LabCorp Test

Thyroxine Free Direct (T4) plus Thyroid-stimulating Hormone (TSH) Blood Test Panel

Quick Overview

Includes Free T4 and TSH.

Test #901


Availability: In stock


No fasting required.  Stop biotin consumption at least 72 hours prior to the collection.  Collection should not occur during or after administration of heparin.

Test Results 1-2 days. May take longer based on weather, holiday or lab delays.

T4 Free is the active form of thyroxine and is thought to be a more accurate reflection of thyroid hormone function. The free T4 test is thought by many to be a more accurate reflection of thyroid hormone function and, in most cases, its use has replaced that of the total T4 test. A total T4 or free T4 test is primarily ordered in response to an abnormal TSH test result. Sometimes the T4 will be ordered along with a TSH to give the doctor a more complete evaluation of the adequacy of the thyroid hormone feedback system. These tests are usually ordered when a person has symptoms of hyperthroidism or hypothyroidism.

Thyroid-stimulating Hormone (TSH) is used to diagnose a thyroid disorder in someone with symptoms, monitor thyroid replacement therapy in people with hypothyroidism, diagnose and monitor female infertility problems, help evaluate the function of the pituitary gland (occasionally), and screen adults for thyroid disorders, though expert opinions vary on the benefits of screening and at what age to begin.

TSH is a thyroid function test. Results are investigation of low thyroxine (T4); the differential diagnosis of primary hypothyroidism from normal, and the differential diagnosis of primary hypothyroidism from pituitary/hypothalamic hypothyroidism. TSH is high in primary hypothyroidism. Low TSH occurs in hyperthyroidism. Evaluation of therapy in hypothyroid patients receiving various thyroid hormone preparations: Low values are found in states of excessive thyroid replacement. Normal result on a sensitive TSH assay is acceptable evidence of adequate thyroid replacement.

This third-generation TSH assay can be considered a test for thyroid disease. A result within the accepted reference interval provides strong evidence for euthyroidism, a normally functioning thyroid.

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