Thyroid function tests and their interpretations
- 1. S U B C L I N I C A L H Y P O T H Y R O I D I S M S E C O N D A R Y H Y P O T H Y R O I D I S M E U T H Y R O I D S I C K S Y N D R O M E Thyroid Function Tests
- 2. Tests • T3: Total and Free • T4: Total and Free • TSH • Thyroglobulin ( Tg ) • Anti Thyroglobulin Antibody ( Anti-Tg ) • Thyroid Peroxidase Antibody ( TPO ) • TSH receptor antibody ( Anti-TSHR )
- 3. TSH T4 T3 INTERPRETATION Thyroid Hormones
- 4. Marker Normal level Increased level Decreased level Anti-TSHR No thyroid autoimmune disease Graves disease -- Anti-TPO Anti-Tg DO Hashimoto’s thyroiditis -- Thyroglobulin ( Tg ) Benign or malignant thyroid disease Goiter Graves disease Thyroid drug treatment Thyroid Antibodies
- 7. Subclinical Hypothyroidism By definition, subclinical hypothyroidism refers to biochemical evidence of thyroid hormone deficiency in patients who have few or no apparent clinical features of hypothyroidism.
- 8. Treatment Important to confirm that any elevation of TSH is sustained over a 3-month period before treatment is given. Do not recommend routine treatment when TSH levels are below 10 mU/L. Starting with a low dose of levothyroxine (25–50 g/d) with the goal of normalizing TSH. If thyroxine is not given, thyroid function should be evaluated annually.
- 9. Secondary Hypothyroidism Pituitary hypothyroidism is characterized by low basal TSH levels in the setting of low free thyroid hormone. It is rarely isolated. In contrast, patients with hypothyroidism of hypothalamic origin (presumably due to a lack of endogenous TRH) may exhibit normal or even slightly elevated TSH levels.
- 10. Causes Pituitary macroadenomas Iatrogenic causes: Pituitary surgery or Irradiation Genetic defects Hemorrhage, pituitary-apoplexy, subarachnoid hemorrhage. Ischemic – post-partum pituitary necrosis, shock. Aneurysm. Transient central hypothyroidism: Sick euthyroid syndrome or Over-replacement of T4 in primary hypothyroidism
- 11. Clinical features Features: mimic those seen with primary hypothyroidism but are generally less severe.
- 12. Laboratory Evaluation An inappropriately low serum TSH concentration in the presence of subnormal serum T4 and T3concentrations is characteristic of central hypothyroidism. TRH (200 g) injected intravenously causes a two- to threefold increase in TSH (and PRL) levels within 30 min. Anti-thyroid antibodies are invariably negative.
- 13. TRH-stimulation test Dynamic Testing. Serum TSH is measured serially post-TRH at 20 and 60 mts. Normal response: 20 mts TSH value higher than 60 mts TSH. A Flat response: seen in pituitary disease Delayed response: with the 60-mt value higher than the 20-mt value, as seen in hypothalamic disease.
- 14. Neuroimaging Magnetic Resonance Imaging of the pituitary gland Computed tomography
- 15. Treatment TRH and TSH administration seem ideal,although most are treated with Levothyroxine. Therapy should be monitored at 4- to 6-week intervals during the first 6 months, at 2- to 3-month intervals between ages 6 and 24 months and at 3- to 6-month intervals thereafter. If the initial diagnosis cannot be established definitively, levothyroxine can be withdrawn for 30 days at age 2–3 years without compromising brain maturation to allow reassessment.
- 16. Monitoring Monitoring needs to be frequent, initially at 1-2- monthly intervals, requiring: Ft4 to be in the upper half of the reference range and Improvement of clinical parameters while on T4 replacement, such as symptoms and heart rate response.
- 17. Sick Euthyroid Syndrome Any acute or chronic severe illness causing abnormalities in circulating TSH or thyroid hormone levels in the absence of underlying thyroid disease. Reduced T4 ->T3 conversion but normal/increased rT3.
- 18. Thank you!