I have a patient who looks a lot like Denzel Washington to me. Book of Eli Denzel. Minus the dark glasses and shotgun. Even has similar mannerisms. The way he holds his mouth. His laugh. Now I’m not among the multitude of women who would consider wriggling out of her panties to throw them on any stage Denzel stood, so it’s not a problem for me. He just happens to be a good-looking brotha with a chronic kidney problem.
He had been a colleague’s patient for a year or so when front office staff mistakenly put him on my clinic schedule for his follow-up appointment. I apologized for the mix-up and with his permission went forward with the visit. I offered to make sure he was put back on my colleague’s schedule for follow-up. He said he would prefer to stick with me. He liked the way I explained things; he liked my get down.
That was nearly 5 years ago. Since that visit, he—and his lovely wife—have been coming to see me in clinic every 2 to 3 months or so.
Now like Denzel, my patient was quite muscular. But over the years as his chronic kidney disease has progressed, his muscles have wasted away a bit. When we met I needed a large cuff to take his blood pressure. Now a regular one will do.
Like most of my patients with chronic kidney disease, when he comes in for a clinic appointment, he wants to know how his kidney function lab test turned out very soon after "Hi how are you." I log into his electronic medical record and three clicks later I’m looking at his test results.
I scroll down the page to find creatinine and eGFR. Creatinine is a breakdown product of the muscles, produced at a fairly constant rate every day. We use the blood level of creatinine to estimate kidney function because it passes freely through the kidney’s filters but, for the most part, is not pushed out or pulled back into the body by the tubular cells that determine how much potassium and sodium and water et cetera is in one’s pee. The eGFR is the estimated glomerular filtration rate—about how fast the kidneys filter the blood. Getting closer to actual kidney function requires collecting one’s pee for 24 hours in addition to the blood test. Getting even closer to actual kidney function requires a research lab, an IV, repeated blood draws, and essentially all goddamn day—and even this is not the actual kidney function.
Fifteen years ago, a bunch of researchers published a study of about 1,600 adults in which they came up with the equations that we use to estimate kidney function. One just plugs in the patient’s creatinine, age, and gender and voila! —there you have an estimate of the percent kidney function the patient has. Quick and easy. Most labs do it for us now.
But wait—if the patient is black, you have to multiply by another number. Because blacks have higher muscle mass, the researchers determined. Another one of those byproducts of the slave trade, it’s presumed.
Of course one of the problems with generalizations is that they aren’t always true. And in Medicine in particular, they make us lazy and we often accept them without question—especially if they jive with our underlying assumptions, I believe.
I wonder how many health care providers looking at patients’ lab results make the mental adjustment that the “race adjustment” is really a proxy for muscle mass, rather than just focusing on the race of the person in front of them. And so if the person in front of them has a large, muscular frame, would they tell them the race-adjusted estimated kidney function even it that person wasn’t black?
I wonder how many realize the original study was based upon only about 200 black Americans to generalize to everyone. And that the study included no American Samoans, no Latinos, no Asians. These groups are simply “not black” in our equations. Just black people are different.
This shortcut can have a significant negative impact on black patients who happen to not have a high muscle mass— like my Denzel patient. A person can be placed on a kidney transplant waitlist when the eGFR is 20. The race-adjusted value is closer to 25. The difference between 25 and 20 can be several years for many patients. Years of accruing time on the kidney transplant waitlist. And those who have been on the waitlist the longest get kidneys first—sometimes without ever having to go on dialysis. And thirteen people on the waitlist die every day waiting for a kidney. This matters.
Some time ago, I explained this to my patient and asked him to collect a 24-hour urine sample so that we could get a more accurate measure of his kidney function. The 24-hour test result was the same as the “not black” eGFR. He’s been on the waitlist for a year now. His last race-adjusted eGFR was 24.