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Tuesday, December 8, 2009

Phosphorous Problems

This question comes from Barbara...

My question is what is the highest abnormal phosphorus level that a canine has ever been successfully treated for without total loss of kidney function and maintained on diet & medications. And is there a citable article in any journals?

First, a little bit of explanation on what abnormally high phosphorous levels mean.  There are several things that can cause the phosphorous levels in the blood to increase. The most common reason is for renal (kidney) disease.  As the kidneys fail in their function, phosphorous is retained in the body rather than being expelled.  Other causes can include low parathyroid hormone levels, increased intestinal absorption, acromegaly (a growth disorder), destructive bone lesions, and normal bone growth (mainly in puppies and kittens).  The main thing to keep in mind is that high phosphorous is NOT a disease.  Phosphorous levels don't increase without another reason, and therefore this value is used as an indication of other disease rather than a marker of a specific disorder.

Now let's talk renal disease specifically.  There are numerous reasons why the kidneys may quit functioning, including toxins, genetic tendencies, cancer, and age.  We use several values to assess renal disease, most commonly creatinine, blood urea nitrogen (BUN), and phosphorous.  It is common to have increases in creatininine and BUN with phosphorous remaining normal.  In my experience, if the phosphorous is also eleveated, it indicates a more severe renal insufficiency.  Once the kidneys are damaged, they do not heal.  This fact makes renal failure difficult to treat in pets, and often leads to euthanasia.

Treatment for renal failure is multi-modal.  Special diets are required to help reduce protein stress to the kidney and minimize certain minerals (such as phosphorous).  Fluid therapy may be used to help increase the flushing through the kidneys, helping to prevent build-up of toxic chemicals in the body.  With increased phosphorous levels, medications may be used to bind the phosphoruous and reduce its absorption in the intestines (usually with common antacids!).  Depeding on the cause, other medications may be used to try and more directly treat the underlying problem.

Now back to the question...Barbara, focusing on the phosporous level is not looking at the whole picture.  In your case it sounds like the elevated phosphorous was due to kidney failure.  You need to look at all of the renal values and the urine values and not focus on a single lab value.  If the kidneys are being treated well and phosphate binders are used, the blood phosphorous levels should be controllable.  If the BUN and creatinine are normalized but phosphorous is still high, then more testing is needed to determine why this value is not falling.

The "highest level ever treated" is simply not something that is recorded or even important to doctors.  Journals don't track this data and truthfully it isn't clinically relevant.  Normal phosphorous value can range from 3.0-8.0 depending on the lab or equipment used.  I have seen phosphorous values in the upper teens to low 20s in my own cases.  But truthfully whether a value is 15, 20, 25, or higher doesn't really matter to me.  All of these are significant elevations, and I'm going to treat them all in the same way:  phosphate binders and try to address the underlying cause.  Diagnostic laboratories do keep track of these values to determine what a "normal" range is, but a "highest ever" would be what is statistically called an "outlier" and is insignificant in the analysis of normal ranges.  Therefore these values aren't reported to the profession at large.  Journal articles also don't focus on these extreme values, but instead discuss clinical relevance, especially in the larger picture of the disorder as a whole.  So I hate to say it, Barbara, but your question isn't something that can be answered. 

I hope this at least explains things a little better.  Feel free to ask any follow-up questions.


  1. Dr. Bern: In all these years of medical journals NOT one has addressed a successful case of treating a phosphorus level of 15, 20, or 25? Why do lab work? If normal values are meaningless, why bother?

    Surely at some point a doctor of medicine, says "hey, this is a dying animal?" Thankfully, it happens in human medicine.

    If you do not consider abnormal phosphoru OR calcium levels to indicate the "dying process", what do you go by?

    Thanks for responding,

  2. Barbara, you must not have read my comments carefully, or must have misunderstood. I never said that we don't consider abnormal phosphorous levels. I also never said that we don't address these as signs of serious illness. I never said that I do not consider these abnormal levels related to dying. I never said that normal values were meaningless. And frankly, I'm not sure how you could have thought that I believe that from my comments. Please let me know where I said these things.

    I only said that nobody keeps track of the highest level ever seen. Once a lab value is over a certain point, how high it gets is only important in measuring how much it changes. Also, we are taught "treat the patient, not the lab values". A single lab value is meaningless without taking into account the entire patient and ALL lab values. When journal articles report on cases, it is rare that they address only a single lab value. Case reports are on entire diseases, or how to analyze tests. When we read discussions of renal disease, phosphorous is only a single part of it, and it's poor medicine to ignore the other lab results. As I mentioned in my post, "elevated phosphorous" by itself is meaningless. High phosphorous levels are an indication of disease, not a disease in and of itself. High phosphorous by itself is also not a good marker of impending death. Again, you have to take all values together, and look at the patient as a whole. To doctors (human or veterinary), the "highest level ever seen" is irrelevant to treating the case in front of us and is at most an academic curiosity. Whether the value is "15, 20 or 25" is not going to impact my treatment plan...ALL of these values are elevated! We simply don't do different treatment for a phosphorous of 15 versus a phosphorous of 51 (if such is possible)...not because we choose not to, but because there simply is only limited was to treat it.

    Go back and re-read my post, as you have misunderstood.

  3. Dr Bern: You started the answer very well and thorough, but then ventured off as to a value or values being irrevelant in what the actual "number" is. And what I am saying to you, is there are thresholds that the "body" cannot withstand and return to "normal".

    Is this not a true statement? For example, can a human or animal survive with a 5 hemoglobin indefinitely? I think not. There are limits to what any organ of the body can recover from, including kidneys.

    I did read carefully, but some of the sentences are misleading to the "uninformed", that "upsets" me.

