From the Nate Hellman Unpublished Archives: Proteinuria Values

When it comes to monitoring proteinuria, some nephrologists prefer following urine albumin levels, whereas others prefer monitoring urine protein levels. While there is nothing inherently wrong with either, it is helpful to keep the following reference values in mind, particularly when a single patient has both proteinuria and albuminuria values in his/her medical record.

First, however, one must consider the definition of "proteinuria." Everybody has some degree of proteins in their urine: what defines an "abnormal" degree of proteinuria has been the result of countless epidemiological studies and is still being refined today. It has been argued that our threshold of what constitutes "abnormal" should probably be lowered. In a normal individual, the standard breakdown of normal urine protein is about

• 40% albumin
• 40% Tamm-Horsfall protein produced by tubular cells
• 20% low molecular weight immunoglobulins.

Dipstick analysis is usually the first (and cheapest) test which reveals the existence of proteinuria. In the absence of protein, the dipstick panel is yellow; proteins in solution interfere with the tetrabromophenol indicator, resulting in the panel turning various shades of green.  Of note, this technique does not detect urine immunoglobulins, so this may miss patients with paraproteinemias.

The limit of detection of the urine dipstick (converting to the familiar "mg/day") for urine protein is about 150mg/day, or about 300mg/day of urine albumin.  

However, it's well-known that microalbuminuria--the existence of abnormally high amounts of albumin in the urine despite having a negative urine dipstick.

From the Nate Hellman Unpublished Archive: Xanthogranulomatous Pyelonephritis

Image from Radiology Picture of the Day
http://www.radpod.org/2007/06/19/xanthogranulomatous-pyelonephritis/

Xanthogranulomatous pyelonephritis (XGP) is a rare but severe complication of chronic UTIs. I think of it (in simplistic terms) as a pyelonephritis so severe that it results in loss of renal function of the affected kidney as well as being a severe intra-abdominal abscess which can spread to other tissues. In fact, the disease is sometimes referred to as a "pseudotumor" in that it has the ability to "metastasize" to other tissues and often has the radiographic appearance of a renal cell carcinoma on imaging studies. Treatment involves iv antibiotics and very often requires urgent nephrectomy, meaning that a Urology consult should be on-board as early on as possible. Most cases of XGP are unilateral and thought to be secondary to chronic urinary tract infection, often associated with staghorn calculi and chronic obstruction. The most common organisms causing XGP are E. coli, Proteus, and Pseudomonas. Histologically, XGP demonstrates lipid-laden foamy macrophages on a background of diffuse renal parenchymal necrosis.

From the Nate Hellman Unpublished Archive: microRNAs and the Kidney

MicroRNAs: one of the sexiest topics in the science community these days! Pick up a copy of Science, Nature, or Cell and you can usually find something to do with microRNAs within. What do these have to do with the kidney? Well, it's still a little premature, but there are certainly microRNAs present in the kidney, and recent studies have demonstrated that specific microRNAs are upregulated in conditions such as polycystic kidney disease and renal cell carcinomas, for instance.

How microRNAs work: microRNAs are single-stranded RNA molecules of between 21-23 nucleotides in length which are partially complementary to regions in multiple mRNAs. Once they bind to these mRNAs, the microRNAs either inhibit translation or completely degrade their target RNAs. A specific enzymatic machinery--comprised of the proteins Dicer and the RISC complex--is responsible for inhibiting mRNAs via microRNAs.

In essence, the power of microRNAs are that a single microRNA can regulate the expression of multiple genes working in parallel to achieve a similar biologic effect. This technology is of particular use to the pharmaceutical industry: one can envision targeting a particular microRNA which inhibit several pathways to prevent a disease process, such as atherosclerosis, renal fibrosis, or cyst formation to think of a few possibilities. The field is still very new. I wouldn't be surprised if a future Nobel Prize came out of this work. Three scientists (Drs. Ruvkun, Baulcombe, and Ambros) working on microRNAs recently won the 2008 Lasker Prize--considered by many to be the "precursor" prize to the Nobel.

