MADDIE SOFIA, HOST:
You're listening to SHORT WAVE from NPR.
Maddie Sofia here with Maria Godoy, science correspondent. Hi, Maria.
MARIA GODOY, BYLINE: Hi, Maddie.
SOFIA: So we've talked a good bit about racial health disparities on SHORT WAVE. And today you've got a story for us set in the world of kidney medicine. People in that field are questioning whether a diagnostic tool super widely used to assess a person's kidney health may actually disadvantage Black patients.
GODOY: Yeah. So this reexamination has been going on for years now, but it's really come to a head recently. It's being driven by medical students. And I want to introduce you to one of them. Her name is Naomi Nkinsi.
NAOMI NKINSI: I'm a third year MD-MPH student at the University of Washington School of Medicine.
GODOY: Now, back in her first year of med school, she remembers one day sitting in a lecture and the professor is talking about GFR or glomerular filtration rate.
SOFIA: Which is just how fast a person's kidneys filter blood.
GODOY: Right. And now, directly measuring it is pretty complicated. So doctors regularly do an estimate of people's GFR. It's also known as eGFR.
NKINSI: So generally speaking, higher eGFR equates to better kidney functioning, and lower eGFR equates to worse kidney functioning.
GODOY: So this professor brings up a slide and says basically, here's the equation for eGFR, and here's how the estimate of kidney function changes automatically if someone is Black.
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GODOY: This is why this measurement is controversial, because it treats Black patients differently from every other race. See, the calculation automatically adds a multiplier to Black patients' scores, and that increases their estimate.
SOFIA: Which has real consequences - right? - because among other things, those numbers are used to help determine who gets referred on a wait list for a kidney transplant. Right? Like, and there are also certain types of care that only happen at certain level of lower kidney function, that kind of stuff.
GODOY: Yeah, that's right. And in fact, there's a recent study that looked at what actually happened to kidney patients in the Boston area. And it showed that without this race coefficient, 64 patients would have hit the threshold for further evaluation.
So basically, the doctor would say, hey, let's look a little more closely into this, which could lead to a referral for kidney transplant. But in real life, with that race coefficient, that just didn't happen.
SOFIA: So they weren't basically sent for those further evaluations.
GODOY: Exactly. So back to Naomi, the med student. She's sitting in class learning about this race adjustment. And as a Black woman, she sees how it reinforces the idea that race is a biological construct instead of a social construct.
NKINSI: Oh, yeah. I made a huge stink (laughter).
GODOY: So Naomi puts her hand up.
NKINSI: I began posing a lot of questions, like, for example, can you explain to me the physiological reasoning behind melanin in my skin leading to different kidney functioning? What is the pathway for that, right? Like, how Black is Black enough to get this measurement?
What do you do with mixed-race people? If someone has a kidney transplant and they're white and they get a kidney from a Black transplant donor, is the kidney now Black?
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SOFIA: Just a guess here, Maria, but the professor didn't have any good answers to those questions.
GODOY: No. But Naomi and other students, they didn't stop raising them. They connected with other med students, with faculty members, the head of nephrology, aka the kidney division. And their advocacy, it worked. Last year, the University of Washington health system announced they would stop using this race-based eGFR equation in their labs.
SOFIA: Wow. I mean, that feels like that's got to be pretty big.
GODOY: Yeah. And other places have done this, too. But the race adjustment for eGFR is still being overwhelmingly used. And not everyone in kidney medicine is down with the idea of dropping race from the equation immediately. The debate about its value is ongoing.
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SOFIA: So today on the show, Maria leads us into that debate. We look at how the use of race in eGFR came to be and how it impacts Black patients today. This is SHORT WAVE, the daily science podcast from NPR.
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SOFIA: OK, Maria, in talking about this diagnostic tool for kidney health, I'm pretty interested in, like, how did race get incorporated into it in the first place?
GODOY: OK. So remember that measuring GFR is pretty cumbersome. So decades ago, researchers created a quicker, easier way to estimate it called eGFR. And to do that, they focus on, among other things, people's creatinine level, which they do because, as Naomi explains...
