Serum is the fluid in which your blood cells, platelets and any other solids are suspend after clotting has taken place. Before clotting has occurred the fluid in which your blood cells are suspended is called plasma. The blood for the serology assay is drawn into a tube that does not contain anticoagulant additives and allowed to clot. It is then centrifuged and the cells and other solids go to the bottom of the tube and a separating jell moves between the solids and the serum to prevent the cells from remixing with the serum. The serology test is looking for antibodies that your immune system makes in response to infection. The antibodies to each infection are peculiar to that infection. One potential problem with looking for antibodies to an infectious agent which happens to attack your immune system is that if you have been infected for a long time and your immune system is so shot that it is no longer able to mount a decent antibody response to the infection, you might conceivably be negative by serological antibody assay but still actually have the virus. I do not know if this happens in people with XMRV or its related viruses. It's theoretically possible. Maybe someone who knows the answer would enlighten us. It is curious that results of the culture are reportable before the serology results, since the serology assay takes much less time to perform because the culture has to be grown first, but for serology, no extra time is needed. Perhaps it's simply a backlog problem. Maybe they are flooded with serology samples since it has just become available and it's much less expensive and (theoretically) faster. I hope this is not an indication that there is a problem with their new serology assay. I sent in my blood for the serology test on 8/30/10 and they received it on 8/31/10. I am very interested in when you get your results for the serology, Sushi, because I would expect mine around the same time.