The Racist Past of Kidney Screening

This article was originally published in our Fall 2020 print issue.

UCSF made headlines in 2019 after a landmark decision to remove the factor of race from all of the kidney screening procedures at Zuckerberg San Francisco General Hospital. The decision was influenced by a recent spark in discussion of race in medicine following an article by New England Journal of Medicine analyzing the use of racial bias in various medical procedures, including kidney testing. 

The current procedure for kidney function testing measures the levels of creatinine in the patient’s blood, or waste products, and this value is used in a formula to find the patient’s estimated glomerular filtration rate (eGFR), which is how fast the kidneys filter blood. eGFR is then classified to be low, normal, abnormal, or abnormal critical. This classification is determined by comparing the value for eGFR to the set range of values for each level of function determined to the patient’s age, gender, body size, and race. It is understandable that an adolescent patient and a geriatric patient would have different levels of kidney function that would be considered healthy, or a man versus a woman. But why was this logic applied to race as well? 

Historically, eGFR was calculated using the Cockcroft-Gaft formula. This formula was developed in 1973 by using data of creatinine levels in 250 men, and utilizes age, gender, and body weight alongside creatinine values to calculate a eGFR. In the 1990s, however, it was noted that this formula underperformed in determining creatinine levels in black patients. This lack of accuracy was, at the time, attributed to the formula’s lack of distinction between lean body weight, or weight not including fat mass, and ideal body weight, which includes both. 

Thus, in 1999, the MDRD and CKI-EPI formulas were established and became the standard for measuring kidney function. These formulas corrected for Cockcroft-Gaft’s faults by taking the patient’s muscle mass into consideration. While surveying this consideration, the MDRD study surveyed that black patients had higher creatinine levels, thus race was added to further correct the formula for measuring eGFR, with the assumption that black patients had higher muscle mass due to their race . The kidney function score for black patients was multiplied by 1.212 before being compared to standardized measures of what is considered normal or abnormal. However, this correction for race based on muscle mass appears to be more based on the researcher’s ideologies of black patients than than true to reality. On the issue, Dr. Vanessea Grubbs, a nephrologist at San Francisco General Hospital, says in her article “Precision in GFR Reporting”, that this “effectively impl[ies] that blacks are biologically distinct from all other humans.”

To combat this, a study done at UC Davis in 2008 aimed to investigate this long held claim by attempting to find an association between body composition, or levels of muscle mass, and creatinine levels in over 3000 patients, about 50% of whom were black. Though the study did find that the creatinine levels in black patients were higher than non-black patients, there was no association found between these values and muscle mass of the patients. Looking back, MDRD formulas’ basis for giving black patients more normal eGFR rates was due to a flaw in the study’s design; the set of participants in the study had less than 200 black patients, and this underrepresentation is thought to have led to an inaccurate set of data. The legacy of this flawed data and formula has continued impacts on the lives of black kidney patients. 

Under the MDRD and CKI-EPI formulas, black patients and non black patients are measured based on two different standards. These standards determine what levels of creatinine are healthy for the individual, and use race to make the standard more precise. Dr. Grubbs explains that “no matter if one is 51%, 78%, or 22.56% of a race—a simple yes or no for “if black” appears to be all the precision we need.” For a non-black woman that is 55, a 2.8mg/ml level of creatinine qualifies them to need a kidney transplant. For a black woman of the same age with the same concentration of creatinine, they would not qualify for a transplant. 

This change in formula directly results in a change in quality of care, and subsequently quality of life for the patient. Not being qualified for a kidney transplant means a patient may have to live with a defunct kidney based on an arbitrary standard. This may leave many people falling through the gaps of patient care, which is a persistent problem in healthcare for black communities. 

This formula also badly accounts for other racial groups. Studies from India, Japan and Pakistan suggest that the measured average GFR for individuals in these regions is lower than estimated for these using the CKD-EPI equation for whites. The study behind the CKD-EPI formula also states that these differences were geographical and ethnic rather than based on race, thus using race as a heuristic is less than ideal.  

Though the specific solution to measuring kidney function accurately is not yet clear, it is clear that transitioning away from the CKD-EPI formula was a much needed change. It also has become clear that this is not the only area of medicine that is affected by prominent racial differences, as similar issues have been reported within cardiology and obstetrics. Medical racism is an issue at the forefront of public health, and we must continue to analyze the mistakes in science of the past to create a healthier future for everyone. Dr. Grubbs says, “Let’s stop playing the race card like it’s a genetic marker. It simply is not.”