Thyroid function tests serum thyroxine

After treatment is initiated, patients should be examined and thyroid function tests (serum-free thyroxine index and total triiodothyronine concentrations) measured every 2 to 4 months. Once euthyroidism is established, follow-up every 4 to 6 months is reasonable. 

Thyroid function tests - Decreased levels of thyroxine-binding globulin, resulting in decreased total T4 serum levels and increased resin uptake of T3 and T4. Free thyroid hormone levels remain unchanged, and there is no... 

Thyroid function tests are often altered by somatropin because of increased conversion of T4 to T3, but this is clinically insignificant at low doses (SEDA-21, 453). One child with Prader-Willi syndrome had a fall in serum thyroxine concentration during somatropin therapy and needed thyroxine replacement (33). Hypothyroidism developed in 11 of 46 growth hormone-deficient children treated with somatropin (34). Prior abnormalities in hypothalamic-pituitary function and alterations in thyroid hormone metabolism, probably both, contributed to the high incidence of hypothyroidism, which was similar to that in previous studies. 

A 72-year-old woman with dilated cardiomyopathy was given amiodarone for fast atrial flutter and 6 months later developed abnormal thyroid function tests, with a suppressed TSH and a raised serum thyroxine. The autoantibody profile was negative and a thyroid uptake scan showed reduced uptake (44). 

Artefactual increases of as much as 50% in total thyroxine, estimated by a competitive protein-binding assay, and of as much as 30% in triiodothyronine resin uptake are probably due to rapid and continuing lipolytic hydrolysis of triglycerides after blood has been drawn (126). Thyroid function tests should therefore always be performed on blood samples taken before (or a sufficient time after) heparin treatment (127). An increase in serum-free thyroxine concentrations has also been reported after low molecular weight heparin, by up to 171% in specimens taken 2-6 hours after injection. When specimens were obtained 10 hours after injection, the effects were smaller, but with concentrations still up to 40% above normal the results can still cause errors of interpretation (128). 

Thyroid function tests typically run a triphasic course. Initially, serum thyroxine levels are elevated owing to release of preformed thyroid hormone from disrupted follicles. The 24-hour RAIU during this time is less than 2% owing to thyroid inflammation and TSH suppression by the elevated thyroxine level. As the disease progresses, intrathyroidal hormone stores are depleted and the patient may become mildly hypothyroid with an appropriately elevated TSH level. During the recovery phase thyroid hormone stores are replenished and serum TSH elevation gradually returns to normal. Recovery is generally complete within 2 to 6 months. Most patients remain euthyroid and recurrences of painful thyroiditis are extremely rare. The patient with painful thyroiditis should be reassured that the disease is self-limited and is unlikely to recur. Thyrotoxic symptoms may be relieved with /3-blockers. Aspirin (650 mg orally every 6 hours)... 

B. This patient appears to have a hyperthyroid condition even though the thyroid does not appear to be enlarged. Thyroid function tests would be most helpful to determine if this is the case. The free thyroxine level is a direct measure of the amount of free T, the biologically active T, in the serum. Elevation of the free T indicates a hyperthyroid condition. 

Thyroid function test Thyroxine Triodo thyronine Thyroid-stimulating hormone Serum or plasma nmoll nmoll ui- No Thyroid function... 

The determination of the levels of thyroxine (T4) and TSH in serum may be used to indicate thyroid function, thus providing an indirect measurement of iodine sufficiency. However, although serum T4 and TSH levels can be accurately and precisely measured, the tests tend to be costly and technically time-consuming. In comparison, measurements of urinary iodine excretion are cheaper and technically simpler, with no requirement to take a blood sample. 

---