This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Beta-2 transferrin is found in ? 
Select and explain. 
A. Blood, B. Urine, C. Tear, D. CSF
D: CSF
Answer: D: CSF 
Explanation: Ans. is 'd' i.e., CSFBeta-2 transferrin is an isoform of transferrin.It is found in cerebrospinal fluid (CSF).It is not found in other body fluids (blood, mucus, tear, saliva, urine).Therefore, it is a specific marker for CSF and is used for diagnostic of CSF leaks.