Main Functions of the Kidneys

Why CKD Occurs

The Role of the Nephrons

Why CKD Cannot Normally Be Detected At An Early Stage




Tanya's CKD Support Group Now



Site Overview

What You Need to Know First

Alphabetical Index


Research Participation Opportunities

Search This Site



What Happens in CKD?

Causes of CKD

How Bad is It?

Is There Any Hope?

Acute Kidney Injury



Nausea, Vomiting, Appetite Loss and Excess Stomach Acid

Maintaining Hydration

The Importance of Phosphorus Control

All About Hypertension

All About Anaemia

All About Constipation

Potassium Imbalances

Metabolic Acidosis

Kidney Stones



Coping with CKD

Tanya's Support Group

Success Stories



Alphabetical List of Symptoms and Treatments

Fluid and Urinary  Imbalances (Dehydration, Overhydration and Urinary Issues)

Waste Product Regulation Imbalances (Vomiting, Appetite Loss, Excess Stomach Acid, Gastro-intestinal Problems, Mouth Ulcers Etc.)

Phosphorus and Calcium Imbalances

Miscellaneous Symptoms (Pain, Hiding Etc.)



Blood Chemistry: Kidney Function, Potassium, Other Tests (ALT, Amylase, (Cholesterol, Etc.)

Calcium, Phosphorus, Parathyroid Hormone (PTH) and Secondary Hyperparathyroidism

Complete Blood Count (CBC): Red and White Blood Cells: Anaemia and Infection

Urinalysis (Urine Tests)

Other Tests: Ultrasound, Biopsy, X-rays etc.

Renomegaly (Enlarged Kidneys)

Which Tests to Have and Frequency of Testing

Factors that Affect Test Results

Normal Ranges

International and US Measuring Systems



Which Treatments are Essential

Fluid and Urinary Issues (Fluid Retention, Infections, Incontinence, Proteinuria)

Waste Product Regulation (Mouth Ulcers, GI Bleeding, Antioxidants, Adsorbents, Azodyl, Astro's CRF Oil)

Phosphorus, Calcium and Secondary Hyperparathyroidism (Calcitriol)

Miscellaneous Treatments: Stem Cell Transplants, ACE Inhibitors - Fortekor, Steroids, Kidney Transplants)

Antibiotics and Painkillers

Holistic Treatments (Including Slippery Elm Bark)

ESAs (Aranesp, Epogen etc.) for Severe Anaemia

General Health Issues in a CKD Cat: Fleas, Arthritis, Dementia, Vaccinations

Tips on Medicating Your Cat

Obtaining Supplies Cheaply in the UK, USA and Canada

Working with Your Vet and Recordkeeping



Nutritional Requirements of CKD Cats

The B Vitamins (Including Methylcobalamin)

What to Feed (and What to Avoid)

Persuading Your Cat to Eat

Food Data Tables

USA Canned Food Data

USA Dry Food Data

USA Cat Food Manufacturers

UK Canned Food Data

UK Dry Food Data

UK Cat Food Manufacturers

2007 Food Recall USA



Intravenous Fluids

Subcutaneous Fluids

Tips on Giving Subcutaneous Fluids

How to Give Subcutaneous Fluids with a Giving Set

How to Give Subcutaneous Fluids with a Syringe

Subcutaneous Fluids - Winning Your Vet's Support




Heart Problems



Polycystic Kidney Disease (PKD)


Dental Problems









The Final Hours

Other People's Losses

Coping with Your Loss



Early Detection



Canine Kidney Disease

Other Illnesses (Cancer, Liver) and Behavioural Problems

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Home > What is CKD > What Happens in Chronic Kidney Disease



  • This page explains more about the various functions of the kidneys.

  • It is because the kidneys have so many functions that there are so many possible symptoms of CKD. Which ones you might see depends upon which functions are affected.

  • This page also explains why CKD is so common in cats.

  • It discusses why CKD cannot normally be detected until two thirds of function has already been lost.

Main Functions of the Kidneys


The kidneys have five main functions:

  1. the regulation of fluid levels in the body;

  2. the regulation, including filtering and disposal, of waste products in the body;

  3. the regulation of electrolytes (salts in the body's cells which are necessary for survival) in the body;

  4. stimulation of red blood cell production; and

  5. production of renin, which controls blood pressure.

