Testing for Decreased Appetite with Listlessness

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

My pet isn’t eating well and seems listless. What might be the problem?

Decreased appetite (inappetence) and listlessness (lethargy or lack of energy) are seen with many different diseases and conditions. The first step is to determine if the underlying problem is medical or non-medical in nature.

Non-medical causes of inappetence and listlessness are often associated with stress or anxiety. Pets in highly stressful situations may lose interest in food and become withdrawn and appear listless. Events such as moving to a new home, the addition of a new baby or new pet to the household, the absence of a favorite family member, or the loss of a housemate are common non-medical causes of inappetence and lethargy.

Medical causes are far more common, and most pets showing decreased appetite and listlessness have an underlying medical condition. Sometimes the problem is limited to the mouth or esophagus, and pets with these disorders have difficulty grasping, chewing, or swallowing food. Common causes include severe periodontal disease, infections or tumors of the mouth or esophagus, injury to the jaw or tongue, and occasionally nerve damage.

“Medical causes are far more common, and most pets showing decreased appetite and listlessness have an underlying medical condition.”

However, in most cases the pet is suffering from systemic disease, which is an illness that involves the whole body. There are many systemic diseases that cause decreased appetite and listlessness. A few common ones include heart disease, kidney disease, liver disease, hypothyroidism (underactive thyroid gland), hypoadrenocorticism (a failure of the adrenal gland, also called Addison's disease), immune-mediated diseases, respiratory disease, gastrointestinal diseases, infectious disease, and cancer.

In addition, pain, certain medications, and some types of toxins may also cause decreased appetite and lethargy.

This list is huge! How can you possibly find out what’s bothering my pet?

The search for answers starts with a complete history and physical examination. A pet’s history is the information you give your veterinarian about your pet’s illness. In a pet showing poor appetite and listlessness, this would include details about how long the pet has been ill and whether there have been changes in drinking, urination, and bowel habits. It would be helpful to know if there were any other signs of illness such as coughing, vomiting, or changes in weight. History often helps to narrow down the list of possible diagnoses. For example, an older cat that is losing weight and drinking excessively might have kidney disease, while a middle aged dog that is gaining weight and seems fine otherwise may have an underactive thyroid gland.

A thorough physical examination involves looking at all parts of the body, and typically includes listening to the heart and lungs with a stethoscope and palpating the abdomen (gently squeezing or prodding the abdomen with the fingertips to detect abnormalities of the internal organs). Physical examination can sometimes uncover the cause of a pet’s poor appetite and listlessness. For example, the presence of an abnormal heartbeat may indicate heart failure; a mass in the abdomen could be a sign of cancer; very pale gums indicates anemia.

Although history and physical examination are important first steps, your veterinarian may recommend doing screening tests. These are simple tests that provide valuable information about the overall health of your pet and often provide clues about the underlying problem.


What screening tests are recommended?

The most common screening tests include complete blood count, serum biochemistry profile, and urinalysis.

What can these screening tests tell us?

A) The Complete Blood Count (CBC) provides information about the three different cell types in the blood. These are: 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. See handout "Complete Blood Count" for further information.

In a pet with decreased appetite and listlessness, some changes that might be seen on the CBC include:

  • anemia (low hemoglobin levels; not enough red blood cells). This could indicate a bleeding disorder, immune mediated disease, nutritional problems, or longstanding systemic disease which is affecting many different body systems at the same time.
  • abnormal numbers of white blood cells. Increases or occasionally decreases in the numbers of white blood cells could indicate underlying inflammation or infection.
  • signs of bone marrow disease. Very high or very low numbers of blood cells together with the presence of abnormal cells in the blood could signal bone marrow disease including leukemia (bone marrow cancer).

B) Serum biochemistry refers to the chemical analysis of serum, which is the pale yellow liquid part of blood that remains after the cells and clotting factors have been removed. Serum contains many substances including enzymes, proteins, lipids (fats), glucose (sugar), hormones, electrolytes, and metabolic waste products. Testing for these substances provides information about the health of various organs and tissues in the body, as well as the metabolic state of the animal. Changes and abnormalities in the biochemistry profile can indicate the presence of specific diseases and can provide clues about other problems. See handout “Serum Biochemistry” for further information.

In a pet that is not eating and seems listless, the serum biochemistry may show changes such as:

  • increased levels of urea and creatinine, suggesting underlying kidney disease.
  • an elevated glucose level (blood sugar), usually a sign of diabetes mellitus (sugar diabetes), especially in a dog.
  • decreased levels of glucose, albumin and urea, possibly indicating liver failure.
  • increased levels of liver enzymes, suggesting liver damage.

C) Urinalysis is a simple test that analyses the physical and chemical composition 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 for the proper interpretation of the serum biochemistry profile and should be done at the same time as blood testing. See handout “Urinalysis” for further information.

In a pet that is listless and not eating well, the urinalysis may show signs of:

  • kidney disease.
  • bladder infection.
  • cancer of the kidneys, bladder, or reproductive system.

 Will further testing be required?

Screening tests may provide a diagnosis but further testing will likely be recommended. Depending on the results of a pet’s history, physical examination, and screening tests, some of these additional tests could include:

  • serum thyroxine (total T4) test in dogs suspected of having hypothyroidism (low thyroid function).
  • pancreatic specific lipase immunoreactivity (PLI) if pancreatitis is suspected, especially in cats.
  • ACTH stimulation test if the screening tests suggest hypoadrenocorticism (Addison's disease). See handouts “Addison’s Disease in Dogs”, “Addison’s Disease in Cats” and “Serum ACTH” for further information.
  • liver function tests such as pre- and post-prandial serum bile acid test if liver damage is suspected. See handout “Bile Acid Test” for further information.

Additional testing may involve:

  • radiographs (X-rays) or ultrasound to evaluate the heart lungs, liver, kidneys, pancreas, or bowel, and to look for cancer.
  • bacterial culture and sensitivity to detect bacterial infections.
  • tests for specific infectious diseases such as feline leukemia virus or feline immunodeficiency virus in cats, or Lyme disease in dogs.
  • tests for immune mediated disease.
  • tests for anemia such as fecal occult blood, blood iron studies, bone marrow evaluation.
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