10 simple but essential tests

The demand for high-quality veterinary care has steadily increased over the last three decades, leading to major advances in veterinary medicine. Many of the same diagnostic tools used in human medicine are now readily available to general veterinary practitioners. Owners are aware of these tools as well and often assume that referral to specialists for these diagnostic tests is what stands between their pets and an accurate diagnosis.

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.

1 Blood pressure measurement

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.

4 Urine cortisol: creatinine ratio

This simple diagnostic test is a great screening test for hyperadrenocorticism, one of the most common endocrine diseases in dogs. A single urine sample, usually collected at home by the owners, is submitted, and the ratio of cortisol to creatinine is determined. This test has a high sensitivity (few false negative results), and a result within the reference range virtually assures you that the patient does not have hyperadrenocorticism.

However, the urine cortisol:creatinine ratio has low specificity (many false positive results) and is not useful for diagnosing Cushing's disease. A result above the reference range may be due to hyperadrenocorticism, excitement, concurrent illness, or normal circadian variation in cortisol concentrations.

5 Urinalysis

An often-overlooked component of the minimum database, a urinalysis should be submitted at the same time a complete blood count (CBC) or serum chemistry profile is performed. The urine specific gravity, one of the most important parameters measured on a urinalysis, is essential for localizing azotemia (prerenal, renal, postrenal). Additionally, low urine specific gravity is seen with many serious diseases including renal failure, liver disease, and both hyperadrenocorticism and hypoadrenocorticism.

Bilirubinuria may be an early indicator of liver disease, and a urine sediment examination may help with diagnosing renal disease, assessing the risk of urolith formation, or identifying animals with asymptomatic urinary tract infections.

When proteinuria is noted on the urinalysis in the absence of an active urine sediment or signs of lower urinary tract disease, a urine protein:creatinine ratio is indicated. Since proper management of protein-losing nephropathies may increase survival time, proteinuria warrants treatment and serial monitoring.6,7 Proteinuria in patients with renal failure worsens prognosis; however, appropriate treatment may improve both a patient's quality of life and survival time.

6 Bacterial culture and antimicrobial sensitivity testing

Many patients presented to their veterinarians for evaluation of various clinical signs are empirically treated with an antibiotic, which—without a doubt—can be effective. However, in many animals, the clinical signs return, and it becomes unclear whether infection has recurred or was inadequately treated or whether the initial antibiotic course simply had a placebo effect. Additionally, the prevalence of multidrug-resistant infections such as methicillin-resistant Staphylococcus aureus has been increasing, so responsible antibiotic therapy is essential.

Consequently, all patients—even those with their first urinary tract infection, first bout of otitis, or initial bout of coughing—should undergo bacterial culture and antimicrobial sensitivity testing before receiving antibiotics whenever possible, even though this adds expense for clients.8 Obtaining a sample of urine, purulent material, or tracheal wash fluid is generally a simple procedure and can be essential in directing appropriate antibiotic choice.

7 Coagulation time

Testing coagulation time is much easier now with point-of-care machines. Knowing a patient's coagulation status is particularly useful in diagnosing possible rodenticide toxicosis, liver failure, or disseminated intravascular coagulation. Assessing coagulation time allows you to prioritize differential diagnoses and diagnostic tests and to help determine prognosis and treatment options. Coagulation testing also preemptively establishes the risks associated with more invasive diagnostic tests. Identifying abnormalities in coagulation times allows the problem to be addressed before serious consequences such as hemorrhage, shock, or death occur.

8 At-home glucometer use

Glucometers can now be routinely used for at-home monitoring of diabetic patients. At-home testing is advantageous because stress-induced increases in blood glucose concentrations are especially a concern in hospitalized cats and may confound the results of in-hospital glucose curves. Such results may prompt inappropriate increases in insulin dose, potentially resulting in hypoglycemic crises or the Somogyi effect. Most owners are able to easily perform blood glucose curves at home, and the results are as effective for managing diabetic patients as glucose curves performed in the hospital.9

9 Preanesthetic testing

Preanesthetic testing (CBC, serum chemistry profile, urinalysis) is unfortunately often overlooked or declined, particularly in geriatric but overtly healthy patients presenting for elective procedures such as dental prophylaxis. These patients may have occult diseases, and a diagnosis before anesthesia will minimize the occurrence of unforeseen complications. Additionally, preanesthetic testing is an opportunity to detect disease processes early when they may be more treatable. Finally, liver or kidney disease will affect anesthetic protocols, the intensity of intraprocedural monitoring, and intravenous fluid type and rate.

10 Neurologic examination

Performing a complete neurologic examination is often overlooked in patients presenting with possible neurologic abnormalities. As with a standard physical examination, a good neurologic examination requires practice and comfort with knowing what is normal. Localizing a neurologic lesion is required for formulating a differential diagnosis list and dictates the appropriate diagnostic test and treatment plan. For example, in a patient with cranial nerve abnormalities, prognosis and treatment strategies for forebrain disease, cervical disease, Horner's syndrome, or peripheral vestibular disease are all vastly different. Only proper lesion localization will allow you to discuss the next best steps with owners. Even when a referral is sought, the initial presenting neurologic examination results are extremely useful for documenting the progression of clinical signs, as neurologic status can change quickly and the rapidity of change may alter a patient's prognosis and management strategy.

Final thought

Some of these 10 essential tests have simply been underused in veterinary practice, and others are newly available. Improve the quality of your patient care and increase your success rate for obtaining diagnoses and appropriately treating patients by adding these tests to your armamentarium.

Editors' note: Dr. Pressler is a paid consultant for IDEXX and has received funding from HESKA.

Barrak Pressler, DVM, DACVIM, and Alice A. Huang, VMD, Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907.

REFERENCES

1. Silverstein DC, Wininger FA, Shofer FS, et al. Relationship between Doppler blood pressure and survival or response to treatment in critically ill cats: 83 cases (2003-2004). J Am Vet Med Assoc 2008;232(6):893-897.

2. Brady CA, Otto CM, Van Winkle TJ, et al. Severe sepsis in cats: 29 cases (1986-1998). J Am Vet Med Assoc 2000;217(4):531-535.

3. Fantoni DT, Auler Junior JO, Futema F, et al. Intravenous administration of hypertonic sodium chloride solution with dextran or isotonic sodium chloride solution for treatment of septic shock secondary to pyometra in dogs. J Am Vet Med Assoc 1999;215(9):1283-1287.

4. Adler JA, Drobatz KJ, Hess RS. Abnormalities of serum electrolyte concentrations in dogs with hypoadrenocorticism. J Vet Intern Med 2007;21(6):1168-1173.

5. Thompson AL, Scott-Moncrieff JC, Anderson JD. Comparison of classic hypoadrenocorticism with glucocorticoid-deficient hypoadrenocorticism in dogs: 46 cases (1985-2005). J Am Vet Med Assoc 2007;230(8):1190-1194.

6. Jacob F, Polzin DJ, Osborne CA, et al. Evaluation of the association between initial proteinuria and morbidity rate or death in dogs with naturally occurring chronic renal failure. J Am Vet Med Assoc 2005;226(3):393-400.

7. Lees GE, Brown SA, Elliott J, et al. Assessment and management of proteinuria in dog and cats: 2004 ACVIM Forum Consensus Statement (small animal). J Vet Intern Med 2005;19(3):377-385.

8. Morley PS, Apley MD, Besser TE, et al. Antimicrobial drug use in veterinary medicine. J Vet Intern Med 2005;19(4):617-629.

9. Reusch CE, Kley S, Casella M. Home monitoring of the diabetic cat. J Feline Med Surg 2006;8(2):119-127.