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.