Phosphorus - Test1

Tanya's Comprehensive Guide to
Feline Chronic Kidney Disease
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Phosphorus

Prolonging Life
Page Summary
Measuring Phosphorus and Target Blood Phosphorus Levels
Summary of Phosphorus Goals
Ways to Control Phosphorus Levels

      
Overview

      
  • If your cat's blood phosphorus level is over 6 mg/dl (USA) or over 1.9 mmol/L (international), it is too high and you need to get it under control.
                 
  • Keeping phosphorus levels under control can help slow the progression of the CKD, reduce the risk of serious problems and make your cat feel better.     
  •         
  • Feeding a food low in phosphorus is the first and best step. Ideally you want a food with a level below 0.5% phosphorus on a dry matter analysis basis. Therapeutic kidney diet foods are the only complete foods which meet this criterion.

  • If your cat will not eat the therapeutic kidney diet, feeding a food as low in phosphorus as possible and adding a phosphorus binder to the food when appropriate can help control your cat's phosphorus levels.     
          
Please also visit the Phosphorus Binders page.
Why High Phosphorus Levels Matter

            
Phosphorus is a mineral essential for good health which is contained in many foods. The body is very good at regulating its phosphorus levels by removing excess phosphorus via the kidneys. However, the kidneys of a CKD cat can no longer efficiently excrete excess phosphorus, so the vast majority of CKD cats will develop levels of phosphorus in their blood that are too high: this is known as hyperphosphataemia.       
                          
In contrast to the protein debate, there is no dispute about the importance of treating hyperphosphataemia because of the problems it causes. Indeed, an update on the Western Veterinary Conference 2017 reports that "phosphorus restriction may be the "single most powerful treatment," according to Dr. Chew."

High phosphorus levels may:
Make the Cat Feel Unwell

High phosphorus levels can cause a variety of unpleasant symptoms and generally make a CKD cat feel quite unwell. There is a list of possible symptoms below.
Cause CKD Progression
High phosphorus levels can make CKD progress more quickly. A human study, Serum phosphate and mortality in patients with chronic kidney disease (2010) Eddington H, Hoefield R, Sinha S, Chrysochou C, Lane B, Foley RN, Hegarty J, New J, O'Donoghue DJ, Middleton RJ & Kalra PA Clinical Journal of the American Society of Nephrology 5(12) pp2251-2257, found that the risk of dying for patients in stages 3 and 4 was higher if they had higher phosphorus levels, even if the phosphorus was technically within normal range. A study of cats, Survival in cats with naturally occurring chronic kidney disease (2000-2002) (2008) Boyd LM, Langston C, Thompson K, Zivin K & Imanishi M Journal of Veterinary Internal Medicine 22(5) pp1111-7, found that there was an 11.8% increase in the risk of death for every one mg/dl increase in phosphorus in the cat's blood.

Survival of cats with naturally occurring chronic renal failure: effect of dietary management (2000) Elliott J, Rawlings JM, Markwell PJ, Barber PJ Journal of Small Animal Practice 41(6) pp235-242, found that the cats who ate reduced phosphorus food or food with added phosphorus binders lived more than twice as long as those who did not.

The role of phosphorus in the pathophysiology of chronic kidney disease (2013) Geddes RF, Finch NC, Syme HM, Elliott J Journal of Veterinary Emergency & Critical Care (San Antonio) 23 pp122-133 reports that a phosphatonin called fibroblast growth factor 23 (FGF-23) "is now considered to be a key regulator of plasma phosphorus concentration in people" and states that the role of FGF-23 in companion animals with CKD is also being investigated. Early Detection briefly discusses the role FGF-23 may play in the early detection of CKD.

Laboratory evaluation in dogs and cats with chronic kidney disease (2015) Grauer GF Clinician's Brief May 2015 pp65-69 states "Tighter control of hyperphosphatemia, renal proteinuria, and systolic hypertension may improve treatment outcome."
Cause Secondary Hyperparathyroidism
Elevated phosphorus levels can adversely affect calcium levels and eventually can trigger problems with a hormone called parathyroid hormone (PTH), causing a serious condition called secondary hyperparathyroidism (which is not the same thing as hyperthyroidism, although Cornell University College of Veterinary Medicine does mention that around 20% of cats with hyperthyroidism also have elevated phosphorus levels).

