Tuesday, September 17, 2013

Kidney Disease

What are the functions of the kidneys?

The kidneys play a vital role in the body, participating in a number of processes including removing waste products from the body, regulating water balance in the body, regulating calcium and phosphorus levels, and producing certain hormones for the body.  Blood that passes into the kidney is filtered through thousands of small structures called nephrons where waste products are removed and excessive water is released. 

What is chronic kidney disease?

Chronic kidney disease (CKD) is not a singular disease, but more a catch all term for kidneys that are not functioning at full capacity.  The underlying cause for this could include a number of different conditions including:

  • Congenital malformation of the kidneys
  • Chronic bacterial infection of the kidney (pyelonephritis)
  • High blood pressure (hypertension)
  • Diseases of the immune system (i.e. Lupus)
  • Recovery from acute kidney disease (toxin, infection, etc) leading to chronic disease
In many cases we do not figure out the exact cause of kidney insufficiency, but treat the end result.
Signs of chronic kidney disease:
Pets with chronic kidney disease can manifest many different clinical signs including:
  • drinking too much (polydipsia) and urinating large volumes of urine (polyuria)
  • vomiting and/or diarrhea
  • lack of appetite and weight loss
  • general depression related to the elevation of waste products in the blood (uremia)
  • anemia resulting in pale gums and weakness due to a low blood count
  • overall weakness from low blood potassium         
How is chronic kidney disease diagnosed?

If a pet is having clinical signs consistent with kidney disease, then some tests will be recommended to evaluate kidney function.  A combination of blood work and urine evaluation is used to give a good indication of kidney function.  Two blood values are of particular concern when evaluating kidney function (Creatinine and Blood Urea Nitrogen (BUN)).  Elevations in these values could indicate that the kidneys are not functioning well. 

If creatinine elevations are seen, then the urine is also evaluated.  In particular, we are looking at the concentration of the urine.  Normally, the kidneys try to maintain proper water balance in the body.  They do this by reabsorbing water and maintaining it in the body.  When the kidneys are functioning properly they will make more concentrated urine.  If the creatinine or BUN is elevated and there is dilute urine, then this indicates that the kidneys are not functioning properly and may have chronic kidney disease.  There is also a staging system (stage 1-4) to help indicate the degree of damage to the kidneys

FASTED PLASMA CREATININE mg/dl (umol/l)assessed on at least 2 occasions in the stable patient
Absent but patients should be substaged with urine protein creatinine ratio and blood pressure measurements
< 1.4 (<125)
< 1.6 (< 140)
Inadequate urine concentration, renal proteinuria, or abnormal renal architecture based on palpation, imaging, or histopathology
Usually mild or absent but substage as noted above
1.4-2.0 (125-179)
1.6-2.8 (140-249)
As for stage I
Usually present and may be related only to kidneys. Substage as noted above
2.1-5.0 (180-439)
2.9-5.0 (250-439)
As for stage I in addition to clinical signs
Present, but may have extra-renal signs. Substage as noted above
>5.0 (>440)
>5.0 (>440)
As for stage I in addition to clinical signs

Other changes on blood work and urine could include:
  • Non- regenerative anemia
  • Increased phosphorus
  • Low potassium levels
  • Calcium is often normal but can be elevated in some pets with CKD and rarely is decreased
  • Protein or bacteria in the urine
Other tests may also be recommended including:
  1. Abdominal radiographs (x-rays) or ultrasound to evaluate kidney size
    What might this test show?  The kidneys in pets with CRD are usually small reflecting the death of a large number of nephrons. If the kidneys are large then certain causes for the CKD should be considered such as lymphoma (cancer) of the kidneys, or an uncommon disease called amyloidosis. Some pets with signs of kidney disease who have large or normal sized kidneys may have acute kidney failure rather than CKD. The treatment and prognosis for pets with acute kidney disease differs from the treatment and prognosis of pets with CKD.
  2. Bacterial culture
    What might this test show?  Bacterial infection is not a common cause of CKD but pets with CKD may develop a bacterial infection as several aspects of the pet's immune system may be less functional when the kidneys are failing.  If white blood cells are observed on microscopic examination of the pet's urine, a bacterial culture of the urine should be obtained.
  3. Urine protein/creatinine ratio
  4. Blood pressure
What are the treatment options for my pet?

