title: 3,3'-Diiodothyronine concentrations in hospitalized or thyroidectomized patients: results from a pilot study.
abstract: OBJECTIVE
  To determine if various medical conditions affect the serum concentrations of 3,3'-diiodothyronine (3,3'-T2).
  
  
  METHODS
  A total of 100 patients who were recruited from a group of inpatients and outpatients with a diverse range of medical conditions, donated a single blood sample that was assayed for thyroid hormone derivatives using liquid-chromatography tandem mass spectrometry (LC-MS/MS). The associations between 3,3'-T2 concentrations and physiologic data and medical conditions were assessed.
  
  
  RESULTS
  Higher quartiles of 3,3'-T2 concentrations (quartile 1: 2.01-7.48, quartile 2: 7.74-12.4, quartile 3: 12.5-17, quartile 4: 17.9-45.8 pg/mL) were associated with decreasing occurrence of critical illness (58%, 11%, 0%, 8%), stroke (29%, 7.7%, 4%, 0%), critical care unit hospitalization (75%, 39%, 8.3 %, 12%), and inpatient status (83%, 42%, 8%, 12%) (all P<.001). The same quartiles were associated with increasing frequency of thyroidectomy (4%, 12%, 17%, 60%). In multivariate analyses, after adjustment for age and sex, inpatient status was associated with decreasing concentrations of 3,3'-T2 (46% decrease for inpatients with 95% confidence interval [CI] 32-57%, P<.0001). Thyroidectomy was associated with increasing concentrations of 3,3'-T2 (29% increase (CI 0.5-66%, P = .049).
  
  
  CONCLUSIONS
  We observed associations between inpatient status and reduced 3,3'-T2 concentrations. This appears to be a global change associated with illness, rather than an association with specific medical conditions. We also observed higher 3,3'-T2 concentrations in athyreotic outpatients receiving thyroid-stimulating hormone (TSH) suppression therapy. This demonstrates that there is production of 3,3'-T2 from levothyroxine (LT4) in extrathyroidal tissues. Conversion of thyroxine (T4) to 3,3'-T2 via both triiodothyronine (T3) and reverse triiodothyronine (rT3) pathways may prevent excessive T3 concentrations in such patients.
authors: Division of Endocrinology, Georgetown University, Washington DC.
authors: Jacqueline
authors: J
authors: Jonklaas
authors: Division of Endocrinology, Georgetown University, Washington DC Section of Endocrinology, Medstar Washington Hospital Center.
authors: Anpalakan
authors: A
authors: Sathasivam
authors: Medstar Health Research Institute, Hyattsville, Maryland.
authors: Hong
authors: H
authors: Wang
authors: Division of Endocrinology, Georgetown University, Washington DC.
authors: David
authors: D
authors: Finigan
authors: Division of Endocrinology, Georgetown University, Washington DC Department of Oncology, National Institutes of Health, Bethesda, Maryland.
authors: Offie P
authors: OP
authors: Soldin
authors: Section of Endocrinology, Medstar Washington Hospital Center.
authors: Kenneth D
authors: KD
authors: Burman
authors: Division of Endocrinology, Georgetown University, Washington DC Department of Laboratory Medicine, National Institutes of Health, Bethesda, Maryland.
authors: Steven J
authors: SJ
authors: Soldin
mesh_terms: D000328:Adult; D000368:Aged; D004104:Diiodothyronines / Q000097:blood*; D005260:Female; D006760:Hospitalization; D006801:Humans; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D053719:Tandem Mass Spectrometry; D013965:Thyroidectomy; D014284:Triiodothyronine / Q000097:blood
chemical_list: D004104:Diiodothyronines; D014284:Triiodothyronine; C030629:3,3'-diiodothyronine