Test Code SAT Percent Saturation
Specimen Required
Only orderable as part of profile. For more information see SFEC / Iron and Total Iron-Binding Capacity, Serum
Secondary ID
2503Useful For
Calculation of percent saturation
Method Name
Only orderable as part of profile. For more information see SFEC / Iron and Total Iron-Binding Capacity, Serum
Calculation
Reporting Name
Percent SaturationSpecimen Type
SerumSpecimen Stability Information
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Serum | Refrigerated (preferred) | 21 days | |
Frozen | 365 days |
Clinical Information
Transferrin is the plasma iron transport protein, which binds iron strongly to keep iron nonreactive in circulation and deliver it to cells with transferrin receptors. The rate of transferrin synthesis in the liver can be altered according to the body’s iron requirements and iron reserves. The circulating concentration increases in response to iron deficiency and decreases in response to iron overload. Transferrin is generally only 25% to 30% saturated with iron. Total iron binding capacity (TIBC) is estimated from transferrin concentration using the molecular weight of the transferrin, accounting for each transferrin molecule that can bind 2 atoms of iron.
Iron deficiency, iron overload, and anemia of chronic disease are the most prevalent disorders of iron metabolism. Serum iron, TIBC, and percent saturation are widely used for the diagnosis of iron deficiency and iron overload, such as hemochromatosis. Iron concentration and percent saturation decrease with iron deficiency and increase when iron is in excess. Serum ferritin is a much more sensitive and reliable test for demonstration of iron deficiency.
Anemia of chronic disease is often observed in patients with autoimmune diseases, chronic kidney diseases, inflammatory bowel disease, and chronic heart failure. It is diagnosed when serum iron concentrations are low despite normal serum ferritin concentrations indicating adequate iron stores. However, in the presence of inflammation, ferritin can mask iron deficiency; therefore, measuring soluble transferrin receptors is suggested.
The biologic variation of iron and, therefore, iron saturation is notable in normal healthy persons and in various clinical disorders owing to both diurnal variation and post-prandial effects. The intraindividual day-to-day variation of iron and iron saturation is approximately 25% to 30%.(1) Recommendations on blood sampling for iron and iron saturation measurements are contradictory; however, minimizing influence of these effects can be accomplished by collecting during the morning after an overnight fast.
Reference Values
Only orderable as part of profile. For more information see SFEC / Iron and Total Iron-Binding Capacity, Serum
14-50%
Interpretation
Percent saturation often exceeds 45% in hereditary hemochromatosis and 90% in advanced iron overload states.(2)
Percent saturation less than 16% is generally used to screen for iron deficiency, but a threshold of 20% is used in the presence of inflammation.(3)
Cautions
Serum iron, total iron-binding capacity, and percent saturation are widely used for the diagnosis of iron deficiency. However, serum ferritin is a much more sensitive and reliable test for demonstration of iron deficiency.
Measurement of serum iron, iron binding capacity, and percent saturation should not be used as the primary test for iron deficiency. It may be helpful in conjunction with ferritin and soluble transferrin receptor, especially in patients with inflammation.
Clinical Reference
1. Swinkels DW. Iron metabolism. In: Rifai N, Chiu RWK, Young I, Burnham CAD, Wittwer CT, eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier. 2023:chap 40
2. Kowdley KV, Brown KE, Ahn J, Sundaram V. ACG Clinical Guideline: Hereditary Hemochromatosis [published correction appears in Am J Gastroenterol. 2019 Dec;114(12):1927. doi:10.14309/ajg.0000000000000469]. Am J Gastroenterol. 2019;114(8):1202-1218. doi:10.14309/ajg.0000000000000315
3. Lopez A, Cacoub P, Macdougall IC, Peyrin-Biroulet L. Iron deficiency anaemia. Lancet. 2016;387(10021):907-916. doi:10.1016/S0140-6736(15)60865-0
Method Description
This test calculates the percentage of iron saturation using results obtained from the serum iron measurement and calculated total iron binding capacity (TIBC). The following calculation is performed in the laboratory information system:
Percent saturation = (Iron [mcg/dL]/TIBC [mcg/dL]) x100
Day(s) Performed
Monday through Sunday
Report Available
Same day/1 to 2 daysSpecimen Retention Time
7 daysPerforming Laboratory
Mayo Clinic Laboratories in RochesterTest Classification
This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.LOINC Code Information
Result ID | Test Result Name | Result LOINC Value |
---|---|---|
SAT | Percent Saturation | 2502-3 |