For most organs, the only way to show unequivocally that rejection is occurring is by biopsy of that organ. For practical reason, however, biopsies are not always done when acute rejection is suspected. In some circumstances treatment for rejection is begun and a biopsy is performed at a later date if the organ doesn't seem to be improving. This strategy varies from organ to organ and transplant center to transplant center. The diagnosis and treatment of acute rejection can be extremely difficult at times.
Chronic rejection is less well defined than either hyperacute or acute rejection.
The definitive diagnosis of chronic rejection is again generally made by biopsy of the organ in question. Livers with chronic rejection have a decreased number of bile ducts on biopsy. To date, most research has focused on graft survival for the first three years. It is not that we, the physicians involved with transplantation, don't care about long term results. The long term problem is simply tough to tackle.