Diagnosis

Diagnosis of CKD

CKD diagnosis is based on three diagnostic methods: clinical examination, laboratory analysis of blood and urine, and imaging techniques such as X-rays and ultrasound. Diagnosis is based on the cumulative findings of all techniques.

The International Renal Interest Society (IRIS) publishes guidelines for classifying chronic kidney disease (CKD) into four stages. These precisely define which parameters should be determined and which parameters are indicative of particular stages (“staging= Classification of the cat into a stage of chronic kidney disease according to IRIS...” is classification of an affected cat into a specific CKD stage on the basis of the given criteria). Blood pressure and proteinuriaIncreased protein in urine, leading to loss of protein. Normally, only a very small amount of protein is excreted in the urine. In chronic kidney disease, the amount lost may increase. High blood pressure damages blood vessels in the nephrons making them more permeable and... are also taken into account. The most important factors for classification are the level of creatinineCreatinine is a breakdown product of muscle metabolism. Its blood level is dependent, among many factors, on age, weight, nutritional status and muscle mass. Hence, creatinine levels in the blood vary from individual to individual. Creatinine is continuously excreted in the urine. Increased blood creatinine... in the blood and the “SDMASDMA = Symmetrical Dimethylarginine, which is a degradation product of the amino acid arginine and is excreted solely through the kidneys. SDMA is a highly specific biomarker for kidney function in cats. Read more: SDMA test (blood test)... test” (→ see Blood tests). To date, the most important criterion for CKD evaluation has been the level of creatinine in the blood. Levels of ureaUrea is the nitrogen-containing breakdown product of protein metabolism. The nitrogen from the proteins is converted to ammonia in the liver, which is combined with carbon dioxide to form urea. This is continuously excreted via the kidneys but also via sweat. Urea is one of... and phosphate in the blood are also important in CKD diagnosis.

1. Clinical examination

Cats are examined to determine their general condition, age, sex, breed, pre-existing conditions, medication and acute health problems. Their temperature is then measured, the visible mucous membranes are examined for paleness and they are examined for dehydrationA deficit of total body water. Dehydration can be caused by excessive fluid loss, for instance via the kidneys in CKD, or by insufficient fluid intake...., emaciation, bad breath and eye health. Usually the vet will also feel for their kidneys (kidney palpationUsing touch to check sites and organs of an animal’s body to diagnose disease. Palpation is part on a clinical examination....) and examine them for pain, size and palpable superficial changes. Symptoms are the main focus.

Weight loss with CKD

The cat will usually be weighed during the routine examination. It may be noticeable that the cat has lost weight in recent months. A 2016 study showed that CKD cats had already lost about 10% of their weight 1 year before diagnosis.  For a 4.5kg cat this is about 450g. A weight loss of 5% in 3-4 months can be a first sign of possible disease.

CKD cats lose weight because they may have an increased energy requirement and also because they digest amino acids more poorly and their appetite decreases (s. Amino acid dilemma). The Body Condition Score (BCS) and Muscle Condition Score (MCS) are very helpful in assessing weight and muscularity.

The Body Condition Score (BCS) is determined by visual inspection and palpation of the cat’s body. There are 9 scale levels, which vary according to the amount of fat in the cat, particularly around the ribs, waist and abdomen. Underweight cats are scored 1-3, normal or ideal weight cats are scored 4-5 and overweight cats are scored 6-9. Cats with a BSC of 4-6 are well positioned for CKD as studies have shown that normal or slightly overweight cats have a higher chance of surviving CKD and therefore live longer.

The Muscle Condition Score (MCS) is used to look more closely at a cat’s muscularity. The four-level classification distinguishes between normal muscularity and three levels (mild, moderate, severe) of muscle wasting. Grading is based on palpation of the back muscles along the spine, the shoulder and back of the head muscles, and the pelvic muscles. Muscle wasting may be associated with a condition such as chronic kidney disease and/or hyperthyroidism. However, a decrease in muscle mass is generally expected in older cats.

2. Laboratory tests

2.1 Blood tests to diagnose CKD

• Creatinine
• SDMA test
• Urea
• Phosphate
• Indoxyl Sulphate

2.2 Urine analyses

• Specific gravity (SG) of urine
• Urinary protein levels (UPC)
• Cystatin-B

2.3 Further blood tests

• Calcium
• Calcium and sodium
• ErythrocytesErythrocytes are red blood cells and contain the blood pigment haemoglobin. Red blood cells are responsible for transporting oxygen from the lungs into the cells of the tissues. They are predominantly produced in the bone marrow of larger bones.... and haematocrit
• Glomerular filtration rateThe glomerular filtration rate (GFR) is defined as the volume of fluid that is filtered by the glomeruli of the nephrons of both kidneys per unit of time to produce primary urine. It is, therefore, the chief measure of kidney function. The rate corresponds to... (GFR)

3. Further tests

3.1 Radiological tests

• X-ray
• Ultrasound
• CT and MRI

3.2 Measurement of blood pressure