. AU - Jonklaas,Jacqueline, AU - Davidson,Bruce, AU - Bhagat,Supna, AU - Soldin,Steven J, PY - 2008/2/21/pubmed PY - 2008/2/26/medline PY - 2008/2/21/entrez SP - 769 EP - 77 JF - JAMA JO - JAMA VL - 299 IS - 7 N2 - CONTEXT: Thyroidal production of triiodothyronine (T3) is absent in athyreotic patients, leading to the suggestion that T3 deficiency may be unavoidable during levothyroxine (LT4) therapy. However, trials evaluating therapy with combined LT4 and T3 have failed to demonstrate any consistent advantage of combination therapy. OBJECTIVE: To determine whether T3 levels in patients treated with LT4 therapy were truly lower than in the same patients with native thyroid function. DESIGN, SETTING, AND PATIENTS: A prospective study conducted in the General Clinical Research Center, Georgetown University Medical Center, Washington, DC, between January 30, 2004, and June 20, 2007, of 50 euthyroid study participants aged 18 to 65 years who were scheduled for total thyroidectomy for goiter, benign nodular disease, suspected thyroid cancer, or known thyroid cancer. Following thyroidectomy, patients were prescribed LT4. Patients with benign thyroid disease and thyroid cancer were treated to achieve a normal and suppressed serum thyroid-stimulating hormone (TSH) level, respectively. The LT4 dose was adjusted as necessary postoperatively to achieve the desired TSH goal. MAIN OUTCOME MEASURE: Thyroxine (tetraiodothyronine [T4]), T3, and TSH levels were measured twice preoperatively and twice postoperatively. RESULTS: By the end of the study, there were no significant decreases in T3 concentrations in patients receiving LT4 therapy compared with their prethyroidectomy T3 levels (mean, 127.2 ng/dL; 95% confidence interval [CI], 119.5-134.9 ng/dL vs 129.3 ng/dL; 95% CI, 121.9-136.7 ng/dL; P = .64). However, free T4 concentrations were significantly higher in patients treated with LT(4) therapy (mean, 1.41 ng/dL; 95% CI, 1.33-1.49 ng/dL) compared with their native free T4 levels (1.05 ng/dL; 95% CI, 1.00-1.10 ng/dL; P < .001). Serum TSH values of 4.5 mIU/L or less were achieved in 94% of patients by the end of the study. The T3 concentrations were lower in the subgroup of patients whose therapy had not resulted in a TSH level of 4.5 mIU/L or less (P < .001). CONCLUSION: In our study, normal T3 levels were achieved with traditional LT4 therapy alone in patients who had undergone near-total or total thyroidectomy, which suggests that T3 administration is not necessary to maintain serum T3 values at their endogenous prethyroidectomy levels. SN - 1538-3598 UR - https://www.unboundmedicine.com/medline/citation/18285588/Triiodothyronine_levels_in_athyreotic_individuals_during_levothyroxine_therapy_ L2 - https://jamanetwork.com/journals/jama/fullarticle/10.1001/jama.299.7.769 DB - PRIME DP - Unbound Medicine ER -