November 2006 Issue

Featured case study:
Six-year-old neutered domestic shorthair cat with a history of lethargy, weight loss and anorexia
by Dr. Annette Cowell of the Cat Clinic of Stillwater, Stillwater, Oklahoma

Differential diagnosis
Because of a lack of clear direction based upon clinical signs and physical examination findings, a short differential for lethargy, weight loss and anorexia was not possible. A variety of metabolic, inflammatory and neoplastic processes that could be systemic in character were considered.

Plan
Zeke’s initial workup included treating for fleas with Imidocioprid and collecting blood for a complete blood count (CBC) and general chemistry profile as well as collecting urine for a urinalysis. Results from these tests would hopefully provide further insight into the underlying disease process.

Laboratory data

Erythron—The red blood cell indices suggest a microcytic and slightly hypochromic population of cells supportive of chronic blood loss. This could easily be explained because of the fleas noted at physical examination. No major red blood cell morphologic changes are noted; however, with critical review of the blood film, there is slight increase in the amount of central pallor compared to normal feline erythrocytes and this is additional support for the red blood cell indices changes from the reference interval limits. The high RBC count is most likely associated with the degree of dehydration documented at physical examination as well as the average decreased size of the red blood cells.

Leukon—The leukogram is characterized as a mild leukocytosis with a mild-to-moderate absolute neutrophilia, lymphopenia and moderate monocytosis. These changes are most consistent with an inflammatory process (monocytosis and neutrophilia) and superimposed glucocorticoid influence (lymphopenia and neutrophilia). Examination of the peripheral blood film shows evidence of a mild-to-moderate left shift (see Figure 1), which definitively indicates that there is an active inflammatory process along with a glucocorticoid influence. Only rarely seen lymphocytes are noted on scanning the blood film, and reactive lymphocytes are noted.

Thrombon—Platelets numbers are mildly increased and enlarged platelet forms are seen; however, the finding of enlarged platelet forms in the peripheral blood of a cat is often equivocal.

Glucose—There is a moderate hyperglycemia, and in light of the fact that Zeke was not excited during the physical examination or during blood collection, transient physiologic hyperglycemia associated with an epinephrine or glucocorticoid influence is highly unlikely. In addition, there is both glucosuria and ketonuria present, which support persistent hyperglycemia and ketoacidosis, respectively. Diabetic-associated ketoacidosis is indicated.

Acid-base—Sodium and potassium are within reference interval limits, chloride and TCO₂ (bicarbonate) are decreased and there is an increased anion gap. The decreased TCO₂ and increased anion gap indicate the presence of a titrational metabolic acidosis with an increase in the amount of unmeasured anions. In this case, the ketonuria supports the presence of ketone bodies in circulation, which are an unmeasured anion. The relative low chloride compared to sodium is supportive of either chloride sequestration or loss; the potential of both, including occult gastric vomiting, must be considered and a complicating metabolic alkalosis is likely present. Figure 2 attempts to visually describe Zeke’s electrolyte disturbance at presentation.

Liver-panel—There is a mild-to-moderate increase in ALT, which indicates the presence of mild-to-moderate hepatocellular injury. This may merely represent secondary changes associated with the diabetic ketoacidosis condition. The ALT findings are not specific; however, based upon the diagnosis of diabetes, vacuolar hepatopathy and possible hepatic lipidosis should be considered. The finding of increased bilirubin as well as the slightly increased ALKP, minimal increase in GGT and increased cholesterol support cholestatic disease, which could also be a secondary effect associated with a diabetes-induced vacuolar hepatopathy. The finding of a marked bilirubinuria supports the hyperbilirubinemia reported and the presence of cholestasis.

Urinalysis—Beyond the few comments above related to glucosuria, ketonuria and bilirubinuria, there are no significant urinalysis abnormalities.

Protein profile—There is a slight hyperproteinemia characterized primarily by a slight hyperglobulinemia. Changes are likely associated with the dehydration or inflammation present or a combination of the two processes.

Final diagnosis
Diabetic ketoacidosis with secondary hepatopathy

Therapeutic plan and progress
Fluids and insulin were administered and a series of serum glucose measurements were made in attempts to regulate Zeke’s ketoacidotic diabetic condition. Correcting the electrolyte imbalances and acid base disorder was considered as important as insulin therapy. Serum phosphorus concentration often decreases and hypokalemia becomes evident with treatment. With insulin therapy, potassium moves into the cells with glucose; therefore, potassium must be closely monitored during the regulation process. Potassium administration may need adjustments during the process.

