Everyone with PKD gets their GFR (Glomerular Filtration Rate, estimated or otherwise calculated) tested every so often, depending on the condition of the kidneys. Or at least, you should be. :) As I was curious, today I was researching just how they estimate your GFR and discovered that there’s some controversy from some doctors as to use and accuracy of some methods, and there are some caveats about its use.
Creatinine clearance (Ccr) measured from a 24-hour urine sample has traditionally been used to calculate your creatinine clearance, from which GFR could be estimated. That’s less popular these days because it can be incovenient, messy, and hard to get every last drop. So a lot of the time now your Ccr itself is estimated from your serum creatinine result, and then eGFR; or a formula is used which uses serum creatinine instead of an estimated Ccr.
Most pathology labs in North America, as I understand to be the case, use the Cockroft-Gault equation to estimate your creatinine clearance. This equation takes into account your age, sex and serum creatinine. In Australia and the UK, the MDRD (Modification of Diet in Renal Disease) equation is overwhelmingly used to estimate GFR, and takes into account your sex, age, and serum creatinine. There are a few other equations in use, but those are the most common.
However, like many pathology tests, they have their limitations. Here are some reasons why it could be a good idea to discuss your results more fully with your doctor:
- MDRD equation is based on a standardised body surface area of 1.73m squared. It’s thought to be accurate enough for people whose BSA is from 1.5-1.9m squared. It also takes into account whether you are African-American or not.
- If you are very underweight, very overweight, have muscle wasting from disability or illness or malnutrition, have high muscle mass (eg, bodybuilders), are an amputee, or have other “non-standard” body composition, are elderly or a child, or are not of European or African-American ancestry, are vegans or vegetarians, or take creatine supplements – then the eGFR using the MDRD equation may not reflect your actual kidney function.
- The Cockroft-Gault equation may be more accurate for adults in the above categories, possibly with an estimated lean mass – that is, your current body minus fat tissue. This may or may not be “ideal” body weight, depending on how much muscle tissue you have.
- The MDRD and Cockroft-Gault equations can also be inaccurate in those with reasonably good kidney function (Stage 1 or 2). The Mayo Quadratic equation is argued to be best in those people.
- The Salazar-Corcoran equation may be more accurate for fat people.
I should also note that doing the equations yourself via online calculators, etc, is just a guide, as pathology labs can take into account known margins of error in their equipment, which varies from lab to lab. This page on renally excreted drug dosing has an overview of some of the above issues. Remember, always check out sources and validity of any information you find, and discuss it with your doctor. Hopefully you have a doctor who is interested in patient collaboration!
Here are some articles and comments discussing the use of eGFR and methods, most of which have references for even more reading:
- The wikipedia article on renal function [*] has descriptions of some of the equations and links to articles on eGFR
- Chronic kidney disease and automatic reporting of estimated glomerular filtration rate: a position statement – Medical Journal of Australia 2005; 183 (3): 138-141
- About eGFR – The Renal Association (UK)
- Modified Glomerular Filtration Rate Estimating Equation for Chinese Patients with Chronic Kidney Disease – Journal of the American Society of Nephrology 17: 2937-2944, 2006
Influence of body weight on the performance of glomerular filtration rateestimators in subjects with type 2 diabetes.
- Influence of body weight on the performance of glomerular filtration rate estimators in subjects with type 2 diabetes (PDF) – Diabetes Care, 2007
- Estimating and Reporting GFR and When not to use the MDRD – National Kidney Disease Education Program
[*] While Wikipedia shouldn’t be used as a primary source, much of the time it provides a good overview of a topic and links to other non-Wikipedia sources. I put a link to the renal function article as it had quite a few eGFR equations included.
There’s a lot of very interesting clinical trials going on a the moment, and most are sounding quite promising. There are 34 listed at clinicaltrials.gov! There are more than ever going on now because a breakthrough discovery was made a few years ago when researchers discovered what makes cysts grow. They examined the fluid from PKD cysts and found that it contained antidiuretic hormone vasopressin, epidermal growth factor, and a lipophilic substance which stimulates the accumulation of cyclic adenosine monophosphate. Source: Therapuetic approaches to ADPKD. So now we know which substances stimulate kidney cells to turn into fluid-filled cysts, and this means we can test out various pharmaceuticals and other things to see if we can stop this overabundance.
We also now know that the hypertension seen in most PKD people is probably caused by cyst growth: the idea is that growing cysts cause ischemia (impaired blood flow) inside the kidney. This makes your kidney think you’ve developed low blood pressure from low blood volume, so it releases renin, a hormone produced in the kidney, which regulates blood pressure among other things. But the rest of your body usually has normal blood flow, so your systemic blood pressure goes up.