NKINSI: Creatinine is a byproduct of muscle breakdown that is filtered through the kidneys.
SOFIA: So doctors in labs measure how much of this waste product from your muscles is in your blood as a kind of proxy for how well your kidneys are doing their job.
GODOY: Exactly. And then race comes into play around 1999 because of a study. So researchers got a little over 1,600 participants, some black, some white. And it's unclear how researchers classified the participants' race because they didn't have specific criteria. So it was likely done just by looking at skin tone.
SOFIA: Wow. I don't even know where to begin with doctors guessing people's races, Maria. But on top of that, that sounds like a pretty small sample size for this sort of study.
GODOY: Well, and in fact, when you then break it up by the participants' race...
NKINSI: One hundred and ninety-seven were Black and one thousand three hundred and four were white.
SOFIA: Wow. OK, so their findings were based off of fewer than 200, maybe, Black people.
GODOY: Yeah. And the average Black person had higher creatinine levels than the white participants in the study, even if their actual GFR was the same when you measured it using the big, cumbersome process.
GODOY: So researchers introduced a race multiplier, adding a coefficient to the equation for Black participants. But critics like Naomi say, what this essentially does is normalize Black patients to white patients because white people are the standard.
NKINSI: That aside, you're making an assumption off of an entire population of people based on 197 participants.
SOFIA: And researchers attributed that difference in participants to just race. Like, did they look into any social determinants of health like diet or stuff like that?
GODOY: No. And they zeroed in on something problematic, race and muscle mass. Remember that creatinine is, among other things, a breakdown product of muscles. And the authors point to three prior studies suggesting Black people had more muscle mass than white people.
But those studies researchers cited were done between the 1970s and 1990. They were very small, and none of them even directly measured muscle mass.
VANESSA GRUBBS: The suggestion that Black people and only Black people are different than every other human on the planet is - to me, it's just ludicrous. And I just - it's really baffling how folks can keep hanging on to this notion because they believe it, not because they have any real proof of it.
GODOY: So Vanessa Grubbs is a kidney specialist at the University of California San Francisco and a longtime critic of using race-adjusted GFR. And she says, the idea that Black people have more muscle isn't rooted in good science, and it's just racist.
GRUBBS: I mean, it's completely ridiculous. I mean, what - all of this just flows straight out of trying to justify slavery, you know. And none of the studies that they cite in the original paper have much, if anything, to do with muscle mass. And it's certainly not something that you can generalize to all Black people.
SOFIA: Right, right.
GODOY: Right. And Vanessa and other critics say socioeconomic factors, not race, might explain the differences observed between Black and white patients in these studies. Diet and medications might also be a factor.
MALLIKA MENDU: If clinicians are going to use it, at a minimum, we need to be transparent with patients. So we have to be able to explain it to patients.
GODOY: Mallika Mendu is a kidney specialist who's looked into this. She's also the executive director of clinical operations for Brigham Health. She and Grubbs agree, if you can't explain precisely why these differences in creatinine exist, it's unscientific to be using these equations.
SOFIA: OK. So has there been research since this 1999 study or are we still basing this off of that one small, problematic study?
GODOY: Well, so there was a revision to the equation 10 years later after a larger study came out in 2009 and they had more Black participants. But what they found is similar to the 1999 study, that the race multiplier made the estimate more accurate.
GODOY: So they kept the multiplier for Black people that, yeah - it gives a higher estimated GFR than their white peers.
SOFIA: Meaning that Black patients' kidneys are estimated to function better.
GODOY: Right. Higher number equals higher kidney functioning, broadly speaking. But people like Mallika Mendu, they point out that, really, for a lot of patients across races, not just Black patients, there was a sizable difference between their measured and estimated GFRs, suggesting that eGFR is imprecise.
SOFIA: Oh, OK. So, like, this estimate isn't super precise, really, for anyone.
GODOY: Yeah. And that's just one of the reasons Mallika wants to get rid of it. She points out that race is a social construct, not a biological variable.
