What could be causing my dog’s weight loss?
Weight loss can be due to simple problems of feeding and nutrition, or it 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 dog’s diet does not contain enough energy to meet the body’s needs. The dog may not be getting enough to eat, or it could be eating poor-quality food, or it could have 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 to eat more food than a leash-exercised dog to maintain a good body weight.
Any dog fed a low-quality diet could be at risk of weight loss due to incomplete nutrition or poorly digestible ingredients. Your veterinarian can give you guidelines about the best food for your dog and how much to feed.
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 gastrointestinal tract.
How do you determine the cause of weight loss in a dog?
To find the cause of a dog’s weight loss, your veterinarian will usually start with a complete history and physical examination. A history 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.
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 after physical examination and your veterinarian may recommend doing screening tests. These simple tests provide information about the overall health of your dog and may provide further clues about the underlying problem.
In a dog 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 can screening tests indicate?
Complete blood count (CBC). This simple blood test provides information about the different cell types in the blood. These cell types 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.
In a dog with weight loss, changes seen on a CBC could include:
- Anemia. With anemia, the number of red blood cells and the amount of hemoglobin in the blood are both lower than normal. Anemia occurs 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. Changes can provide information. 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. More white blood cells could suggest underlying inflammation, the presence of infectious disease, or possibly cancer.
- Unusual white blood cells. The presence of atypical or unusual white blood cells might indicate underlying bone marrow disease or cancer.
Serum biochemistry profile. Serum is the liquid part of blood that remains after the cells and clotting factors have been removed. Serum biochemistry is the chemical analysis of serum. There are many substances in serum, including proteins, enzymes, fats, sugars, hormones, and electrolytes. Measuring levels of these 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.
Some examples of changes in 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-glutamyl transferase (GGT) are associated with liver damage.
- Increased blood glucose could be a sign of underlying diabetes mellitus (“sugar” diabetes).
- Increased kidney values suggest kidney disease.
- Low albumin (a blood protein) is associated with conditions that cause weight loss, including liver failure, kidney disease, blood loss, intestinal disease, liver shunts, and pancreatic insufficiency.
- Changes in electrolytes, especially sodium and potassium, are often seen with Addison’s disease, which is a disorder associated with weight loss. Electrolytes are salts and minerals found in the blood.
Urinalysis. 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 to properly interpret the serum biochemistry profile, especially in a pet that has kidney disease or diabetes.
In a dog with weight loss, examples of changes seen in a urinalysis could include:
- Increased amounts of protein indicate that protein is being lost from the body, which is associated with kidney disease.
- Blood indicates bleeding from the kidneys or urinary system.
- White blood cells and white blood cell casts (tubular-shaped clusters of white blood cells) suggest bacterial infection of the kidneys or urinary system.
- Large amounts of glucose indicate that diabetes mellitus is likely present.
Parasite tests. Intestinal parasites (“worms”) are a common cause of weight loss, especially in 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. For this test, a small sample of fresh stool is mixed 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. 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 results of the initial screening tests. Given the many possible causes of weight loss, there is an equally long list of possible tests. A few of the more common specialized tests would include:
- Testing for Addison’s disease
- Serum fructosamine to confirm diabetes mellitus (performed in cats more often 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
- Tests for heart disease, including heartworm test, chest X-rays, ProBNP blood test, electrocardiogram, and echocardiogram if abnormalities in heart size, rate, rhythm, or sounds are identified
- Testing for specific infectious diseases (may be regional)