From the RFN archives: The Brenner Hypothesis

The Brenner Hypothesis--developed by Barry Brenner of the Brigham and Women's Hospital, author of the well-known Brenner & Rector "The Kidney" textbook--states that individuals with a congenital reduction in nephron number have a much greater likelihood of developing adult hypertension and subsequent renal failure. This hypothesis is supported by the observation that there is a strong epidemiologic relationship between intrauterine growth retardation (IUGR)/low birth weight and adult hypertension. The mechanistic explanation for this phenomenon is that compensatory hyperfiltration by the remaining nephrons--similar to what happens in diabetic nephropathy--results in accelerated renal decline. While this theory is appealing at several levels, it does not explain everything: for instance, why most kidney transplant donors, who instantaneously lose 50% of their nephron mass, for the most part do well post-transplant without developing hypertension or renal disease.

The Brenner Hypothesis is part of a larger body of work which posits that many common adult diseases (including diabetes and hypertension) are caused by factors which are established during early growth and development, the "fetal origins of adult disease" hypothesis.

Originally posted by Nate Hellman

Nathan Hellman Memorial Award

Nate Hellman MD PhD, the founder of the Renal Fellow Network, died tragically just over two months ago. He was a wonderful person, who possessed a strong sense of humanity, humor and compassion. Nate touched the lives of many people and is dearly missed by all who knew him.

A graduate of the Medical Scientist Training Program at Washington University, Nate loved the mysteries of basic science and clinical medicine and who took immense pleasure in teaching and sharing knowledge. Presently, his family is working with Washington University to establish the Nathan Hellman, M.D., Ph.D. Memorial Award, which will be given annually to recognize an outstanding medical student in the School of Medicine, a fitting legacy for an incredibly accomplished physician and scientist such as Nate.

If you would like to donate to this endowment student award, details may be found here.

Nathan Hellman Rest In Peace

It is with great sadness and sorrow that I am writing to inform you of the passing of Nathan Hellman, MD, PhD, and founder of the Renal Fellow Network Blog. I worked with Nathan in the Division of Nephrology of the Department of Medicine, Massachusetts General Hospital (MGH), Boston, where we were both fellows. He passed away on February 13, 2010 at the Massachusetts General Hospital after a short illness.

Born in Houston, Texas, on December 8, 1973, Nathan grew up in Duluth, Minnesota. He attended Yale University, graduating magna cum laude. After Yale, he went to Washington University, where he obtained his MD/PhD. He did his residency training in Internal Medicine at University of Pennsylvania and became a member of the Division of Nephrology in 2007 as a clinical fellow in Nephrology. He was completing his fellowship as a research fellow and member of Iain Drummond’s research group. He was to be appointed a faculty member in July 2010.

Nathan was most importantly a wonderful husband, father, son and brother. At work, he touched all of our lives with his warm heart and spirit, great sense of humor and remarkable intellect. He was an exceptional scientist, a talented and insightful clinician and a remarkably kind and humble human being. He is survived by his wife, Claire, his two children, Sophie and Max, his parents, Dr. and Mrs. Hellman, his two sisters, and their families.

A Memorial Service will be held to celebrate his achievements and commemorate his contributions to the MGH community at the O’Keefe Auditorium on Wednesday, February 17th at 2pm, followed by a reception in the Thier Conference Room at 3.30pm.

In lieu of flowers, memorials can be sent to:

Nathan Hellman Memorial Fund
PO Box 471044
Brookline Village, MA 02447

Did you know your endothelium is hairy?

Just heard an interesting talk on endothelial dysfunction and its relation to nephrology.  One thing I learned is that the vascular endothelium is actually "hairy", as demonstrated from this electron micrograph (taken from this website). These little hairs are the endothelial glycocalyx, a gel-like layer of negatively charged proteoglycans and membrane glycoproteins which helps serve as a protective barrier from blood flow for the endothelial cells. You can't see it on standard light microscopy since it apparently requires special preservation techniques not normally used.  There is some data to suggest that vasculopaths and diabetics have a less developed and overall thinner endothelial glycocalyx compared to healthy controls, suggesting the importance of this structure in maintaining a healthy vasculature. 

