Proteinuria Plus eGFR Keeps the Nephrologist Away
Hi, I'm Dr. Henry Black. I'm Immediate Past President of the American Society of Hypertension and Clinical Professor of Internal Medicine at the New York University School of Medicine. I'm actually a lapsed nephrologist, having had my training in nephrology quite a while ago. I'm very interested right now in how we stratify patients in order to refer for care. There's a concern in the nephrology community that there simply won't be enough nephrologists soon, as the population ages and the incidence and prevalence of end-stage renal disease begin to increase.

The Kidney Disease Outcomes Quality Initiative (KDOQI) group put together a staging system for chronic renal disease several years ago -- about almost a decade ago -- from stage 0, which is no renal disease, to stage 5, which is end-stage renal disease. This was all based on estimated glomerular filtration rate (GFR). Stage 1 was 90 mL/min/1.73 m or more GFR, stage 2 was 60-89.9. Those were not considered to be significant end-stage renal disease and not necessarily something for which you referred a patient to a nephrologist. But if the estimated GFR was 45-59.9 (stage 3), then you did [refer the patient], or if it was stage 4, which was 15-29.9, you certainly did. Anything below that (stage 5) was end-stage renal disease and most of those patients will have a nephrologist, at least as part of the care team.

Now we've known from clinical trials and observational studies that the presence or absence of protein in the urine can have important prognostic significance. If you do a dipstick test and it's negative or trace, that's generally felt to be < 30 mg/g of creatinine. If you're 1+, that's between 30 mg to 299 mg, and if you're more than 300 mg of albumin per gram of creatinine, that's considered high or heavy proteinuria. How does that impact the staging system? If it turns out that the presence of protein is just as important as the level of GFR, or if it affects whether you would refer a patient, it'd be interesting to see if that would work.

Well, a group in Alberta looked at the population in that area -- almost 900,000 people. They took about 450,000 of them to try this system and another 450,000 to validate it. What they found is that if you added whether there was light or no proteinuria, moderate proteinuria, or heavy proteinuria to the estimated GFR from the staging system, then they could get a much better prediction of people who wouldn't need referrals. But they didn't do as well when you look at people who developed chronic kidney disease later, which was the endpoint they were looking at.

So what this would mean is that there were more people who were upstaged to stage 0 or 1 (low-risk people) and fewer people in stage 3 or 4 than the old system, who would then need referral to a nephrologist. This can have enormous impacts on public health in that we don't need to spend resources and people don't really need that expertise. But there is a problem: what this system did is that it missed people who would have needed a nephrologist in the old system, but it also took away a lot of people who didn't need a nephrologist with the new system. So what are we doing here? Are we interested in the cases that have trouble or are we interested in preventing the use of money and resources for people who don't really need it? This is a common problem when we look at rare diseases, for example, as opposed to common ones, whether we're looking at relative risk or absolute risk, and all of the things that go into deciding where policy will be.

We can't possibly evaluate all the people who need it and we don't have enough nephrologists, I think that's pretty clear. And what to do, exactly, isn't clear as well. So I think this study adds a lot of interest, and I suspect that as the renal community gets together, they will adopt a staging system like this instead of simply using the 0-5 staging that we currently do. I look forward to seeing what they decide. Thank you very much.