Chronic kidney disease (CKD) in dogs and cats — staging and management strategies (2015) Chew D Presentation to the Virginia Veterinary Medical Association 2015 Virginia Veterinary Conference states that it is possible for a CKD cat to develop secondary hyperparathyroidism even if phosphorus levels and ionised calcium levels are normal. He explains "In the early stages of chronic kidney disease increased levels of parathyroid hormone (PTH) keep serum phosphorous within the normal range by increasing phosphate excretion into urine. This allows for normalization of serum phosphorous at the expense of hyperparathyroidism." Therefore, even a cat with normal phosphorus levels but with elevated PTH levels would benefit from phosphorus restriction.

Relationship among serum creatinine, serum gastrin, calcium-phosphorus product, and uremic gastropathy in cats with chronic kidney disease (2014) McLeland SM, Lunn KF, Duncan CG, Refsal KR & Quimby JM Journal of Veterinary Internal Medicine 28(3) pp827-37 compared CKD cats with healthy cats. They found that "The high incidence of fibrosis and mineralization among cats with CKD suggests that more aggressive management of hyperphosphatemia and renal secondary hyperparathyroidism should be considered."
Reduce Response to Anaemia Treatment
High phosphorus levels may reduce the cat's response to ESAs, a treatment used for severe anaemia, which is relatively common in CKD cats.
     
           
Symptoms of Hyperphosphataemia

              
There are a number of different symptoms of high phosphorus levels. You may not see all of these symptoms, and some of them may have other causes as outlined under each symptom. However, if you see any of the symptoms described below, please ensure that your cat's phosphorus level is checked (via bloodtests) and is no higher than 6 mg/dl (US) or 1.9 mmol/L (international).

     
     Loss of Appetite
     
           
High phosphorus levels can make a cat feel bad and lead to a loss of appetite, particularly if secondary hyperparathyroidism develops.

Other causes include levels of toxins in the blood which may cause excess stomach acid, anaemia, crashing, metabolic acidosis, mouth ulcers, fluid build-up, the use of antibiotics, constipation or the use of medication for hyperthyroidism. Dental problems may also cause loss of appetite.

Cats who do not eat are at risk of developing a potentially life-threatening condition known as hepatic lipidosis; Mar Vista Vet has more information about this. Therefore, it is important to try to find the cause and treat it as quickly as possible.

     
Itching
     
           
Itching is fairly common in cats with high phosphorus levels, particularly if the high phosphorus levels go untreated, resulting in secondary hyperparathyroidism.

Itching may also be caused by general levels of toxins in the blood. Alternatively itching may indicate a vitamin B deficiency or be a sign of an essential fatty acids deficiency. Itching on the face in particular may be a side effect of medication for hyperthyroidism. Occasionally itching can be a sign of liver problems; if this is the case, your cat's bloodwork should show elevated liver values.

     
            Lack of Co-ordination in the Limbs/Back Leg Weakness
     
           
This can be due to high phosphorus levels interfering with the nerve messages that control the limbs, a condition known as neuropathy. Some of the symptoms include "forgetting" where the hind legs are (getting up and leaving without them, for instance, or leaving them in the air after licking them), or stumbling and feet crossing over when walking.

     
     Plantigrade Posture
     
           
You may also see a plantigrade posture (as demonstrated by Ollie to the left), where the cat walks on his/her hocks instead of his/her feet: this is most common in diabetic cats, but may sometimes be seen in cats with high phosphorus levels, or with neurological problems from other causes. Ollie did this because of low potassium levels.

Long Beach Animal Hospital has a photograph of a cat with diabetic neuropathy doing this (click on Symptoms). Newman Veterinary has a good before and after photo of a diabetic cat with this problem, scroll down a little to Other Common Consequences, then click on Plantigrade Stance (in red font).

University of Chicago Center for Peripheral Neuropathy is a human site which discusses uraemic neuropathy (neuropathy caused by CKD).

     
Teeth Grinding
     
           
If your cat's high phosphorus levels go untreated, your cat may eventually develop a condition called secondary hyperparathyroidism. One symptom of secondary hyperparathyroidism is "rubber jaw", which may present as teeth grinding.

Other more common causes of teeth grinding include excess stomach acid, dental problems and dehydration.