This is important to remember when you hear about kidney disease and blood pressure. Uncontrolled hypertension can cause kidney damage for sure, but in PKD people, hypertension is more usually a sign that there is cyst growth. (Which may, in turn, cause further kidney damage, which you really want to avoid.) It’s also why antihypertensive medication that deals with renin seems to work best in those with PKD. Beta blockers aren’t usually recommended in PKD, but calcium channel blockers may be used if the others don’t work well. The PKD Foundation has a good page with information about hypertension in PKD. [Edit: Commenter Kyle has pointed out that beta blockers can in fact act on renin, and may be used in PKD. See the comments for my reasons why I'd come to think they were less useful in PKD.]
So what are some of the main clincial trials using this information? After quite a few trials on rats and mice which showed very promising results for various therapies, human trials are underway. Many people with PKD will have heard of the PKD-HALT study, which is seeing if using two types of anti-hypertensives which act on the renin-angiotensin system will help slow the progression of cyst growth. There’s also the TEMPO 3/4 study which is trialling Tolvaptan, a substance that blocks the vasopressin from ‘sticking’ to the vasopressin receptors. There’s also a trial which is attempting to mimic the diuretic effect of Tolvaptan with consumption of large volumes of water. Another trial is testing if rapamycin/Sirolimus will stop cell proliferation in PKD. Also showing promise are trials of PLX5568 (a drug which hasn’t been named yet); it’s a new protein kinase inhibitor shown to stop cyst growth and reduce kidney volume in animal trials.
Sounds good to me.
There’s a fair bit of talk in patients rights and disability rights activist circles on the nature of charities and foundations that heavily and nearly almost solely promote and fund research towards a cure, versus funding support for people living with illness and disability right now. Duncan Cross has a post titled Don’t Walk, about how he has
some problems with the research/fund-raising agenda most disease organizations pursue.
It’s a thought-provoking read. Where do kidney organisations come in? The PKD Foundation’s stated aim is a cure for PKD. They have a Walk for PKD. They spend most of their money on funding research towards a cure and medical treatments, and a portion on what’s labelled ‘Patient Awareness and Education’. I’m not in much of a position to offer any critical commentary on what the PKD Foundation does as they are a very USA-centric organisation and while there’s an Australian chapter of the Foundation, there’s no online presence so I can’t tell what they do. (I’ll be emailing the convenor soon.) They have local chapters, volunteer-run, throughout the USA and a few other countries, which seem to be patient support groups. I don’t know what they get up to. I’ll find out!
This is not to say that looking for a cure or treatment for any medical condition is a bad thing. It’s not. (I know I’d certainly love a cure for PKD.) It simply becomes problematic when it becomes the locus of funding, research and awareness to the detriment of the patients waiting for a treatment or cure. People need support and advocacy for what’s going on right now, that is, a better quality of life, as well as hope for the future. Awareness campaigns for the general public do tend to focus on how terrible it is to have Disease X and you should Donate Now! so we can cure it. There’s not a lot going on about how you can support people with Disease X in a practical way, right now. Like you know your neighbour has breast cancer or PKD or MS, and donating to related charities can give you a warm fuzzy feeling, but doing something in addition like offering to watch their kids once a fortnight so they can have some time off is going to impact their life much more meaningfully and immediately. This also allows people in different situations to contribute to the cause: someone who’s time-poor may be able to donate some money, someone who’s cash-poor can assist in other ways.
Bill Peckham’s blog, Dialysis From the Sharp End of the Needle, is all about advocacy for dialysis patients. Kidney organisations receive criticism for their emphasis on transplantation as a ‘cure’. The general public tends to believe that once a person with kidney failure receives a transplant, that’s the end of their problems. People with kidney disease either already know better or are sorely disappointed to find out that a transplant may not be quite what they expected. Thus people like Bill Peckham spend a good deal of time and energy on promoting the needs of those on dialysis including personal support networks, and pushing for better funding and recogntion of dialysis techniques and technology.
This patient-to-patient support is becoming increasingly important in the treatment of acute and chronic disease and disability. I’ve already posted about the very interesting white paper on e-patients – and more and more doctors are (finally) realising that the internet is not a hotbed of village idiots eager to self-diagnose and treat themselves with quackery, but an excellent way for people to make contact, discuss the information, studies and research, even produce their own research, discuss what the best treatments are and where to get them, and generally collaborate with others in directing their own health care. This kind of health care hasn’t resulted in scores of deaths through misinformation, as feared. It’s certainly been of help in cases of rare diseases and also ones with a publicity problem. It’s the long tail of health care in action.
