**Core Concept**
Transferrin saturation is a measure of iron overload or deficiency in the body. It represents the percentage of transferrin, a protein responsible for iron transport, that is bound to iron. This calculation is essential in diagnosing and managing iron-related disorders.

**Why the Correct Answer is Right**
Transferrin saturation is calculated by dividing the serum iron level by the total iron-binding capacity (TIBC) and multiplying the result by 100. This value helps clinicians assess the body's iron status. When transferrin saturation is high (above 45%), it indicates iron overload, whereas a low value (below 15%) suggests iron deficiency.

**Why Each Wrong Option is Incorrect**
**Option A:** This value is not a measure of transferrin saturation, but rather a related concept.
**Option B:** This is incorrect because transferrin saturation is not a direct measure of serum iron levels.
**Option C:** This option is incorrect as it refers to a different concept related to iron metabolism, not transferrin saturation.

**Clinical Pearl / High-Yield Fact**
Remember that transferrin saturation is a crucial parameter in diagnosing iron overload conditions, such as hemochromatosis, and iron deficiency anemia.

**Correct Answer: D. Serum iron level divided by total iron-binding capacity (TIBC) and multiplied by 100.**