Animal Dentistry and Oral Surgery Specialists discuss the various courses of teeth grinding in cats.

Youtube has a video of a cat grinding his/her teeth.

     
Knuckling
     
           
"Knuckling" may also be seen, where the cat walks on the top of the foot with the toes tucked underneath, appearing almost to be dragging the toes behind. I haven't been able to find a photo of a cat with high phosphorus levels doing this, but there is a video on youtube of a dog with a similar problem (but with a different cause).
     
Weakness
     
           
Weakness and muscle wasting may be seen, especially in the back legs. This can be caused by high phosphorus levels leading to secondary hyperparathyroidism.

Weakness in the back legs is often caused by low potassium levels or occasionally by low magnesium or low calcium levels; while muscle wasting may be caused by metabolic acidosis. General weakness may be caused by anaemia. If your cat no longer jumps, this may be thought to be weakness when in fact it is an unwillingness to jump because of blindness caused by hypertension. An inability to jump or climb may also be caused by arthritis.

If your cat suddenly cannot walk properly on one leg, particularly a back leg, and the leg feels cold to the touch, this may indicate a heart-related problem known as an arterial thromboembolism. This is a medical emergency, and you need to contact your vet as soon as possible.

Weight Loss
     
           
This may be caused by high phosphorus levels.

Other causes include proteinuria or  metabolic acidosis. Weight loss may also be a symptom of other diseases such as diabetes or hyperthyroidism. Other possible causes include IBD (Inflammatory Bowel Disease) or cancer.

The World Small Animal Veterinary Association has a body condition score chart showing how to gauge your cat's physical condition.
     
Nausea
     
           
High phosphorus levels and secondary hyperparathyroidism it may cause may result in nausea, which may be manifested as a lack of appetite.

Anaemia or metabolic acidosis may also cause nausea.  

Twitching, Trembling or Shaking
     
           
Twitching may be caused by high phosphorus levels.

Other possible causes of twitching in CKD cats include:

  • low or high potassium levels
  • high toxin levels (uraemia)
  • high blood pressure
  • calcium imbalances (especially head twitching)
  • hyperthyroidism
  • Vitamin B deficiency
  • maropitant (Cerenia) for nausea

If your cat only twitches while you are giving fluids, it is probably caused by either the type of fluid used or by giving cold (room temperature) fluids but make sure your cat is not being overhydrated.

Pharaoh's Shakes is a video showing a CKD cat twitching.

Pet MD mentions that twitching may be caused by kidney disease.


Loss of Appetite                         

High phosphorus levels can make a cat feel bad and lead to a loss of appetite, particularly if secondary hyperparathyroidism develops.

Other causes include levels of toxins in the blood which may cause excess stomach acid, anaemia, crashing, metabolic acidosis, mouth ulcers, fluid build-up, the use of antibiotics, constipation or the use of medication for hyperthyroidism. Dental problems may also cause loss of appetite.

Cats who do not eat are at risk of developing a potentially life-threatening condition known as hepatic lipidosis; Mar Vista Vet has more information about this. Therefore, it is important to try to find the cause and treat it as quickly as possible.
Itching                                       

Itching is fairly common in cats with high phosphorus levels, particularly if the high phosphorus levels go untreated, resulting in secondary hyperparathyroidism.

Itching may also be caused by general levels of toxins in the blood. Alternatively itching may indicate a vitamin B deficiency or be a sign of an essential fatty acids deficiency. Itching on the face in particular may be a side effect of medication for hyperthyroidism. Occasionally itching can be a sign of liver problems; if this is the case, your cat's bloodwork should show elevated liver values.


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TREATING YOUR CAT WITHOUT VETERINARY ADVICE CAN BE EXTREMELY DANGEROUS.

I have tried very hard to ensure that the information provided in this website is accurate, but I am NOT a vet, just an ordinary person who has lived through CKD with three cats. This website is for educational purposes only, and is not intended to be used to diagnose or treat any cat. Before trying any of the treatments described herein, you MUST consult a qualified veterinarian and obtain professional advice on the correct regimen for your cat and his or her particular requirements; and you should only use any treatments described here with the full knowledge and approval of your vet. No responsibility can be accepted.
 
If your cat appears to be in pain or distress, do not waste time on the internet, contact your vet immediately.

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