Race Correction in Kidney Function Algorithms and Disparities in Kidney Transplant Wait List Time

Bias in Healthcare Algorithms

It is National Kidney Month! \ During graduate school, I worked in Transplant Medicine at Medstar Georgetown Transplant Institute. Since I was studying epidemiology and data science, I searched for ways to combine my interests. Eventually, I stumbled into learning about Bias in Healthcare Algorithms. I plan to explore algorithmic bias in public health more in the newsletter. Stay tuned!

Eliminating the CKD-EPI equations race coefficient from kidney transplant eligibility criteria could reduce transplant wait times for African Americans thus reducing the disparity in time to transplant. Overall, African Americans who have higher rates of diabetes and hypertension are more likely to not get listed for a transplant compared to other groups and have longer wait times. (Schold et al.) Some argue that the race correction in the CKD-EPI equations estimation of glomerular filtration rate(eGFR) plays a role in this. Researchers argue that removing race from the biased algorithm for GFR estimation could help reduce the time to transplant.

The eGFR is a surrogate marker for the number of functioning nephrons in a kidney. See the figure above to see a nephron. The nephrons are made of glomeruli and tubules. The glomerulus filters waste out of blood and the waste is carried away by the tubules. eGFR is used because getting a precise measure of glomerular filtration rate (GFR) involves using filtration markers such as inulin, iothalamate, or iohexol is more complicated and invasive.(Stevens et al.) There are three equations to estimate GFR the Cockcroft-Gault, MDRD equation, and the CKD-EPI equation. (Levey et al. “Gfr Estimation: From Physiology to Public Health”) The CKD-EPI equation is used the most often, so we will discuss this algorithm.

The normal GFR for a kidney is 120 to 130 ml/min/1.73m2.(Levey et al. “Gfr Estimation: From Physiology to Public Health”) At this GFR, the kidneys are functioning efficiently, and they are filtering out excess waste and fluid. In the hospital setting, GFR is used to understand patients’ symptoms, abnormal labs, adjust drug doses, and assess the risk of kidney disease. (Levey et al. “A More Accurate Method to Estimate Glomerular Filtration Rate from Serum Creatinine: A New Prediction Equation. Modification of Diet in Renal Disease Study Group”)

When an individual’s GFR starts to decline, they will likely progress through the five stages of kidney disease as seen above. The early stages of kidney disease may include a decline in GFR, but the patients are asymptomatic, from Stage 1 to Stage 2. Kidney disease is considered chronic when the GFR is below 60 ml/min/1.73m2 for three or more months. (Levey et al. “Gfr Estimation: From Physiology to Public Health”) This would be Stage 3a. As kidney function worsens, the patient will progress to Stages 3b and 4. When the kidney is no longer filtering waste out of the kidney, the patient will progress to end-stage renal disease, Stage 5. At stage 5, patients may be referred to dialysis or receive an organ transplant with a living or deceased donor. (Abecassis et al.) At stage 5, the patient will die without getting a kidney transplant. At each stage, GFR plays a role in assessing the patient’s risk of kidney failure.

When a transplant is considered an option for someone with Chronic Kidney Disease (CKD), they will go through some or all of the following steps. First, a patient’s nephrologist will determine if a patient is suitable to be referred to a transplant center. GFR is one of the considerations used. If they are suitable and want a transplant, they are referred to a transplant center. When a patient is evaluated for transplant, a medical review board at a transplant center decides whether the patient is suitable for transplant. (Arriola) The medical review board will review labs and major organ systems to see if they are any conditions that would make the transplant less likely to succeed. If they are found healthy enough for transplant and have financial and social support, the patient is added to the national transplant waitlist at United Network for Organ Sharing (UNOS). (Levin et al.) The CKD-EPI algorithm, which estimates GFR, is one of the components of this process. At this point, the patient could have a living donor or deceased donor transplant, which is partially determined by their GFR.

eGFR plays a role in the kidney allocation system. Under the current system of kidney allocation, kidney transplant candidates are not registered on the wait list until their globular filtration rate is decreased to 20 ml/min per 1.73 m2 or less per UNOS requirements. (Stevens et al.) For those who need a transplant, the waiting time is calculated using 3 criteria. 1. When the candidate starts dialysis 2. The eGFR is below 20 ML/min/1.73m2 and 3. the date the eGFR is less than 20 ml/min/1.73m2 and if they were registered before starting dialysis. (Procurement)

When looking at the supply of kidneys for this eligible for transplant, the demand for kidneys is far greater than the supply. In 2017, 30,918 candidates were added to the waiting list. (Hart et al.) However, only 20000 kidneys transplants were performed in 2017. Many patients wait for a kidney transplant and never receive one and eGFR plays a role in this. In 2007, 12 percent of waitlisted kidney transplant candidates were waiting 5 or more years versus 15 percent in 2017. There are trends that show that wait times are increasing for kidney transplants. (Hart et al.)