The substance that is present in both serum and plasma is
**Core Concept**
The question is testing the understanding of the difference between serum and plasma, which is a fundamental concept in clinical biochemistry. Serum and plasma are both blood components, but they differ in the presence or absence of clotting factors.
**Why the Correct Answer is Right**
Plasma is the liquid portion of blood that separates from the cells when blood is centrifuged. It contains all the clotting factors, proteins, and other substances that are present in the blood. Serum, on the other hand, is plasma that has been allowed to clot, and the clotting factors have been removed. Therefore, the only substance that is present in both serum and plasma is fibrinogen, which is a clotting factor that is present in plasma but absent in serum after clotting.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** This option is not provided.
* **Option C:** This option is not provided.
**Clinical Pearl / High-Yield Fact**
Fibrinogen is a critical clotting factor that helps to form a fibrin clot in the event of bleeding. It is also a useful marker for liver function, as it is synthesized in the liver.
**Correct Answer: B. Fibrinogen. Fibrinogen is the substance that is present in both serum and plasma.**