Patients along the right-side of the long tail with a niche disease use the extraordinary reach of the web to discover they are not atypical after all. It’s no surprise that patients congregrate around wikis, chat rooms, blogs and social networks to help each other, provide empathy and inspiration. (UBC Health Library Wiki)
I wonder how many of the disease organisations are listening to the conversation that’s happening.
Online communities can be a great source of support and help for those living with illness or disability. So what’s out there for PKD people?
The Polycystic Kidney Disease Foundation has started an online community called Hope Square. It’s in beta at the moment, so go on over, join up and offer your constructive criticism. It looks a little bit like a Ning setup. It’s hard to tell how many members are from what country, but it seems mostly to be people from the USA at the moment from over 700 members total. Resources such as these grow in value the more people join and participate, so it will be interesting to see how it goes.
The Polycystic Kidney Foundation of the UK runs offline support as well as an online group/mailing list via Yahoo Groups: PKD_uk Yahoo Group.
Another Yahoo Group is PKD Care, which averages about 200 messages a month.
There’s a small forum for Europeans: EuroPKDfriends.
The site Daily Strength has lots of groups for all kinds of illnesses, including PKD. PKD @ Daily Strength has nearly 300 members and some moderately active boards.
And there’s quite a few PKD and other kidney-related groups on Facebook. I won’t list them all, just go there and search for polycystic kidney disease.
As for kidney disease resources that aren’t PKD-specific, there’s I Hate Dialysis. And Bill Peckham’s blog Dialysis From the Sharp End of the Needle is also great especially if you’re on dialysis. I’ve found that reading forums and blogs like these has eased the fear of dialysis for me. When the time comes, I’ll be better prepared.
In Australia, we have the Kidney Health Australia organisation, which has a “blog” on the site, which frankly to me looks more like a guestbook than an actual blog, which is a bit weird. They also have YAP Space, which I still haven’t received my approval email for, so I can’t tell you anything about it. Maybe a bit like Hope Square? or more like a regular forum? I know they’re probably just trying to prevent spammers, but having to wait some unknown period of time for an administrator to approve registration is a bit of a turn-away for an online community. People like to get in there and start participating.
There are a few Australian regional support groups but none seem to have an obvious online presence.
If you know of any other online PKD communities, comment and let me know!
I’ll be posting news, information, and other updates on Polycystic Kidney Disease. On Twitter too: follow @PKDnotes for quick updates.
I know the PKD Foundation has a great site including news on PKD, but this blog is from a patient’s perspective. And readers can comment directly on the posts and talk to me via Twitter if they want.
I also consider myself an ‘e-patient‘. I read and research extensively on my medical conditions and avoid doctors who have the old-school ‘Doctor-is-God’ mentality. I prefer to work with doctors who are willing to discuss the research I’ve done and consider what I have to say as valid, and willing to explain something if I’ve got it wrong. Just because I do not have a medical degree doesn’t make me incapable of understanding human biology, nor does it mean it’s acceptable for a doctor to tell me I’m wrong without offering an explanation. I’m well aware of scientific principles and am a skeptical person. I don’t think there’s such a thing as “alternative” medicince, either it’s medicine or it’s not. I’m equally skeptical of the motives of pharmaceutical and medical device companies and the influence they have on clinical researchers, doctors, and public health policy.
The future of medicine and health lies in doctors being willing to take on a collaborative, egalitarian approach to health with their patients. Just as the most successful companies and service providers today are the ones engaging in conversation with their customers online and offline and working with rather than against social networking and information availability, personal service providers must do so too. There will be some people unable or unwilling to take on this very active role in their own health, but those people are probably going to have friends and family who will do so. No longer does a person have to rely on a controlled flow of information from doctors. You are able to go online, read the latest studies and news in peer-reviewed medical journals, search through gigabytes of information, and best of all, connect with other people who have the same health condition as yourself.
There are some doctors who seem deeply apprehensive about patients sharing information on health and doing independent research, largely based around the idea that patients are not able to understand medical concepts, and will self-diagnose and self-treat leading to worsening health, or death. This fear is unfounded, as reported in the e-patients White Paper. Online patient-to-patient health information, such as in forums, social networking sites, and mailing lists was found to be an excellent supplement to primary health care, not a replacement. People are using these online spaces to learn about what the latest research and treatments are, of which busy doctors aren’t always aware. They’re learning who the best doctors are for what conditions, and where the best hospitals are. They’re learning about how to manage their condition day-to-day as well as medications, surgeries, and side effects. An online patient forum in which I participate (non-PKD related) has just produced a paper commenting on the differences between textbook and guidelines, doctor-provided information, and the reality of the particular condition. This is patient empowerment and there is no going back.