In the kidney, the glomerular endothelium is a little different than most other endothelia in that they contain fenestrae:  actual pores in the endothelial cells which are large enough to let most proteins pass through, but small enough to exclude circulating blood cells. The glomerular fenestrated endothelium makes up a component of the glomerular filtration barrier (along with the glomerular basement membrane and the podocyte layers), and the classic teaching is that the negatively charged proteoglycans on this layer help form part of the charge barrier keeping albumin from getting filtered (though this is now being debated by some). Here are some pretty pictures of the glomerular fenestrated endothelium:

World Series of Poker Celebrity Kidney Transplant Recipient

Meet Jennifer Harman. She is apparently one of the most famous female professional poker players in the world, having done quite well at the prestigious "World Series of Poker" tournament. It turns out she is also a kidney transplant recipient, having undergone 2 transplants. Admirably, she has become a real advocate for patients with kidney disease, seeking to raise awareness for living organ donation. Recently, she announced that she would be donating 1% of all profits to the NephCure foundation, which funds research relevant to nephrotic syndrome and FSGS in particular.

Super Bowl Sunday Contrast Nephropathy Post

How common is contrast nephropathy in the general outpatient setting? When you send one of your outpatients to get a CT scan with iv contrast, what is the real risk?  Much of the randomized, controlled trial data on contrast nephropathy comes from INPATIENTS undergoing angiography or other procedures, often focusing on those with the greatest perceived risk of contrast nephropathy (e.g., diabetics, those with underlying CKD to begin with) in order to generate enough meaningful datapoints for analysis. An article by Mitchell et al in this month's CJASN reports the risk of contrast nephropathy in a mixed OUTPATIENT group--and finds that the risk of contrast nephropathy may actually be higher than what has generally been appreciated.

One big caveat, in my mind: even though the article is entitled, "Incidence of contrast-induced nephropathy after contrast-enhanced computed tomography in the outpatient setting," the phrase "outpatient setting" should be examined a little more closely. Their patient population wasn't exactly "outpatient" as we normally think of it; it was all the patients entering a large, academic emergency department who underwent CT scans with iv contrast. One could argue that by the very nature of their showing up in an emergency department (as opposed to their primary care physician office) they could be seen as "sicker" and therefore more susceptible to the effects of iv contrast use. Nonetheless, the researchers found that the incidence of contrast nephropathy (defined as an increase in serum creatinine greater than 0.5 mg/dL or greater than 25% of baseline between 2-7 days after contrast administration) was 11% (70 out of 633 patients receiving iv contrast), which is quite high. Not surprisingly, the development of CIN was also associated with an increased risk for developing severe renal failure and death.

There's still a lot of controversy about contrast nephropathy and just how significant it is--after all, the vast majority of patients see a return of their creatinine to baseline levels--but perhaps the knowledge that over 10% of patients in an emergency department show evidence of renal injury with a simple CT scan with iv contrast should make us think twice about ordering this test so frequently. 

Making Allograft Nephrectomies More Routine?

As much as kidney transplant outcomes have improved over the decades, we're not perfect: a sizable group of patients end up transitioning to dialysis therapies after the kidney transplant stops working. What should be done with the allograft once you've given up hope for any meaningful allograft function? In many transplant centers, the prevailing wisdom is simply to leave the allograft in place, as long as it is not causing any exceptional systemic inflammatory response as a result of prolonged rejection. If nothing else, it avoids an additional surgery in a dialysis population that is often plagued with comorbidities and the potential for surgical complications.

However, a recent study in this month's JASN by Ayus et al suggests otherwise, hinting that allograft nephrectomy might be considered as a more routine measure. The investigators probed the USRDS, looking at all transplant recipients who returned to long-term dialysis. A retrospective analysis demonstrated that those patients who had undergone an allograft nephrectomy had a 32% lower adjusted relative risk for all-cause death, even after controlling for factors such as age, comorbidities, and donor characteristics. The authors end the article by suggesting that "routine allograft nephrectomy in stable dialysis patients with a failed renal allograft should be evaluated against current management strategies in a randomized trial."

An accompanying editorial cautions against adopting this strategy too readily. They point out that patients in the allograft nephrectomy group tended to be younger and healthier, and even with appropriate adjustments to account for this, residual confounding and selection bias may well be altering the results. They also point to evidence that keeping the allograft in may actually be beneficial from an immune standpoint. Still, however, the retrospective by Ayus et al is intriguing and will doubtlessly be pursued further.

