Testing for Weight Loss in Cats

What might be causing my cat’s weight loss?

Weight loss can be due to simple problems of feeding and nutrition, or can be due to a variety of medical conditions that result in poor digestion, decreased absorption of nutrients, or loss of nutrients from the body.

Dietary problems. Weight loss occurs when a cat’s diet does not contain enough energy to meet the body’s needs. This could mean the cat just is not getting enough to eat or is eating a poor-quality food, but it could also mean that the cat has unusually high energy requirements such as rapid growth, pregnancy, or intense physical activity.

For example, young active kittens need extra energy and specific nutrients for growth and development; they could easily be underweight if fed an adult diet only. Any pet fed a low-quality diet could be at risk for weight loss due to incomplete nutrition or poorly digestible ingredients. Your veterinarian can give you guidelines about the best food for your cat and how much to feed.

Disorders and medical conditions. These include difficulties chewing and swallowing food, diseases such as hyperthyroidism, parasites, infectious diseases, cancer, and disorders of the kidney, heart, liver, pancreas, or intestines.

How do you determine the cause of weight loss in a cat?

Finding the cause of a cat’s weight loss usually starts with a complete history and physical examination. A cat’s history of illness includes details about the quantity and quality of food being fed, changes in appetite and activity, changes in thirst or urination, and other signs of illness such as vomiting or diarrhea, and so on.

Physical examination involves checking the entire cat, listening to the heart and lungs with a stethoscope, and palpating the abdomen (gently squeezing or prodding the abdomen with the fingertips to identify abnormalities inside the body). A complete physical examination may give clues about the cause of the weight loss; for example a kitten with a “pot-bellied” appearance may have intestinal parasites; an elderly cat with a mass in the neck region could have thyroid disease.

The cause of the weight loss may not be clear on physical examination and your veterinarian may recommend doing screening tests. These are a series of simple tests that provide information about the overall health of your cat and may provide further clues about the underlying problem. In a cat with weight loss, the most common screening tests would include complete blood count (CBC), serum biochemistry profile, urinalysis, parasite testing, and evaluation of thyroid hormones. Based on the results of these screening tests, additional specific tests may be recommended.

What might these screening tests indicate?

A) Complete blood count. This is a simple blood test that provides information about the different cell types in blood. These include red blood cells, which carry oxygen to the tissues, white blood cells, which fight infection and respond to inflammation, and platelets, which help the blood to clot. The CBC provides details about the number, size, and shape of the various cell types, and identifies the presence of abnormal cells in circulation. See handout “Complete Blood Count” for further information.

In a cat with weight loss, examples of changes seen on a CBC could include:

• Anemia. This means the number of red blood cells and the amount of hemoglobin in the blood are lower than normal. Anemia can be found with many diseases, including those associated with weight loss such as intestinal parasites, intestinal bleeding, Addison's disease, liver disease, kidney disease, and cancer.
• Changes in the appearance of red blood cells. For example, small, pale red blood cells suggest iron deficiency, which could indicate poor nutrition, parasitism, intestinal bleeding, or any chronic blood loss.
• Increased numbers of white blood cells. This could suggest underlying inflammation the presence of infectious disease or rarely cancer.
• Unusual white blood cells. The presence of atypical or unusual white blood cells might indicate underlying bone marrow disease or cancer.

B) Serum biochemistry. This is the chemical analysis of serum, which is the pale yellow liquid part of the blood that remains after the cells and clotting factors have been removed. There are many substances in serum, including proteins, enzymes, fats, sugars, hormones, electrolytes, etc. Measuring the levels of the various substances in the blood provides information about the health of the body’s organs and tissues such as the liver, kidney, and pancreas, and helps to detect diabetes. See handout “Serum Biochemistry” for further information.

Some examples of changes in a serum biochemistry profile that might help explain weight loss in a cat could include:

• Abnormally high levels of the liver-related enzymes alanine aminotransferase (ALT), alkaline phosphatase (ALP), and gamma glutamyltransferase (GGT) are associated with liver damage.
• Mildly increased levels of liver-related enzymes could signal hyperthyroidism.
• Increased blood glucose could be a sign of underlying diabetes mellitus or “sugar” diabetes.
• Increased kidney values suggest kidney disease.
• Low albumin (a blood protein) is associated with various conditions that cause weight loss including liver failure, kidney disease, blood loss, intestinal disease, liver shunts, pancreatic insufficiency, and more.
• Altered electrolytes. Electrolytes are salts and minerals found in the blood. Changes in electrolytes can indicate underlying kidney disease, endocrine (hormonal) disease, malnutrition, or cancer. 

C) Urinalysis is a simple test that analyzes the physical and chemical characteristics of urine. It measures how well the kidneys are working, identifies inflammation and infection in the urinary system, and helps to detect diabetes and other metabolic disturbances. Urinalysis is important in any sick animal and is necessary for the proper interpretation of the serum biochemistry profile, especially in a cat that has kidney disease or diabetes. See handout “Urinalysis” for further information.

In a cat with weight loss, examples of changes seen on urinalysis could include:

• Increased amounts of protein which is associated with kidney disease and indicates that protein is being lost from the body.
• Blood which indicates bleeding from the kidneys or urinary system.
• White blood cells and white blood cell casts (tubular-shaped clusters of white blood cells) suggests bacterial infection of the kidneys.
• Large amounts of glucose indicate that diabetes mellitus is likely present.

D) Parasite tests. Having intestinal parasites, or “worms,” is a common cause for weight loss, especially in kittens. Testing a fresh stool sample for parasite eggs is an important screening test, and a simple fecal flotation is often the first test done. This involves taking a small sample of fresh stool and mixing it with a solution that causes the parasite eggs to float to the top of the sample. The eggs are collected and examined under the microscope to determine which parasites are present and how many there might be. See handout “Fecal Flotation” for further information. There are many other tests for parasitism and your veterinarian may recommend additional testing.

E) Serum thyroxine (total T4). This test is used to diagnose hyperthyroidism in cats (see handout "Hyperthyroidism in Cats" for further information). Hyperthyroidism is a common disorder in older cats and is caused by an overactive thyroid gland. The gland produces excessive amounts of thyroid hormones, which substantially increases the body’s metabolic rate and leads to weight loss. Most cases of hyperthyroidism can be diagnosed with a single blood test that measures the level of total thyroxine (T4) in the blood stream. Affected cats typically have markedly elevated levels of T4 in their blood.

What additional tests might be recommended to investigate weight loss?

The need for additional testing will depend on the history, physical examination, and the results of the initial screening tests. Given the many causes of weight loss, there is an equally long list of possible tests. A few of the more common specialized tests would include:

• Viral testing for feline leukemia virus or feline immunodeficiency virus.
• ACTH stimulation test to confirm Addison's disease (found more often in dogs than cats).
• Serum fructosamine to confirm diabetes mellitus (sugar diabetes).
• Serum trypsin-like immunoreactivity test if decreased pancreatic function is suspected.
• Serum bile acid test to assess liver function.
• Urine protein/creatinine ratio to determine if there is substantial urinary protein loss.
• Radiographs (X-rays) or ultrasound to look for tumors and to evaluate the organs of the chest or abdominal cavity.
• Fine needle aspiration or other biopsy techniques to investigate tumors or enlarged organs.
• Testing for heart disease including heartworm test, imaging, ProBNP blood test, electrocardiogram, etc. if abnormalities in heart size, rate, rhythm, or sounds are identified.
• Testing for specific infectious diseases.