Vitamins, Minerals and Iron

Transferrin Saturation

Also written as: TSAT, Iron saturation

The share of the blood's iron-carrying capacity that is actually filled with iron.

What it measures

A calculated value rather than a separate blood draw. It compares serum iron with the total iron-binding capacity to show what fraction of the carrier protein transferrin is actually loaded with iron.

Why a doctor orders it

A key part of the iron panel, ordered when either iron deficiency or iron overload is being assessed. It is the usual first screening value when hereditary iron overload, known as hemochromatosis, is being considered.

What is generally associated with a higher result

Broadly associated with iron overload states and with recent iron supplementation. Because it is calculated from serum iron, it inherits that test's large hour-to-hour and day-to-day swings.

What is generally associated with a lower result

Broadly associated with iron deficiency, and with inflammation or chronic illness, both of which reduce the amount of iron circulating in blood.

Everyday things that move this number

Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:

• Time of day, because serum iron peaks in the morning
• Iron supplements or a recent iron-rich meal
• Whether the sample was taken fasting
• Recent illness or inflammation

Questions to take to your appointment

• Was this a fasting morning sample, and does that matter for the result?
• How does it compare with the ferritin from the same panel?
• If it stayed raised on repeat testing, would genetic testing for hemochromatosis ever be considered?

Build a printable questionnaire with your own results →

Where to read more

MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .

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