Drug Trials

Last week's poll results:  who should provide funding for large, randomized controlled drug trials?  Most respondents (58%) chose the diplomatic answer and said that it should be a combination between government and pharmaceutical companies.  I was somewhat surprised to note that more people felt that conducting RCTs should be the responsibility of the government (24%) rather than a responsibility of the pharmaceutical industry (only 7%), one of the most profitable industries within the U.S. currently. 

Check out the new poll question of the week in the right margin.

The actin cytoskeleton of the podocyte

Peter Mundel, a well-known researcher of podocyte biology, gave our Renal Grand Rounds today.  Here's what I took away from this morning's talk:

-regulation of the podocyte's actin cytoskeleton is postulated to be the final common pathway in most instances of nephrotic syndrome/proteinuria.

-in some ways it is better to think of the podocyte as a modified smooth muscle cell rather than a modified epithelial cell based on its intricate network of actin & myosin which mediate contractility.

-the medication cyclosporine (used in the treatment of some refractory forms of nephrotic syndrome) acts NOT on modulation of immune cell function as previously assumed, but rather on direct effects on the podocyte actin cytoskeleton, as detailed in a prior post.

-a key event in generating abnormal, protein-leaking podocytes is turning them from a stationary cell to a motile one.  This key transition is mediated by three distinct Rho GTPase proteins, already established to mediate motility in several cell types. In general, Cdc42 and Rac1 promote podocyte motility, whereas RhoA promotes podocyte stabilization. It is possible that targeting these Rho GTPase pathways could lead to novel therapies for podocytopathies, and this is being investigated.  

Check out a good 2009 Kidney International review of the topic by Mundel and Reiser.

How Luminex Beads Work

You may have come across the phrase "Luminex beads" while doing your transplant nephrology rotation, or heard the term while hanging out in the Tissue Typing Lab. This post is intended to briefly describe the Luminex technology and how it works. A good review by Tait et al can be found here.  

Acute cellular rejection in kidney transplant recipients comes from the presence of recipient anti-HLA antibodies directed against donor antigens. How do we detect such antibodies and prevent donor-recipient mismatches from occurring? Traditionally--and still one of the most practical tests--we use the complement-dependent cytotoxicity (CDC) "cross-match" assay. While useful, however, more recent "solid-phase" technologies have allowed a more sensitive detection of anti-HLA antibodies in recipient serum, and the Luminex system is one of them.  

Briefly, the Luminex technology consists of a series of differently-colored polysterene beads, populations of which contain distinct HLA molecules attached to them. The lab incubates an aliquot of the kidney transplant recipient's serum with an aliquot of beads, and if there are any anti-HLA antibodies present they will bind to the beads. A second phycoerythrin-labelled anti-human IgG antibody (aka, a "secondary antibody") is then added, and after washing off unbound antibody, the beads are passed through a machine which works like a flow cytometer, dropping beads one-by-one through a narrow chamber. As the beads pass through the chamber, they are hit with lasers of a specific wavelength, exciting both the fluorescently-labeled secondary antibody AND the fluorochrome within the bead itself--thus allowing the detection and identification of specific recipient antibodies.  

There are different types of beads:  for example, some beads are coated with many different Class I or Class II molecules, designed to detect a wide range of recipient antibodies. Some beads are designed to be like a single cell, containing HLA antigens encoded by two different alleles from each of the Class I (HLA-A, B, & C) and Class II (HLA-DP, DQ, DR) loci. Finally, there are the "single antigen beads" (SAG), a bead coated with one sole antigen. This can be particularly useful in patients with a high PRA (panel reactive antibody)--you can actually identify the specific HLA antigens to which the individual is sensitized.  

While potentially quite useful, it is important to also realize the limitations of this technology. While much more sensitive than the standard CDC cross-match, it is not always clear what a positive antibody result means--though in most instances, the CDC cross-match is still the primary determinant as to whether a given kidney donor-recipient pairing is deemed acceptable.  

