Testing for Weight Loss in Dogs

By Krista Williams, BSc, DVM, CCRP; Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant BSc, DVM, DVSc

What might be causing my dog’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 whenever a dog’s diet does not contain enough energy to meet the body’s needs. This could mean the dog just is not getting enough to eat or is eating a poor-quality food, but it could also mean that the dog has unusually high energy requirements such as rapid growth, pregnancy, or intense physical activity. For example, young active puppies need extra energy and specific nutrients for growth and development; they could easily be underweight if fed an adult diet only. Similarly, an active hunting dog with high energy needs would need to eat more food than a leash-exercised dog to maintain good body weight. Any dog 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 and how much to feed your dog.

Disorders and medical conditions. These include difficulties chewing and swallowing food, diseases such as Addison's disease, 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 dog?

Finding the cause of a dog’s weight loss usually starts with a complete history and physical examination. A dog’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.

"Finding the cause of a dog’s weight loss usually starts with a
complete history and physical examination."

Physical examination involves checking the entire dog, 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 puppy with a “pot-bellied” appearance may have intestinal parasites; a dog with abnormal heart or lung sounds may have heart 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 pet and may provide further clues about the underlying problem. In a pet with weight loss, the most common screening tests would include complete blood count (CBC), serum biochemistry profile, urinalysis, and parasite testing. 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 dog 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 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 profile. 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."

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 on a serum biochemistry profile that might help explain weight loss in a dog 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.
  • 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, especially sodium and potassium, are often seen with Addison's disease, which is a disorder associated with weight loss.

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 pet that has kidney disease or diabetes.

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

  • Increased amounts of protein, which is associated with kidney disease, 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 very young puppies. 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.

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:

  • ACTH stimulation test to confirm Addison's disease.
  • Serum fructosamine to confirm diabetes mellitus. This test is more frequently performed in cats than dogs.
  • 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, if abnormalities in heart size, rate, rhythm, or sounds are identified.
  • Testing for specific infectious diseases.
Related Articles