Blood groups and transplantation

We all have a blood group from the ABO and rhesus systems. The ABO blood groups (A, B, AB and O) are important in transplantation as it is generally not possible to transplant an organ with an incompatible blood group.

Recipient	Donor blood group
	A	B	AB	O
A
B
AB
O

Blood groups and kidney matching

A patient with blood group AB can receive an organ from a donor of any blood group, whereas a patient with blood group O can only receive organs from blood group O donors. This would clearly be unfair, so the deceased donor matching schemes have rules to level the chances of transplant.

ABO-incompatible kidney transplants

Patients with a living donor can still be transplanted, even if the donor has an incompatible blood group, either by desensitisation treatment to remove the anti-A or anti-B antibodies or by through the National Kidney Sharing Scheme.

Desensitisation treatment

It is possible to do an incompatible transplant if there are only very low levels of anti-A or anti-B antibody. The levels can be measured and are called titres; 1:2 would be considered a very low titre and 1:256 would be a very high titre.

The titre is the most dilute concentration of recipient blood plasma that produces a detectable reaction when mixed with red blood cells of the incompatible blood type. 1:2 means that serum diluted 50:50 with saline produces a reaction, but diluting again to 1:4 shows no reaction. In contrast, 1:125 means that there is so much antibody present that the serum can be diluted 50:50 with saline 125 times and still produces a reaction.

We can generally do an ABO-incompatible transplant safely if the titres are 1:8 or lower, although 1:4 or lower is needed for incompatible transplants from some blood group A or AB donors.

The A and AB blood groups have various subtypes based on variations of the A antigen, of which the most common are A1 and A2. The A1 antigen is more likely to produce a reaction so incompatible transplants from A1 or A1B donors are only safe if the recipient anti-A1 titres are 1:4 or lower.

The desensitation protocol used in Glasgow gives an antibody called Rituximab 30 days before the planned transplant, which removes the white blood cells that make antibody. We then use a technique called plasmapheresis to replace plasma (which contains antibodies) with saline over a number of sessions of treatment a little like haemodialysis. The number of plasmapheresis treatments depends on the antibody titres before treatment and how quickly the titres are reduced by the treatment. Titres are checked again at the end of treatment and the transplant can only go ahead if the titres are low enough.

Around 1 in 4 of patients considered for ABO-incompatible transplant already have low enough titres before starting treatment and will not need plasmapheresis if the titres remain low.

The National Kidney Sharing Scheme (NKSS) is used to allow patients with a living donor unsuitable to donate to them directly to be matched to an alternative living donor who is suitable.

For example, Mr Smith needs a transplant, and his wife is happy to donate, but he is blood group A and she is blood group B. Mrs Jones also needs a transplant, and her husband is happy to donate, but she is blood group B and he is blood group A. The NKSS would allow Mrs Smith to donate a kidney to Mrs Jones while Mr Jones donates a kidney to Mr Smith.

The NKSS also allows transplants to go ahead for any other reason that makes a direct transplant difficult, including HLA antibodies or mismatch.