Testing for Diarrhea
What are the causes of diarrhea?
Many different diseases and conditions may result in diarrhea. The frequency, urgency, and physical characteristics of the diarrhea, along with a history and other clinical signs that your pet is exhibiting may provide some clues to its cause. For example, a puppy with diarrhea containing white 'spaghetti-like' strands is likely experiencing diarrhea associated with intestinal parasitism (worms). Unfortunately, in most instances, the underlying cause of diarrhea is not that obvious.
Although by no means a complete list, the following outlines some of the most common causes of diarrhea:
- Conditions related to the gastrointestinal tract including inflammation, bacterial or viral infections, parasites, tumors, dietary changes, dietary indiscretion, and maldigestion or malabsorption of food.
- Systemic and endocrine (hormonal) diseases such as liver disease, kidney disease, pancreatic disease, hyperthyroidism and hypoadrenocorticism can result in bouts of diarrhea.
- Certain drugs and toxins may be associated with diarrhea.
This list is huge! How can we possibly determine the cause in my pet?
Certain diseases are more common in certain species (dogs versus cats) or breeds, and within certain age groups (puppies and kittens versus adult animals), which may narrow down the range of possibilities. In addition, the specific history, which includes any medications or supplements that your pet have recently received, when combined with the results of a thorough physical examination, will often narrow the list of possibilities further.
A selected panel of screening tests will allow further shortening of the list, and may sometimes provide a definitive diagnosis.
What screening tests are recommended?
The screening tests include a complete blood count (CBC), a serum biochemistry profile, a urinalysis, and a fecal flotation. In middle aged to older cats, a serum thyroxine (total T4) concentration is also recommended.
Do all of these tests need to be performed if my pet is feeling well other than the occasional bout of diarrhea?
No. If your pet is otherwise bright and alert and if the physical examination reveals no significant findings, then all of these tests are probably not necessary for an initial, mild bout of diarrhea. This is especially true if there is a reasonable explanation for the condition - for example, a puppy or kitten with intestinal parasites (worms) or with a recent change in diet may experience diarrhea. In this instance, a fecal flotation and appropriate antiparasitic treatment, or a more gradual diet change, would suffice.
If the episodes of diarrhea occur more frequently, if your pet does not respond to conservative therapy (a bland diet for example), or if your pet shows clinical signs of being unwell (fever, depression, a sore abdomen), then these screening tests are strongly recommended.
What can these tests indicate?
In addition to providing information regarding the possible cause of your pet's symptoms, these screening tests may uncover secondary effects of chronic diarrhea such as electrolyte disturbances. In older animals, previously undetected underlying conditions that warrant medical attention may also be discovered.
"...screening tests may uncover secondary effects of chronic diarrhea such as electrolyte disturbances."
The CBC (complete blood count) requires a single blood sample and provides us with 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.
Because diarrhea involves fluid loss, the CBC can tell us if your pet has become dehydrated. Dehydration is indicated by an increase in the packed cell volume (PCV) and total red blood cell numbers of the sample.
Blood loss related to the diarrhea may be noted on the CBC. Blood may be lost because of underlying intestinal inflammation, ulceration or tumors. Such blood loss is indicated by decreases in the total red blood cell numbers and PCV of the sample. Depending on the site of blood loss, and its duration, features of iron deficiency anemia may be noted.
An elevated white blood cell count may suggest underlying inflammation or infection as a cause of the diarrhea. Some conditions may be accompanied by increases in specific white blood cell types; an increase in eosinophils may be noted with parasitism and food allergies, for example. Some viral infections are initially accompanied by severe decreases in the numbers of white blood cells. Such changes are important to document, because not only do they help pinpoint a possible cause of your pet's symptoms, but also because they indicate whether specific treatments such as antibiotics are required.
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, electrolytes, enzymes, and metabolic waste products. A biochemistry profile allows us to measure all of these components of serum and provides us with specific values for enzymes directly related to the liver, kidneys and pancreas.
Changes and patterns of change within the serum biochemistry profile may show 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.
Examples of changes suggesting specific diseases include increases in the liver enzymes ALT (alanine transaminase) and AST (aspartate transaminase) indicating underlying liver damage. Similarly, increases in the pancreatic enzymes lipase and amylase are supportive of underlying pancreatitis.
Changes in the electrolyte composition of serum are important because not only may they suggest certain diseases such as hypoadrenocorticism (Addison's disease), but also they document any electrolyte imbalances that are a direct result of the diarrhea.
"A urinalysis is essential for the accurate interpretation of changes noted on the serum biochemistry profile."
A urinalysis is essential for the accurate interpretation of changes noted on the serum biochemistry profile. These two screening tests should be taken simultaneously.
If, for example, the serum protein values are decreased, and the urinalysis indicates that the urine sample contains very little protein, then chronic diarrhea may be causing excessive protein loss from the body through the gastrointestinal tract.
Since the kidneys constantly filter the blood to remove waste products, and concentrate the extracted materials into urine, changes in substances such as bilirubin (a pigment that is associated with liver disease) may be seen on a urinalysis before they are detected on a blood sample. The presence of specific crystals in urine such as bilirubin crystals or ammonium biurate crystals may also point to underlying liver disease as a cause of chronic diarrhea.
A fecal flotation simply requires that a fresh fecal sample be microscopically evaluated for the presence of parasite eggs. Intestinal parasitism is common in puppies and kittens, but any age of animal can be affected.
A serum thyroxine (total T4) test is recommended in older cats. This test does not require further blood to be obtained from your cat; the sample taken for the biochemistry profile will suffice. The total amount of thyroid hormone in the sample is determined. A normal result will help to eliminate hyperthyroidism as a cause of your cat's diarrhea, whereas increased values are supportive of hyperthyroidism.
Will further testing be required?
That depends upon the results of the screening tests.
"It is impossible to predict what changes or conditions that may be uncovered with the initial screening tests."
It is impossible to predict what changes or conditions that may be uncovered with the initial screening tests. However, in most instances, this screening panel will provide either a specific diagnosis or a logical direction for further investigation.
If the screening tests are suggestive of a viral or bacterial infection as a cause of the diarrhea, then further investigations may involve submission of a fecal sample for viral antigen testing or bacterial culture.
Occasionally no specific changes are found on the screening tests, especially if gastrointestinal disease is suspected based on the clinical signs that your pet is exhibiting. This is often the case with dogs suspected to be suffering from exocrine pancreatic insufficiency. Exocrine pancreatic insufficiency (EPI) is a disease of the portion of the pancreas that is involved in the production of digestive enzymes. EPI can be diagnosed with a single fasted blood sample using a test to detect trypsin-like immunoreactivity (TLI).
In some instances laboratory testing will not provide us with the answer and we may need to evaluate the intestinal tract via other diagnostic procedures such as radiography (possibly including a specialized barium series), ultrasound, endoscopy or exploratory surgery. Tissue biopsy samples for diagnostic interpretation may be taken during some of these investigations.