Green Peritoneal Dialysis Fluid

This month's Kidney International "Nephrology Image" features a report by Chen et al in which they describe a PD patient who noted cloudy, deep green dialysate fluid upon drainage of their peritoneum. They also presented with right upper quadrant pain and fever. Peritoneal white cell count was elevated with 84% neutrophils. The diagnosis? Gallstone peritonitis. The patient had a distended gall bladder with multiple pigmented stones; the greenish color is presumably from extravasated bile fluid. The authors make the case that "appearance of green color in the peritoneal dialysate should lead to immediate investigation of the biliary tract in patients with our without abdominal symptoms [as] asymptomatic perforation of the gall bladder has previously been reported."

AJKD Bundling Editorials

This month's issue of AJKD includes an enlightening group of 6 editorials, each written from a unique perspective (e.g., the perspective of large dialysis corporations, the perspective of the ESRD Networks, the perspective of non-profit dialysis corporations, etc.), commenting on the proposed prospective payment system (PPS) for ESRD. The PPS is the so-called "bundling plan" which will radically change the way in which dialysis is reimbursed. For historical reasons, dialysis treatments are reimbursed based on 2 payments: (1) a flat-rate fee for the dialysis procedure itself (which dialysis units make very little, if any, profit on), and (2) "separately billable items", including injectable drugs such as Epogen, which in recent years have provided the majority of profit for dialysis units.

This will all likely change in the coming months as the PPS nears finalization. A single lump-sum payment will be charged which will taken into account not only the dialysis procedure but also all medications and laboratories provided during the dialysis procedure. Proponents of the PPS would argue that the ESRD Program already soaks up a large chunk of the Medicare budget (5.8% of the overall budget, despite affecting less than 1% of Medicare beneficiaries), and the "bundling" strategy will encourage nephrologists to use tests and medications (particuarly EPO) more judiciously, resulting in lesser overall costs.

However, there are several controversies with the PPS alluded to in many of these editorials. For instance: in the new plan, all labs ordered during dialysis would be included in the bunding plan. For instance, patients who need to have their INR monitored frequently can have their bloods drawn during dialysis, a practice which is probably both humane and having practical sense from a standpoint of preserving the vasculature for future fistula use. However, many are concerned that dialysis units will be resistant to provide this service for patients, as they will no longer be reimbursed for drawing these labs. Some point out that decreased lab work provided during dialysis will also have a negative effect on completing kidney transplant evaluations in a timely manner. Still others are concerned that many ESRD-specific oral medications (e.g., phosphate binders, cinacalcet) will also fall into the bundled payment: for nephrologists who are responsible not only for the health of their patients but also the health of their dialysis unit, might this not put nephrologists in the unenviable position of having to "ration" expensive oral drugs only to the patients deemed to deserve them the most? Finally, there is also concern that only the largest dialysis corporations will be able to compete with the new regulations, leading to the closure of several smaller and non-profit dialysis centers.

The final PPS is apparently still being tinkered with, so we don't know the exact details quite yet. However in reading these editorials it is clear that there remains some trepidation about how the bundling will change the dialysis landscape.

A Divided Consensus on Health Care Reform

Interestingly, there was a near 50-50 divide on last week's poll question regarding the surprising election of Republican Scott Brown to the U.S. Senate in the state of Massachusetts.  Many viewed the election as a referendum on public support of the health care reform movement, and if we are to believe this to be true then there are some significant public misgivings about the health care plan in its current form.  Amongst readers of Renal Fellow Network who responded to this poll, there were 45 votes who felt that Brown's election was a good thing and 43 votes who felt it was not--a roughly even divide.  Does that mean there is a roughly 50-50 divide of Republicans & Democrats amongst Nephrologists?  I'm not sure, but if so it would seem to parallel the current partisan divide within our country.

Check out the new poll question in the right margin which deals with funding of large randomized controlled trials of important drugs.

Potential Use of Rituxan in Membranous Nephropathy

Take-home points from Mayo Clinic's Fernando Fervenza's excellent Renal Grand Rounds this morning, in which he addresses the potential use of rituximab as a treatment for membranous nephropathy:

-the "rule of thirds" that we learn about membranous nephropathy (e.g., 1/3 of patients will spontaneously remit, 1/3 of patients will stay the same, and 1/3 of patients will progress to ESRD) is not entirely accurate in that patients with an extremely high degree of proteinuria (e.g., more than 8-10 grams per day) have a very high rate of progression of kidney disease.  This becomes critical in interpreting the results of clinical trials; you really have to look at the baseline proteinuria characteristics of the cohort.

