Improvement of laboratory diagnostics in hypothyroid patients using levothyroxine.

Recruitment & Eligibility

Status: Recruiting

Sex: Not specified

Target Recruitment: 500

Inclusion Criteria

Hypothyroid patients
- Ability to provide informed consent;
- Ability to speak and understand Dutch or English
- Intake of a stable dose of levothyroxine, meaning the dosage of levothyroxine
must not be changed during the appointment at the outpatient clinic
- Diagnosis of one of these forms of hypothyroidism
O Patients with primary hypothyroidism: euthyroid based on TSH according to
physician
O Patients with hypothyroidism after a total thyroidectomy due to thyroid
carcinoma (therefore athyroid): on target TSH according to physician (target
TSH depending on stage/severity of carcinoma)
O Patients using L-T4 due to therapy of Graves* disease: euthyroid based on TSH
according to physician (TSH cannot be suppressed, namely TSH within reference
interval of 0,5-5,0 mU/L)
O Patients with central hypothyroidism: euthyroid based on fT4 according to
physician (common is fT4 in the upper limit, reference interval is 12-22 pmol/L)

Healthy controls
- Ability to provide informed consent;
- Ability to speak and understand Dutch or English
- Consider themselves healthy

Exclusion Criteria

Hypothyroid patients
- Not euthyroid according to physician
- Pregnant
- Patients using L-T4 due to the treatment of Graves* disease: if TSH is still
suppressed
- Any of the following medication
o Iodide
o Liothyronine (Cytomel)
o Oral anticonceptiva
o Active treatment of malignancy (except DTC)

Healthy controls
- Pregnancy
- Any of the following medication
o Thyroid medication (a.o. levothyroxine, thiamazol, PTU)
o Lithium
o Amiodarone
o Propranolol
o Iodide
o Glucocorticoids
o Oral contraceptives
o Heparin
o Growth hormone
o Active treatment of malignancy

Study & Design

Study Type: Observational invasive

Study Design: Not specified

Primary Outcome Measures

Name	Time	Method
<p>fT3, fT3/fT4 ratio and fT4 and TSH concentrations.</p><br>

Secondary Outcome Measures

Name	Time	Method
<p>- Laboratory tests: rT3, TT4, TT3, SHBG, acylcarnitine profile, tyrosine,<br />phenylalanine, serine and DIO1/2/3 polymorphisms<br />- Questionnaire: ThyPRO-39</p>