    Perhaps expounding on the calcium/phosphorus ratio would be helpful as to its significance.

    And yes, if you should have a living being with a creatinine & BUN abnormal, with the rest of the values within or near normal, I AGREE, you have a treatable situation.

    Please do clarify with a few details for other readers benefit, and I thank you again for responding.

  4. Ah, that makes a little more sense, Barbara. Thanks for clarifying.

    Yes, there are some lab values that are important at their limits, such as hemoglobin (though hematocrit is probably more accurate to talk about). Another example is platelets. A normal platelet count is around 200-500. However, we don't see spontaneous bleeding until 20 or below. So while 100 is "low" and is a concern, the patient won't start hemorrhaging with this value.

    On the other hand, there are some physiological parameters where this isn't the case, and the kidney values are in this category. I have never seen or heard of an upper limit on BUN, creatinine, or phosphorus. I had a patient one time with a creatinine in the 20s (normal should be no more than a little over 2.0), and it wasn't acting as sick as ones I've seen with half that value. Another example is amylase (a pancreas enzyme). Whether the value is 1000 or 2000, the end result is the same and the patient's clinical picture isn't likely to be different based on this value alone. Also look at alanine transferase (ALT), a liver enzyme. I've seen pets live with a 3-fold increase for years; yet you couldn't easily live with 1/3 of your normal level of red blood cells.

    Now back to your question. The calcium-phosphorous ratio has the most importance in talking about nutrition, not renal disease. The principle is that you should take in at least as much calcium as phosphorous, and probably closer to at least 2:1 calcium:phosphorous ratio. Having an inverted ratio can lead to lack of calcium in the bones and therefore serious orthopedic problems. However, in serious renal failure the high phosphorous can cause too much parathyroid hormone to be released, decreasing calcium in the bones (I'm being a bit simplistic here for the sake of a basic discussion). Phosphorus and calcium deposits in softer tissues can lead to other serious health problems, including muscle pain and heart disease.

    Now again, the absolute upper limit of phosphorus is something that I have never seen or heard of being reported or discussed in any lecture or continuing education discussion on renal disease. It's not the answer that you're looking for, and I'm sorry for that. The lack of this number isn't because vets don't care, it's just that in a clinical treatment that "highest ever" number is really irrelevant. Whether the phosphorus is 10, 30, or 100, we're going to want to do everything we can to bring it down.

    Does that explain it a little better?

  5. Dr. Bern: Yes, you are explaining it more thoroughly, for sure.

    I attempted a simple "pet-owner" version on my blog. Please tell me if you disagree with its premise.

    It is hard to focus on that one value, without the importance and strict body regulation of calcium, acid-base balance, but I tried.

  6. You did a good job overall, Barbara, with just some minor tweaks needed. I commented there.

    As you can see, a summarized discussion of complicated physiology can be difficult. Also, when discussing specific cases, you have to take those textbook or journal discussions and apply them in the patient before you. It's not easy to do in many cases!

  7. Thanks Dr. Bern! I don't know why I thought you were UK??

    But I did not forget the important statement "Blood values: remember to note reference values that vary for methodology)" , I'll change the text so it becomes more prominent.

    It is difficult to separate out the picture into "one component". My original question alluded to the problem: that if the kidneys cannot "bring down" a phosphorus level, it is because function is totally lost and the body has entered a vicious hormonal cycle of PTH, calcitronin pos-neg feedbacks gone awry!

    Back on point, it is one thing to see if blood calcium:phosphorus ratio quickly "corrects" upon treatment, particularly from sl.elevation, but 18 level post 18 hours of bolus fluids? I think it is safe to say "this is looking 99.9% hopeless". (no need to address this)

    I have to restore "my faith" in quality care, that includes diagnostics to aid the "Doctor" in his/her job of diagnosing!

  8. Sorry for missing that statement, Barabara!

    With the few extra details you've provide in this last comment, I completely agree with you. Normally, once you diurese the patient and start to reduce BUN and creatinine, if you're using phosphate binders the phosphorus level should come down pretty quickly. If it doesn't, then I agree that this is what we call a "poor prognostic indicator". It also supports my previous statement that if the other values have normalized but phosphorus remains elevated, we need to investigate why this is staying up. The cascade of events that you described could indeed be a very valid reason. Since BUN and creatinine are values of concentration as much as anything else, these values can change merely by changing concentration: dehydration will increase these values even if the kidneys are normal, and intense fluid therapy will decrease them even if the kidneys are not functioning well. So reducing these values through fluids doesn't mean that you have fixed the kidney disease, only that you have reduced the values by increasing the fluid content in the body.

    I know that it will take a while for your faith to be restored. You have every right to ask many questions of your doctor/vet, and change practitioners if you're not satisfied with the answers!

  9. Dr. Bern, When you address an issue in full as you have, you do restore my faith!

    And not just mine, but the numerous companion owners just like me.

    It is also helpful to remember that sometimes breaking down an issue to simple basics is what reaches the best reasoning of the client.

    People like us (web ring) can be your best advocates because number #1 "we love & want good care for our pets" and #2 we have the patience to bring awareness to other pet-owners , but #3 we need the fine professionals to help too.


  10. Thanks, Barb. I have never doubted that you and your friends want the best and highest quality care for your pet and other people's. I'm also trying to do my own part to increase pet owners' awareness of how to take care of their pets, which is part of the reason for my blog. However, the other reason for my blog is simply to give people some insight into the daily life and thought of veterinarians, and to have a little fun along the way. That's why I don't always take the time to do textbook-level physiological discussions. However, when someone has the interest (such as yourself), I'm happy to go into the details!

    I'm glad for your comments and discussion. As I said to Greg on one of my other topics, I encourage open, civil discussion and debate as a way that we can all learn to understand each other better.


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