Thyroid Testing Cascade

Mary E. Tang, M.D. March 1998

Listed below is a chart for Thyroid Testing Cascade for the evaluation of primary thyroid dysfunction. This test cascade will allow clinicians to use reflex ordering of thyroid function tests in order to provide more timely and cost effective laboratory diagnosis of common thyroid function disorders. This test cascade is only intended for ambulatory patients and is not recommended for inpatients, patients with pituitary or hypothalamic disorders or patients with acute illness or neuropsychiatric disease. The cascade is performed only if the physician specifically orders it. Patients are charged only for the tests that are performed. Monitoring thyroid hormone replacement can be done with TSH alone and does not require the test cascade.

The basis for the cascade is the TSH. Recent improvements in testing have made TSH the most sensitive indicator of primary hyper/hypothyroidism. A normal TSH effectively excludes primary thyroid dysfunction. It is not sensitive for cases in which pituitary or hypothalamic etiologies are suspected. In those cases a TSH and free T4 should be ordered.

The Thyroid Test Cascade starts with a TSH. If the TSH result is abnormal a free T4 is performed. In cases where a TSH is suppressed and the free T4 is low or normal a total T3 is done to test for T3 toxicosis.

When the Thyroid Test Cascade is ordered a report will follow showing the tests performed and the results. There is no accompanying interpretative report. Interpretation is available through your local pathologist.

Dr. Mary Tang is a Clinical Pathologist in Burlington, Vermont. Questions about this protocol may be directed to Dr. Tang at 802-847-5121 or 800-991-2799.

This protocol is a joint initiative of NECLA and the VSPS