Immunohistochemistry (IHC) - C4D Test

Immunohistochemistry (IHC)-C4D test

It is a laboratory test used for detection of antibody –mediated rejection (AMR) of transplanted kidneys in patients with kidney transplantation. This test is called IHC C4D test.

Kidney transplantation is a procedure where kidney from one person (donor) is removed and placed in the body of another person (recipient) in order to replace the deficient or inefficient kidney. The major problem that can occur with kidney transplantation is graft rejection. This rejection can cause severe consequences in the recipient. This happens due to activation of the immune system in the recipient. Since the function of immune system is to destroy any outside invaders like bacteria, virus and parasites, it may be activated against the donor kidney considering it to be foreign body. This activation of immune system against donor kidney can either be cell –mediated (due to cells such as macrophages and lymphocytes) or by components such as antibodies or the complement system. This activation leads to graft rejection. Rejection of graft mediated by antibodies is called AMR (antibody-mediated rejection). It is also referred to as B cell mediated or humoral rejection.

The types of AMR are as follows:

• Hyper acute rejection-this rejection happens within minutes of completion of surgery. This type of rejection may even cause death. It occurs because of presence of preformed antibodies present in high amount
• Acute rejection-it may happen from first week after surgery to three months after. It occurs because of development of antibodies after transplant surgery. It is less severe than hyper acute rejection
• Chronic rejection-it happens over a long span of time of many years. This causes damage to the transplanted organ over prolonged period.

AMR is an important factor which prevents prolonged survival of donated kidney in certain patients. The diagnosis of AMR can be made by presence of specific antibodies, specific histopathological changes and C4D (C4 complement component) deposition in peritubular capillaries of donor kidney.

Why is Immunohistochemistry (IHC)-C4D test prescribed?

The health care provider may prescribe IHC-C4D test in a patient with kidney transplantation to diagnose acute AMR (antibody mediated rejection). It helps to assess the prognosis (AMR is associated with poor prognosis). It also aids in deciding an optimal treatment plan in these cases.

Procedure and prerequisites

For the detection of AMR, transplanted renal tissue biopsy is sent to the laboratory. Renal biopsy specimen taken for histopathological examination should be handled with utmost care and precautions. The specimen is immersed in formalin. Container should be labelled properly with necessary details. Relevant clinical history/physical examination findings/radiological reports must be sent along with the sample. A properly filled requisition form must accompany the sample.