What are the disadvantages of using RBCs as carrier molecules in the passive Hemagglutination test?

1-The frequent Presence of natural Heterophile Ab to the RBCs in tested serum. It can produce false agglutination.

2-The natural presence of Complement proteins in serum: This complement if reacted with the Ag-Ab complex it causes lysis of the RBCs.

3-The Short durability of the carrier RBCs: Fresh red blood cells, whether coated or not, can only be used for a limited time (few weeks) before they become fragile, infected and excessively haemolysed.