Day 1

Day 2

Day 3

On day three potassium normalized, but there was still concern about hepatic lipidosis because Zeke was still not eating.

Day 4

Zeke began eating on his own on Day 4.

Day 5
The intravenous catheter was removed and Zeke was sent home with 1 unit of Humulin L (100 units/ml) twice daily.

Day 12
The owner reported that Zeke was returning to his old self. There was a slight increase in his weight, which was now 11 lb. 4 oz. One unit of Humulin L was continued twice daily.

Day 12

Case Outcome
Several glucose curves were performed on Zeke over the next year and control was not adequate. The dosage of Humulin L was gradually increased to a high of 5 units twice daily over the next year. Clinical signs of polyuria and polydypsia were still present almost one year after presentation. Zeke was changed to 2 units PZI (Protamine Zinc Insulin) (40 units/mL) twice daily and he was placed on a DM (high protein and low carbohydrate) diet. The lower units/mL made it easier for the owner to correctly medicate Zeke.

Zeke continued to do well on PZI and is currently taking 3 units twice daily. He has a problem with his weight (currently weighs 18 lb.) and likely has some degree of insulin resistance related to that issue. His family and Zeke seem happy with his current condition.

Note: A story about Zeke can be found on the clinic Web site (www.catclinicofstillwater.com) under the Amazing Patients section.

The recommendations contained in Diagnostic Edge educational materials are intended to provide general guidance only. As with any diagnosis or treatment, you should use clinical discretion with each patient based on a complete evaluation of the patient, including history, physical presentation and complete laboratory data. With respect to any drug therapy or monitoring program, you should refer to product inserts for a complete description of dosages, indications, interactions and cautions.

Do you have a case that you would like to submit? E-mail us at diagnosticedge@idexx.com to get the process started.

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Give your analyzers breathing room

Each of the IDEXX VetLab® analyzers requires ample ventilation. This ensures that the heat generated by the electronics and motors inside the instrument can dissipate, helping to keep the analyzer’s internal temperature within the appropriate operating range.

The specific environmental requirements for each instrument can be found in that instrument's operator’s manual, but some general guidelines are:

1. Position the analyzers so the exhaust fans do not blow air directly onto another analyzer and do not blow the air into an area that could trap it near the instrument.

2. Do not set up the analyzer in direct sunlight or near another source of heat, such as a radiator or heat duct.

3. Clean the fan filters routinely to ensure they do not get clogged with dust or pet hair.

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The LaserCyte® Hematology Analyzer shows excellent correlation

A recent research summary, Evaluation of a Point-of-Care Hematology Analyzer in Dogs and Cats Receiving Anticancer Chemotherapy (A Lara, O’Keefe AC, et al.), concluded that the LaserCyte® Analyzer showed excellent correlation with results obtained by standard methods in dogs and cats undergoing chemotherapy.¹

Results compared included HCT, PLT, WBC and neutrophil counts. The LaserCyte analyzer also accurately detected anemia, leucopenia, or neutropenia. It was also noted that although, in general, automated measurements of feline platelets can be highly variable, the LaserCyte analyzer’s sensitivity for thrombocytopenia was acceptable.

View the entire abstract (423 KB)

Reference:

1. A Lara, O’Keefe AC, Corn S, Iazbik MC, Russell J, Couto CG. Department of Veterinary Clinical Sciences and Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, 601 Vernon L Tharp, 43210 Columbus OH; IDEXX Laboratories, Westbrook, ME.

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IDEXX VetLab® UA™ Analyzer offers excellent reliability

A comparison study between the IDEXX VetLab UA Analyzer and Bayer’s CLINITEK Atlas® 5001B showed a high level of agreement between the two. In the case of disagreements (there were two largely different readings) reference laboratory results agreed with the IDEXX VetLab UA.

In all, 203 canine, feline and equine samples were analyzed, from both healthy and sick patients. The strips were read visually and automatically. This table summarizes the results.

The study concludes that the IDEXX VetLab UA Analyzer and IDEXX UA Strips provide accurate and reliable semi-quantitative results compared to the Bayer Atlas for canine, feline and equine samples, allowing veterinary practitioners to offer their clients an even more complete diagnostic profile with a quick and easy in-house urinalysis test.