In cats with CKD, as the kidneys become more and more damaged and their ability to function declines, an imbalance can arise in any or all of these areas.  So, for example, a cat whose kidneys struggle with the production of red blood cells will develop anaemia.


Why CKD Occurs


Most cats develop CKD as a result of aging. Studies indicate that around 10% of cats over the age of ten will develop CKD. Older cats are at even greater risk: Chronic Renal Disease in Cats, (1989) in Current Veterinary Therapy X, Krawiec DR & Gelberg HB, Ed. Kirk RW, WB Saunders Company p. 1170-1173 found that 30% of cats over the age of 15 had the disease. A more recent study, Disease surveillance and referral bias in the veterinary medical database (2010) Bartlett PC, Van Buren JW, Neterer M & Zhou C Preventive Veterinary Medicine 94(3-4) pp264–271, found that 28% of the cats over the age of 12 who were examined at four US veterinary hospitals had CKD. Therefore, if you have a cat aged 12-15 or over, s/he has a one in three chance of developing CKD.


Younger cats may also develop CKD but it is less likely. If they are very young (less than two years old), this may be because of a congenital problem. Other possible causes include kidney infections, blockages or exposure to toxins. 


The Cat Doctor mentions that CKD occurs twice as often in Siamese, Maine Coon, Abyssinian, Russian Blue and Burmese cats.


The Causes of CKD page explains more about the various possible causes, but in most cases the treatment will be the same whatever the cause.

Nephrons and Glomerular Filtration Rate (GFR)


The main work of the kidneys is performed by units called nephrons, which filter the blood flowing into the kidneys. The measure of the nephrons’ function is called glomerular filtration rate (GFR).


Khan Academy has a clear video showing how the nephrons work.


Why CKD Cannot Normally Be Detected at an Early Stage


A cat’s kidneys contain around 170,000 - 190,000 nephrons. This is actually many more nephrons than are needed for normal function; plus nephrons can increase their individual function to some extent when other nephrons die. This is why people can donate a kidney and still manage perfectly well with one kidney. In the case of a kidney transplant, if you remove one kidney from the donor, the donor's GFR (glomerular filtration rate, a measure of kidney function) will immediately fall to half of what it was, but will then gradually improve as the remaining nephrons increase their function to compensate for the loss of one kidney. Eventually the nephrons in the remaining kidney will reach almost the same level of function as two kidneys.


It works in a similar way in a cat with kidney disease, i.e. as damaged nephrons die (they are often described as "scar tissue"), other nephrons take over their work. Eventually, however, all the remaining nephrons will be working fulltime (i.e. there will be no "renal reserve" left). It is at this point, when around 66-75% of function has gone, that you will probably start to see symptoms in your cat, as the remaining nephrons start finding it harder to cope with the workload.


This is also why it is actually normal for CKD not to be diagnosed until at least 66% of function has been lost. So please do not feel guilty for not noticing sooner - there was probably nothing for you to notice, plus cats are very good at hiding signs of illness. CKD is not normally painful, so this makes it easier for the cat to hide what is happening. There are a number of possible methods of Early Detection, but some of these are quite specialised, and most people wouldn't know about them; in fact, not all vets are familiar with all of them, although there is a new test (introduced in 2015) which may be helpful called the SDMA test, which is a simple blood test available through IDEXX Laboratories.


Don't waste your energy beating yourself up. What you need to focus on is the fact that cats with CKD can often manage quite well on limited kidney function - for some cats, things only become critical when they have lost as much as 90% of function, and there are  some cats who cope astonishingly well with even less function. So the goal is not to worry about the function that has already been lost, but to try to retain the remaining function for as long as possible, and keep your cat feeling as well as possible. This site aims to help you with both goals.


Links to More Information


Long Beach Animal Hospital clearly explains more about the way the kidneys work.

The Merck Manual explains kidney function (with diagrams).

Cornell University College of Veterinary Medicine has a helpful video overview of feline kidney disease - click on Understanding Kidney Disease.

Kidney Disease is a podcast by Dr Harriet Syme from the Royal Veterinary College which you can download. Scroll down to RVC10.


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This page last updated: 17 August 2015


Links on this page last checked: 17 August 2015






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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