Barrak Pressler, DVM, DACVIM, and Alice A. Huang, VMD

However, many great diagnostic tests are relatively inexpensive and can be performed in virtually any practice. So with the help of Veterinary Medicine's Editorial Advisory Board and Practitioner Advisory Board, we have come up with 10 simple tests that are frequently overlooked. These tests provide valuable information in sick dogs and cats and are vital to the practice of high-quality medicine.

Occasionally, we find ourselves saying, "If only the referring veterinarian had performed a ____________ test." These are the 10 diagnostic tests that most commonly fill in that blank.

Maintaining normal blood pressure is critical for any patient, as marked hypotension or hypertension can rapidly lead to permanent organ dysfunction and death. Hypertension-related end-organ damage most commonly affects the central nervous system, heart, kidneys, and eyes; the kidneys in particular are prone to damage with marked hypotension. Patients with blood pressure abnormalities do not always present in lateral recumbency or in a coma. Often the signs associated with hypotension or hypertension are subtle, such as lethargy or anorexia. Fortunately, blood pressure measurement is inexpensive and easy to perform, and the instruments are readily available.

Blood pressure measurement should be performed in dogs and cats with clinical signs or clinicopathologic changes referable to the above organ systems—acute blindness, renal failure, and seizures, for example—and in animals with systemic diseases such as sepsis that may be associated with hypotension.^1-3 This modality should also be a routine part of anesthetic monitoring in patients.

2 Serum electrolyte measurement

Always include serum electrolyte measurement in any serum chemistry profile. Severe electrolyte disturbances can lead to life-threatening abnormalities such as arrhythmias or seizures. Electrolyte concentrations are also critical for choosing appropriate fluid therapy and for working up patients with polyuria and polydipsia. Many of the diseases that serum chemistry profiles screen for may cause abnormalities in electrolytes as well, such as renal disease, urinary tract obstruction or rupture, gastrointestinal tract obstruction, and diabetic ketoacidosis.

Hypoadrenocorticism (Addison's disease) is one of the most common diseases that may be missed by not checking electrolyte concentrations. A change in the sodium or potassium concentration is often the first abnormality to increase clinical suspicion of this disease. A sodium:potassium ratio < 24 is highly suggestive of hypoadrenocorticism.⁴

3 ACTH stimulation testing

Patients that present with stereotypical signs of hypoadrenocorticism or hyperadrenocorticism are clear candidates for ACTH stimulation testing; however, this test should not be overlooked in dogs and cats with less classic signs.

In dogs with Addison's disease, lethargy may be the only presenting complaint, and a mild increase in serum potassium concentration or an unexpected lack of a stress leukogram may be the only abnormal laboratory test result. A recent review of patients with atypical hypoadrenocorticism at Purdue University suggests this disease is more common than previously thought.⁵ The clinical signs and laboratory data of an Addisonian patient often mimic those of patients with mild or severe gastrointestinal, renal, or liver disease. Fortunately, the ACTH stimulation test is highly sensitive and specific for hypoadrenocorticism and, thus, should be performed in patients with potentially consistent signs.

The ACTH stimulation test can also be used to screen for hyperadrenocorticism. It requires less time and effort than a low-dose dexamethasone suppression test and is less prone to false positive results than other screening tests. Generally, an ACTH stimulation test should be performed in patients presenting with polyuria and polydipsia without an obvious cause based on the initial minimum database screening test results. In addition, dogs with hyperadrenocorticism may also present with subtle manifestations of disease, such as mild bilateral alopecia or polyuria and polydipsia without the classic potbellied appearance or polyphagia.