-in non-randomized controlled trials, investigators are finding that dosing Rituxan either using a 1gm iv at D+1 and D+15 protocol OR using a 375 mg/m2 every 4 weeks for 4 doses total leads to at least a partial remission in between 60-75% of membranous nephropathy patients, a rate which is seemingly greater than one would expect for spontaneous remissions. One such paper by Fervenza et al is shown here.  

-a randomized, controlled trial comparing Rituxan to another therapy (e.g., Cytoxan-prednisone or a calcineurin inhibitor) would really be necessary to fully recommend using this strategy in the treatment of membranous nephropathy.  However, it is not clear where the money for performing such a trial would or should come from--industry or government.  

-it may be necessary to look at longer end-points to fully assess the effectiveness of Rituxan.  Since Rituxan targets pre-B cells but not plasma cells, you presumably have to wait until the plasma cells die off for it to have full effect.  Furthermore, monitoring proteinuria (the current standard for evaluating clinical response) is not perfect since it may reflect chronic podocyte damage (which may take months to years to fully heal, if it ever does) rather than immunologically-mediated proteinuria.  

-it looks as if levels of the antibodies against the phospholipase A2 receptor which explains a good chunk of patients with membranous nephropathy correlates generally well with patients who respond to Rituxan; that is, patients who successfully achieve a remission with Rituxan tend to show a complete disappearance of this antibody as assessed by Western blog.  Although this does not prove causality, it does point to a potential means of monitoring patients for a potential response.  

The Business of Dialysis

An interesting figure in this month's ASN Kidney News details the quarterly earnings for three major dialysis companies in the U.S.: DaVita, Dialysis Corporation of America (DCA), and Fresenius.

Also included in the figure (not shown here) is the "revenue per treatment"--that is, how much profit each company obtains from the average patient's dialysis run. For example, Fresenius reported a revenue per treatment of $348 for the 3rd quarter of 2009. I'm not sure how they arrive at these numbers, but you can do a quick calculation to figure out how much a single patient dialyzing on the standard 3x/week schedule is worth to the company on a yearly basis: $348/treatment x 3 treatments/week x 52 weeks/year = $54,288.00/year. Like it or not, dialysis is also a business.

ASN's New Logo

The American Society revealed its new logo with the new year: a male form with two glowing kidneys visible inside him, striding into the future (at least, that's my interpretation as to what he is doing--I guess alternate interpretations could include his being in the process of falling down, or perhaps hailing a cab...)

The logo replaces the traditional ASN logo, which is fairly simple:

You can learn more about the new ASN logo on the ASN homepage (just click on Mr. Kidney), but briefly the new logo is intended to go along with the ASN's new tagline, "Leading the Fight Against Kidney Disease," and is supposed to place greater emphasis on ASN's leading role in patient care and important kidney-relevant policies.

Interferon effects on the kidney

Interferons are cytokines which play a central role in the inflammatory response, and commercially prepared interferons have proven useful in the treatment of several diseases. For instance, interferon-alpha (often used in conjunction with ribavirin) is often used in the treatment of hepatitis C, and has also proven useful in the treatment of certain cancers, such as malignant melanoma. Interferon-beta has also been very successfully used in the treatment of multiple sclerosis. With the increasing use of interferons, however, has come the realization that they can have renal side effects in some patients.

A variety of mechanisms of injury have been reported, though most attention has focused on the ability of interferon therapy to cause proteinuria and nephrotic syndrome. This has been noted most commonly with interferon-alpha therapy, though in many of the patients with hepatitis B or C it may be difficult to be certain whether or not the development of nephrotic syndrome comes from the interferon therapy or a direct hepatitis-mediated renal injury such as MPGN. There have also been some recent case reports suggesting that interferon-beta can also cause a minimal change nephrotic syndrome in patients treated for multiple sclerosis and malignant melanoma.

Other mechanisms of renal injury reported with interferon use include acute tubular necrosis, acute interstitial nephritis, and even hemolytic-uremic syndrome. Occasionally, tubuloreticular structures as seen on electron microscopy of a kidney biopsy can be a clue as to the diagnosis of interferon-induced renal injury; these may also be seen in HIV-associated nephropathy.