Unfortunately, chronic kidney disease is a progressive disease and is not curable.  However, there are many options available to help treat symptoms and signs associated with kidney disease.  There is no treatment combination that is standard for every pet and many times incremental addition to medications is needed as the disease process progresses.  In some cases, pets may need to be hospitalized for a period of time to replenish fluids and in other cases pets are sent home with conservative treatments.  I will list treatment options available, but remember that an individual pet may not need all these treatments.

  • Diet modification:  Studies have shown that pets switched to a protein restricted (high quality protein), phosphorus restricted diet have a higher quality of life, fewer uremic crises, and may live longer than pets fed a regular maintenance diet.  There are many commercially available, prescription diets that meet these standards. 
  • Phosphorus binders: Even with phosphorus restricted diets some pets still have elevated phosphorus levels.  In these cases, supplements can be added to the food that help bind more phosphorus and restrict levels even more
  • Hypertension medications: High blood pressure often accompanies kidney disease and can lead to further damage to the kidneys.  Monitoring for hypertension and adding anti-hypertensive medications (amlodipine, ACE inhibitors) when present may be warranted in some pets.
  • Stomach protectors: Build-up of uremic toxins can lead to stomach upset and inappetence.  Protecting the stomach lining with medications that lower the acidity of stomach contents can be helpful.  Medications can include antacids (famotidine or ranitidine), protein pump inhibitors (omeprazole), or stomach lining medications (sucralfate).
  • Anti-nausea medication: Pets may also be inappetent because of nausea.  Cerenia or metoclopramide are examples of anti-nausea medications.
  • Omega 3 fatty acids: Supplementing with fatty acids has been shown in some studies to improve survival in pets
  • Anemia medications: The kidneys produce a hormone called erythropoietin that signals the bone marrow to make more red blood cells.  With kidney disease, this hormone may be depleted, so anemia develops in patients.  There are commercially available erythropoietin supplements that can be given to increase red blood cell counts.  Pros and cons of this medication should be discussed prior to starting the medication.
  • Fluid supplementation: Since diseased kidneys are unable to concentrate urine properly, a pet will lose an excessive amount of water in the urine.  Making sure that water is always available and promoting water consumption is important.  In cases where a pet is not keeping up with fluid loses, either periodic subcutaneous fluids (can be done at home) or intravenous fluids may be necessary.
  • Potassium supplementation: Excessive potassium is lost with diseased kidneys, which can lead to loss of energy.  Adding a potassium supplement may be needed.
  • Calcitriol: Calcitriol is the active form of vitamin D and helps with regulation of calcium and phosphorus.  It is produced in the kidney, so may be decreased in patients with chronic kidney disease.  To help combat renal secondary hyperparathyroidism, calcitriol may be instituted.  Careful and periodic monitoring of calcium and phosphorus levels is recommended. 

As discussed earlier, not every pet needs every treatment and your veterinarian will evaluate blood work and clinical signs before recommending certain treatments.  Also, some pets are more amenable to treatment (especially in the case of cats) as multiple medications may be needed in a day.  Individual owner circumstances can also dictate how aggressive treatment might be.  With cats, combining multiple medications into a single gel cap may be easier than administering multiple medications at a time.

Goal of therapy:

As chronic kidney disease is not curable, our goal is to provide a good quality of life as long as we can.  Some owners may elect to only change the diet in response to diagnosis, whereas others may add as many medications as reasonable and possible to help their pet.  The goal is to find the right balance for both the owner and the patient.  With proper care some pets with early kidney disease can still live a great quality of life for years.

For more information from the perspective of an owner please visit http://www.felinecrf.com.