Ferritin
Produced by: Nearly every cell in the body.
Definition / Purpose: Binds and transports iron throughout the body.  
Lab Reference Range: See Below
Men: 20 to 500 ng/mL. Women, 20 to 200 ng/mL.
When to order:

• Screening test that should be ordered when looking for hypothyroidism. Why? Two reasons: Symptoms of low ferritin can mimic hypothyroidism. And secondly, low ferritin may be affecting thyroid hormone synthesis by reducing the activity of the enzyme thyroid peroxidase, which is dependent on iron. Iron deficiency may also alter thyroid metabolism and reduce the conversion of T4 to T3

Pearls:

• Half-life: 72 hours
• Usually for a properly functioning thyroid gland you want a ferritin level between 50 and 100 ng/mL.
• Two common causes of low ferritin are heavy periods and low acid production in the stomach (hypochlorhydria) secondary to GERD or heartburn medications. Stomach acid is needed for the absorption of iron.
• Ferritin is an indirect marker for the amount of iron that is stored in the body.