MENDU: And we know that there is more diversity within Black patients than there is genetic diversity between a Black person and a white person - right? Like, so to say that being Black is somehow a monolithic thing when it comes to genetics, when it comes to ancestry, I think is challenging.
GODOY: And here's the deal. Even people who want to keep the equation for now will agree with all that. But they also say...
NEIL POWE: Do we just ignore it? How do we treat data like that? It's real data, and it's how then do we use it (inaudible) thoughtful way?
GODOY: Neil Powe is a kidney specialist at UCSF. And he says, even if we don't have a concrete explanation for exactly why they exist, we can't just ignore these observed racial differences when they come up. If we do, he says, there is a chance, without knowing a person's true, measured GFR, that eliminating the race multiplier could lead to overdiagnosis of Black patients or make them ineligible for certain drugs.
Plus, Powe points out that getting rid of this tool won't just magically erase health disparities.
POWE: I think it's an over-exaggeration to say that the equations are, you know, causing the disparity. In fact, these disparities were in existence before the equation that included race came into being.
SOFIA: I mean, I kind of get that. But I feel like, you know, if the equation is making those disparities worse, you know...
GODOY: Well, he's also worried about what happens if there isn't a standard, like if some health systems drop this race adjustment and some keep it. Like, if you go to one doctor and get one number but you get a different number if you go to a different doctor, theoretically, your care could be different.
SOFIA: Like, because you'd end up on different parts of a threshold for a potential medication or something.
GODOY: Yeah, exactly.
SOFIA: Well, I mean, I don't - Naomi would argue that there isn't a standard now - right? Like, how do you, for example, how do you apply this to multiracial people? You know, that's one example.
GODOY: Yeah, that's a valid point. Even Neil Powe thinks so. But Neil says, there could be other potential, unintended consequences if you drop the race multiplier, for instance, kidney transplants. In general, it could result in fewer Black people being eligible to donate kidneys because when you remove that multiplier, kidney function seems lower.
And for those who do have kidney problems, it could affect which medications patients have access to, especially if they don't get their actual GFR measured. Plus, it could affect their life insurance possibly.
SOFIA: OK. OK. Are - I mean, Maria, are big organizations like the National Kidney Foundation taking notice and, like, doing anything about this, engaging in this debate?
GODOY: Oh, absolutely. They're actually part of a joint task force with the American Society of Nephrology.
SOFIA: Those are kidney specialists, right?
GODOY: Yeah, yeah, exactly. And actually, multiple people we heard from today are on that task force. They're working on issuing a new set of recommendations. But that'll take at least a few more months. But they are expected to put out some interim recommendations later this month. It's really unclear what the outcome will be.
I mean, everyone I interviewed for the story agreed that in an ideal world, we don't factor in race. No matter where they came down on dropping race-adjusted GFR, they all agreed with that. But what the best solution is, that's really just up for debate.
SOFIA: Yeah. I mean, you know, listening to this, I'm just thinking, you know, if we could more accurately measure GFR somehow, in an easy way, we wouldn't have to use this multiplier or, you know, if we found something else to estimate kidney function.
GODOY: Yeah. Multiple doctors I spoke to suggested alternatives, like an estimated GFR range or looking at other biomarkers, instead of, or in addition to, creatinine. But it could really land anywhere from eliminating the race-adjusted GFR altogether or maybe they tweak the equation or keep it with some asterisks.
Whatever the outcome, everyone agrees that eGFR should not be the sole tool doctors use to make decisions about patients' care.
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SOFIA: All right, Maria Godoy, we appreciate you. Thank you so much for bringing this important story.
GODOY: Yeah, of course - any opportunity to talk with you, Maddie.
SOFIA: (Laughter) miss you too, bud - miss you, too.
Today's episode was produced by Rebecca Ramirez, edited by Viet Le and fact-checked by Ariela Zebede. Neal Rauch and Josh Newell were our audio engineers. I'm Maddie Sofia.
Thanks for listening to SHORT WAVE from NPR.
GODOY: Bye-bye (laughter).
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