The thyroid stimulating hormone (TSH) is produced and secreted by the pituitary gland and stimulates the thyroid to produce T3 and T4. When TSH is elevated, low thyroid function may be indicated. If TSH is low it is indicative of high thyroid function. A study found that TSH was suppressed in all subjects after food, so fasting may be suggested although it is not reqired by Quest. Free T4 and Free T4 values did not change significantly after eating.

T3 or triiodothyronine is the active form of the thyroid hormone. T3 acts as a metabolic throttle for fueling all of the daily cellular functions. Free T3 is the unbound portion of T3 that is biologically active.

Elevated levels of homocysteine in the blood, known as hyperhomocysteinemia, have been linked to an increased risk of cardiovascular disease, including heart attack and stroke. High homocysteine levels may also be associated with an increased risk of certain other health conditions, such as osteoporosis and pregnancy complications.

Insulin-like Growth Factor 1, also known as IGF-1, is used as a biomarker for blood levels of human growth hormone. It is a hormone produced by the liver and other tissues which affects growth-promoting activities and glucose metabolism. The blood level of IGF-1 appears to fluctuate over 24 hours and is found to be related to growth hormone secretion.

SHBG (sex hormone binding globulin) binds to testosterone and estradiol. High SHBG may decrease free testosterone and free estradiol.

A single fasting growth hormone (GH) level is of limited value. The secretion of GH is episodic and pulsatile. GH has a half-life of 20 to 25 minutes. Testing for growth hormone deficiency or excess is best done as part of a dynamic test involving specific stimuli (see the online Endocrine Appendices: Growth Hormone Stimulation and Growth Hormone Suppression). Insulin-like growth factor-1 can also be useful in assessing growth hormone status.

Ferritin is a protein that stores iron. Red blood cells need iron to form normally and carry oxygen around your body. Low levels of ferritin lead to iron deficiency anemia, which means you have too few red blood cells. High levels of ferritin can damage your joints, heart, liver, and pancreas.