A lack of appetite (inappetance) and energy (lethargy) are clinical signs associated with many different diseases and conditions, but these symptoms are not specific for any particular disease.
It is important to try to determine from the history that you provide, and from a thorough physical examination of your pet, if there is a non-medical cause of these clinical signs, if these signs are related to physical difficulties in eating or if an underlying systemic illness is at the root of these signs.
Non- medical causes of decreased appetite and lethargy include dietary changes, changes in the usual routine at home (walking schedule, feeding schedule), and stresses such as new additions to the family (human or animal).
Your pet may be having difficulty grasping, chewing, or swallowing food because of infections in the oral cavity or esophagus,
Severe periodontal disease can cause
general malaise. dental problems, or rarely because of neuromuscular (nerves and/or muscle innervation) diseases.
The list of systemic diseases that may include inappetance and lethargy as clinical signs is extensive. A partial listing of these diseases include: heart disease, kidney disease, liver disease, hypothyroidism, hypoadrenocorticism (Addison’s disease), immune-mediated diseases, neoplasia (cancer), respiratory disease, gastrointestinal diseases, and infections.
Pain, certain drugs and the ingestion of toxins may also result in a decreased appetite and lethargy.
A physical examination of your pet along with a detailed history should rule out environmental changes and physical problems with eating as causes of his inappetance and lethargy.
A panel of screening tests is recommended, especially if there is no obvious cause for your pet’s clinical signs.
The screening tests include a complete blood count (CBC), a serum biochemical profile, and a urinalysis. A serum thyroxine (Total T4) concentration is also suggested in middle aged to older animals.

The CBC (complete blood count) requires a single blood sample and provides an evaluation of the red blood cells, the white blood cells, and the platelet components of that sample. The total numbers of these cells are evaluated along with specific cellular characteristics.
The presence of anemia, denoted by a decrease in the red blood cell numbers, packed cell volume and hemoglobin of a blood sample, may be noted. Often the degree of anemia is mild and typically resolves once the underlying condition or disease has been addressed. However, occasionally the degree of anemia may be severe, and may suggest an immunemediated cause of red blood cell destruction.
The presence of underlying inflammatory or infectious diseases will usually be indicated by increases in the white blood cell numbers.
From: Laboratory Urinalysis and Hematology by Carolyn Sink
Published by Teton NewMedia
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2004 with permission
Leukemia, although relatively rare, may result in inappetance and lethargy. Leukemia is diagnosed on the CBC by large increases in certain white blood cell types or by the appearance of unusual white blood cells on the blood smear.
The serum biochemistry profile requires a separate blood sample, from which the serum (the liquid portion of blood) is separated from the cellular portion. Serum contains many substances including glucose, lipids (fats), proteins, and metabolic waste products.
The use of a serum biochemistry profile allows us to measure these components of serum and also provides us with specific values for enzymes related to the liver, kidneys, and pancreas, in addition to an evaluation of the electrolyte components of a serum sample.
Changes or patterns of change within the serum biochemistry profile may indicate that a specific disease is responsible for your pet’s clinical signs, whereas biochemistry results within the normal or reference range may make the presence of certain diseases highly unlikely.
For example, increases in BUN (blood urea nitrogen) and creatinine, suggest underlying kidney disease. Similarly, a marked increase in the pancreatic enzymes amylase and lipase is supportive of pancreatitis (pancreatic inflammation).Occasionally decreased biochemical values may suggest a specific underlying disease. For example, decreases in serum glucose, albumin and BUN may be associated with liver failure.
The consequences of inappetance may be reflected on the biochemistry profile. When overweight cats stop eating, their livers can become overwhelmed by fat that is released

from tissue stores (a condition called hepatic lipidosis or fatty liver syndrome). This condition may be reflected by increases in specific liver enzymes.
A urinalysis is essential for the proper interpretation of changes that may be found on the serum biochemistry profile. These two screening tests should always accompany one another, and be performed at the same time.
If for example the serum BUN and creatinine values are increased and the urinalysis indicates that the urine is very dilute, then these findings support kidney disease.
Conversely the findings of increased serum BUN and creatinine with a concentrated urine sample supports dehydration
A urine dipstick tests the properties of urine.
A urinalysis allows us to detect the presence of red blood cells, white blood cells, glucose, and protein within the urine sample. Therefore the presence of infections or inflammation of the urinary tract, diabetes, and excessive urinary protein loss may either be diagnosed or ruled out.
The kidneys constantly filter blood to remove toxins and other wastes and concentrate the extracted materials into urine. Therefore increases in the blood concentrations of substances such as bilirubin (a pigment associated with liver disease), may be detected by urinalysis before increases are noted with blood testing.
A serum thyroxine (total T4) test may be indicated in dogs to rule out hypothyroidism
(decreased thyroid function) as a cause of lethargy and inappetance. Hypothyroidism is indicated by a serum thyroxine concentration below the reference range.
That depends upon the results of the screening tests.
It is impossible to predict what changes or conditions that may be uncovered with the screening tests. However, in most instances this screening panel will provide either a specific diagnosis or a direction for further investigation.
If, for example, the screening tests are suggestive of hypoadrenocorticism (Addison’s disease), then we will need to confirm the presence of this condition by further testing, specifically with an ACTH stimulation test. (See handouts on Addison’s disease and
ACTH testing for further information).
If decreased liver function is suspected, then further evaluation of liver function may be recommended, including serum bile acid test or perhaps radiographs or ultrasound imaging. ( See handout on liver disease for more information).

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This client information sheet is based on material written by Kristiina Ruotsalo, DVM, DVSc, Dip ACVP &
Margo S. Tant BSc, DVM, DVSc.
© Copyright 2004 Lifelearn Inc. Used with permission under license. April 10, 2020