View the entire abstract (93 KB)

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Education and Events

We offer a variety of training events about emerging trends and best practices in veterinary diagnostics in a forum designed to involve, educate and motivate you and your staff. Here are some of the upcoming educational events.

Seminars

• The Most Commonly Misdiagnosed Diseases in Veterinary Medicine
  Fred Metzger, DVM, DABVP

• Management of Retrovirus-Positive Cats
  Susan Little, DVM, DABVP

• Advances in the Diagnosis, Prevention and Treatment of Lyme Disease and Lyme Nephritis
  Richard E. Goldstein, DVM, DACVIM, DECVIM-CA

Visit the education and events calendar to view a full list of current offerings, click the date to view the details, fill out and submit the form to register.

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Choosing an in-house hematology analyzer
Published in the July 2006 DVM NewsMagazine by Fred Metzger, DVM, DABVP

A complete blood count (CBC) is essential to the assessment of the general health status of a patient and the evaluation of potential underlying diseases. A CBC is an integral part of the diagnostic workup of every sick patient, every preanesthetic examination, every senior or wellness profile and every re-evaluation of patients with previous erythrocyte, leukocyte or platelet abnormalities.

The advantage of getting immediate results and providing better patient care is motivating more practices to invest in automated hematology analyzers. Since the advent of the Coulter counter 50 years ago, hematology analyzers have improved substantially, providing more accurate cell counts with automated two-, three- or five-part differential counts and requiring considerably less technician time.

In-house hematology analyzers can be grouped according to technology into quantitative buffy coat (QBC) analysis, impedance counters, and laser-flow cytometers. Because hematology instrumentation can represent a significant investment for a veterinary practice, a strong knowledge of the underlying technology and capabilities of the various analyzers is necessary to make the most informed choice. The QBC method classifies cells based on density and staining of cellular components. Under high-speed centrifugation, blood separates into plasma, the buffy coat (which contains white blood cells [WBCs] and platelets), and the red blood cells. The QBC analyzers are easy to use and very economical, require little to no maintenance and are efficient at screening normal hematology samples. The major disadvantages are the inability to provide a full five-part differential because lymphocytes are grouped with monocytes, and, in felines and equines, the inability to differentiate eosinophils, which are reported in the granulocyte count.

Impedance counters are based on the Coulter principle. The Coulter method of sizing and counting particles is based on the change in resistance as the particles pass through a small aperture between two electrodes. Because cells are classified on size alone, not all WBCs can be differentiated from one another. Nucleated red blood cells and clumped platelets are the same relative size as leukocytes and may be misclassified as WBCs and large platelets, or small clumps of platelets may be counted as erythrocytes.

Another significant issue with impedance-based systems is that they require the use of reagent fluids for normal instrument cycling and involve a considerable amount of maintenance and cleaning, which may increase the price per test. Impedance analyzers are moderately priced and provide fast results, but they cannot provide a true five-part leukocyte differential or reticulocyte count.

Laser-flow cytometry is the most recent and accurate automated cell-analyzer technology and the method used in most reference laboratories to determine the leukocyte differential count. As cells pass through a laser beam, the pattern of light scattered by the individual cells records the cell size, nuclear characteristics and cytoplasmic contents, providing a true optical five-part leukocyte differential. Some analyzers provide an absolute reticulocyte count for dogs and cats, which is the gold standard in classifying anemias. This technology may be slightly more expensive than the other available methodologies and was previously limited only to reference laboratories.

The features of in-house hematology analyzers vary greatly. Practitioners should weigh the pros and cons of each instrument before deciding which one is most appropriate for the practice (Table 1). Regardless of instrumentation, veterinarians should interpret all analyzer results with a peripheral blood film evaluation, which provides invaluable information about the cellular morphologic changes that automated instruments cannot provide. Because hematologic samples are particularly vulnerable to changes over time, in-house analyzers offer the benefits of immediate and reliable information for screening, diagnosing and monitoring your patients’ health.

Table 1: Comparing three types of in-house hematology analyzers

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Can you correctly answer the following questions pertaining to this picture of a peripheral blood film from a dog with a moderate anemia? (Wright's stain, 100x objective field of view, monolayer region of the blood film)

1. Identify the structure indicated.
2. Identify the significance of the presence of this structure in circulation.
3. Indicate whether this anemia is regenerative or nonregenerative.

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