This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood Physiology, Subject name: Physiology
Which of the following promotes rouleaux formation? 
Select and explain. 
A. Zeta potential on RBC membrane, B. Fibrinogen, C. Albumin, D. Biconcave shape of RBC
B: Fibrinogen
Answer: B: Fibrinogen 
Explanation: When in circulation, the negative charge on the RBC membrane (or zeta potential) does not allow RBCs to clump. When blood is made to stand in a veical tube, the asymmetric macromolecules in the plasma overcome the zeta potential, so as to form the rouleaux and settling down of the RBC clumps. Fibrinogen and gamma-globulins are the examples of such asymmetric macromolecules. Plasma albumin retards the rouleaux formation. Hence, in nephrotic syndrome, in which the albumin levels fall, there is a rise in ESR.