Thyroid Testing

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THYROXINE (T4)

Thyroxine is the thyroid hormone that contains four atoms of iodine. It is used to evaluate thyroid function. It is the direct measurement of total T4 concentration in the blood serum. Increased levels are found in hyperthyroidism, acute thyroiditis, and hepatitis. Low levels can be found in Cretinism, hypothyroidism, cirrhosis, malnutrition, and chronic thyroiditis.

Reference Adult Range: 4 – 12 ug/dl
Optimal Adult Reading: 8 ug/dl

T3-UPTAKE

This test is an indirect measurement of unsaturated thyroxine binding globulin in the blood. Increased levels are found in hyperthyroidism, severe liver disease, metastatic malignancy, and pulmonary insufficiency. Decreased levels are found in hypothyroidism, normal pregnancy, and hyperestrogenis status.

Reference Adult Range: 27 – 47%
Optimal Adult Reading: 37 %

FREE T4 INDEX (T7)

This index is a calculation used to correct the estimated total thyroxine for the amount of thyroxine binding globulin present. It uses the T4 value and the T3 uptake ratio.

Reference Adult Range: 4 – 12
Optimal Adult Reading: 8

THYROID-STIMULATING HORMONE (TSH)

TSH, produced by the anterior pituitary gland, causes the release and distribution of stored thyroid hormones. When T4 and T3 are too high, TSH secretion decreases, when T4 and T3 are low, TSH secretion increases.

Reference Adult Range: .5 – 6 miliIU/L
Optimal Adult Reading: 3.25 miliU/L