VETzInsight

Laboratory Tests Hinting at Cushing's Syndrome

January 1, 2001 (published) | October 9, 2019 (revised)

When an animal sees the veterinarian for a potential clinical problem, an initial database is collected in the form of a blood panel and urinalysis, and possibly a urine culture. There are some tip offs to Cushing's syndrome that may be noted and added to the list of observed symptoms as evidence.

The Stress Leukogram

This term refers to the relative proportions of different types of white blood cells. There is a typical pattern produced by cortisol as the body responds to stress. This pattern is called a stress leukogram. If this pattern is seen in a patient that does not seem stressed, there is a possibility that an excess of cortisol is present.

The stress leukogram classically involves:

  • Elevated neutrophil count
  • Lowered lymphocyte count
  • Lowered eosinophil count

These are all types of white blood cells counted in a test called a complete blood count (or CBC for short). You don't need to know what those cells do; it is the pattern of increases and decreases that suggests cortisol is afoot.

Photo by CDC Public Health Image Library

Elevated Alkaline Phosphatase

Alkaline phosphatase (often abbreviated ALP or SAP) is one of the so-called liver enzymes, meaning that it is chiefly found in the liver. There is a form of this enzyme that is produced in high levels in response to cortisol. This enzyme is not harmful in excess levels but since such marked increases in its levels are associated with cortisol, this would be a good hint that either this patient is taking cortisone-type medications or has Cushing's disease.

Elevated Cholesterol

This is a common finding in most endocrine diseases and, in this case, results from abnormal fat mobilization. High levels of circulating cholesterol may, as in humans, alter normal circulation and blood clotting.    

These classic laboratory findings complement the physical examination and may lead your veterinarian to recommend definitive testing for Cushing's syndrome. Not all of these findings need be present to suggest further testing for Cushing's Syndrome but the suggestion is stronger as more of these hints are detected.

Unconcentrated Urine and/or Bladder Infection

Photo by MarVistaVet

When a pet drinks excessive amounts of water, the extra water is passed as urine. As long as there is extra water, urine will be dilute. Because of the immunosuppression associated with Cushing's disease, there may be evidence of bacterial infection as well, or such evidence may be concealed by the dilution of the urine. Ideally urine should be cultured if it is too dilute to reliably detect white blood cells or blood. Recent studies have shown that 20 percent of dogs with Cushing's disease have an inapparent bladder infection.

Feline Cushing's Disease is a Little Bit Different

The classical screening test findings seen in dogs are not typically seen in cats. Most cats with Cushing's disease do not have a stress leukogram as described above. They do not have elevations in cholesterol or liver enzymes and their thyroid levels tend to run in the normal range. Most cats with Cushing's disease are diabetic and have findings referable to that. Classically the cat with Cushing's disease has especially intractable diabetes mellitus and diabetic control seems to require high insulin doses if it can be controlled at all. It is generally the diabetes mellitus that is diagnosed first in a cat with Cushing's disease. If the diabetes does not respond to insulin as expected, underlying causes are sought and one of these is Cushing's disease. For more information on other possibilities, read about hard to regulate diabetic cats.


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