Why All That Blood Work Before a Kidney Transplant Actually Matters

Over 90,000 people are waiting for a kidney transplant in the United States. People who need a transplant start with an evaluation. The evaluation includes multiple blood tests. These are crucial for the health of the recipient and the kidney after transplant.

Blood tests are needed to match recipients with donated kidneys. The recipient is the person receiving the kidney. The kidney comes from a living or deceased donor. The United Network for Organ Sharing (UNOS) is a non-profit organization that matches organs with individuals in need of a transplant. Below is a breakdown of the importance of transplant-specific labs.

Blood Type

You might already know your blood type. However, people needing a transplant must complete a blood type test twice. UNOS requires this for safety reasons. Recipients and donors with compatible blood types have a lower risk of complications. In a kidney transplant, it does not matter whether the blood type is “positive” or “negative."  

HLA and PRA

In addition to blood type, human leukocyte antigens (HLA) are used to match recipients with donated kidneys. HLA are proteins on cells. HLA can be thought of as “flags” for the immune system. These “flags” show whether the cells belong to the body. The goal of the immune system is to destroy cells with unfamiliar "flags", which do not belong in the body. The immune system is less likely to attack an organ that has similar HLA.

The panel reactive antibody (PRA) shows how sensitive a recipient is to other HLA. PRA levels can be high if the body has formed antibodies to other HLA in the past. Events that can cause a rise in PRA include:

·       Blood transfusion

·       Pregnancy

·       Previous organ transplant

People with a high PRA have fewer organ matches. However, UNOS utilizes a complex algorithm to ensure that everyone on the waitlist receives equal opportunities for kidney offers. People with a very high PRA might be recommended for treatment that lowers their PRA. The transplant doctor discusses this option with the recipient if it is recommended.

Infections

Detecting infections before transplant is crucial. After transplant, recipients start taking medications that weaken their immune system. In a weakened state, the immune system is less likely to attack or “reject” new kidneys. These medications, often called "anti-rejection medications", reduce the risk of rejection and increase the success rate of the new organ.

However, a weakened immune system means a weakened defense against disease. This is why infections must be treated before transplant surgery. UNOS requires recipients to be tested for infectious diseases such as HIV, hepatitis, and more. People with active HIV must be treated and cleared by a specialist before transplant. People who do NOT have antibodies (protection) against hepatitis will need to be vaccinated.

The purpose of testing for infections is to prevent any complications after transplant surgery. Fighting off infection requires a strong immune system. Strengthening the immune system after transplant involves reducing the amount of anti-rejection medications. This can result in rejection of the new organ.

Additional Blood Tests

Kidney transplant evaluations require a considerable amount of blood work. Some tests are only needed once. UNOS requires some tests to be repeated every year. Additional blood tests might be needed based on a person’s medical history. The purpose of this lab work is to provide the best outcome for a recipient and their kidney after transplant.

Sources

90,000 People Are Waiting for a Kidney. Here's One Way to Get Them a Kidney Faster. (2025, January 2027). Retrieved June 18, 2025, from  https://unos.org/news/90000-people-are-waiting-for-a-kidney-heres-one-way-to-get-them-a-kidney-faster/#:~:text=At%20any%20given%20time%2C%20nearly,transplants%20possible%20for%20Medicare%20patients.

Bhaskaran, M. C., Heidt, S., & Muthukumar, T. (2022). Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney International Reports, Vol. 7 (6), 1179-1188. https://doi.org/10.1016/j.ekir.2022.03.006.

Center for Disease Control and Prevention. (2024, March 8). Clinical Guidance for Transplant Safety. https://www.cdc.gov/transplant-safety/hcp/clinical-guidance/index.html#:~:text=Laboratory%20Testing%20for%20Infectious%20Diseases,Toxoplasmosis%20(for%20deceased%20donors%20only)

Delves, P. J. (n.d.). Human Leukocyte Antigen (HLA) System. Merck Manual Professional Version. https://www.merckmanuals.com/professional/immunology-allergic-disorders/biology-of-the-immune-system/human-leukocyte-antigen-hla-system

National Kidney Foundation. (n.d.) Blood Tests for Transplant. https://www.kidney.org/kidney-topics/blood-tests-transplant

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