Written by: Solaris Diagnostics

The thyroid  is part of the human endocrine system. The hormones secreted by the thyroid gland are considered Amines. The regulation of thyroid hormones is controlled by a negative feedback loop. A negative feedback loop simply means that when levels of hormones within the body are high, hormone production decreases, and visa versa. The thyroid secretes two hormones, thyroxine (T4) and triiodothyronine (T3) when stimulated to do so by TSH. T3 and T4 stimulate metabolic activity. They increase many body systems and allow for more brain activity, an increase in the movement of the gastrointestinal tract, an increase in heart rate and blood flow, increased oxygen consumption and increased heat production. In children, it also stimulates musculoskeletal and nervous system growth and development.

T4 is used to diagnose or determine severity of hyper- (overactive) or hypo- (underactive) thyroidism after obtaining an abnormal TSH result. 99.98% of thyroxine is bound to proteins. The 0.02% of unbound thyroxine is called “free” T4 and can be measured using an automated testing system. Normal, healthy adults typically have a free thyroxine level of 0.89-1.76 ng/mL.

T3 is used to diagnose hyperthyroidism. It is usually not measured until an abnormal TSH or T4 result is obtained. 99.7% of triiodothyronine is bound to proteins. The 0.3% of unbound triiodothyronine is called “free” T3 and can be measured using an automated testing system. Normal, healthy adults typically have a free triiodothyronine level of 2.30-4.20 pg/mL.

Solaris tests for these two values using chemiluminescent technology. Specimens are stable refrigerated at 2-8 °C for 4 days. If testing cannot be completed by then, freeze specimens at -20°C. Expected turnaround time for these assays is 24 hours after receiving in the laboratory.

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