May 2005 Issue

Featured Case Study: Four-year-old neutered male miniature Schnauzer
by James A. Matthews, DVM, MS, PhD and
Dennis B. DeNicola, DVM, PhD, DACVP

History and Clinical Presentation
Milo had changed owners and was presented to his regular veterinarian by his new owner for a health check. Milo appeared healthy and was current on his vaccinations. He was re-presented to an emergency center two weeks after the health check with a two-day history of anorexia, listlessness and vomiting phlegm. Milo was jaundiced and moderately dehydrated. His abdomen was soft and doughy, and he had a temperature of 100.3°F. Potential differential diagnoses at the time included leptospirosis, intestinal foreign body, chronic active hepatitis and cholangiohepatitis. Abdominal radiographs and an abdominal ultrasound were performed, and blood was collected for an in-clinic CBC and chemistry panel (Table 1). Because Milo's owner is a technologist who works at a veterinary reference laboratory, a second chemistry panel and CBC were also submitted to the veterinary reference laboratory for a direct comparison to the wellness panel (Table 2). A leptospirosis serology panel was requested at the same time (Table 3).

Complete Blood Count Description (two days after initial clinical signs of disease) Erythron—The red cell parameters fell within reference ranges and were unremarkable. Hemolysis was ruled out as a cause of the jaundice. Leukon—Leukocytosis, consisting of a neutrophilia without a lymphopenia, suggestive of an established inflammation Thromon/Platelets—Borderline thrombocytopenia, which was probably due to sample collection/platelet aggregation since there was a small clot found in the tube, and on microscopic examination of the stained blood film, the platelets appeared clumped. There was no clinical evidence of a bleeding tendency, and a coagulation panel was not requested.

Tables 1–3  Click images to enlarge.

Chemistry Panel (two days after initial clinical signs of disease)
The increased alkaline phosphatase and total bilirubin values indicated marked cholestasis, which was likely an intrahepatic cholestasis due to the elevated ALT, indicating hepatocellular injury. There was a marked concurrent azotemia (increased BUN and creatinine), indicating probable multi-organ disease. The degree of azotemia was greater than is typically seen with simple prerenal azotemia, and was more supportive of renal azotemia. A complete urinalysis, including specific gravity determination, would prove helpful in confirming renal azotemia. Amylase increase was most likely associated with decreased glomerular filtration rate (azotemia) and decreased renal clearance of this enzyme. The degree of increased amylase was too small to support active pancreatitis. The mild hyperglycemia was most likely physiologic; however, re-evaluation with repeat chemistry profile was appropriate to determine if there was persistent hyperglycemia.

There was also a markedly increased anion gap on the day of presentation to the emergency center due to the presence of anions that accumulate with renal insufficiency, but are not included in the anion gap calculation ([Na + K] - [TCO₂ + Cl] ). Unmeasured anions, including phosphates, sulfates and small organic acids, are retained during periods of decreased glomerular filtration. Typically during this event, bicarbonate, which is the primary component of the measured TCO₂, is significantly decreased, however, in this case there was also a complicating metabolic alkalosis due to a loss of hydrochloric acid from the stomach (see the marked hypochloridemia). In the body's attempt to maintain electroneutrality, bicarbonate (TCO₂) increases in response to the decreased chloride; the end net result is a near normal TCO₂ value even though there is a significant acid-base disturbance (metabolic titrational acidosis and metabolic alkalosis). There was good correlation between in-house testing and reference laboratory test results (in-clinic laboratory data compared to data in Table 2).

Diagnostic Imaging Findings
Lateral and VD views—Abdominal viscera were well-defined and no significant abnormalities were noted.

Ultrasonographic findings—There was dilation of hepatic and portal veins within the liver. The gall bladder was partially distended, but not obstructed. The stomach and intestines were within normal limits. The renal corticies appeared thickened (7 mm) and hyperechoic, but there was good contrast with the medullary region in both kidneys. Mild dilation of the renal pelvises was also noted. There was a round 1.3-cm hypoechoic mass medial to the right kidney, which was interpreted as a possible enlarged lymph node. The urinary bladder was distended and had no significant abnormalities.

Clinical Diagnosis
Based on the clinical presentation, blood results showing acute severe hepatic and renal disease, and no history of exposure to toxins, canine leptospirosis was the primary differential diagnosis. Milo was begun on intravenous fluid therapy, intravenous antibiotics (amoxicillin) and intravenous Pepcid®. After several days of amoxicillin, Milo was given a course of doxycyclin.

Additional Testing
The original Leptospira serology panel showed a slight positive result against
L. grippotyphosa, which was considered significant since Milo's previous vaccinations had not included a Leptospira bacterin. The second titer run two weeks later showed an eight-fold increase in titer for a serological diagnosis of leptospirosis (Table 3).

A Leptospira polymerase chain reaction (PCR) test was requested, but the sample was not collected until Milo had been on antibiotics for a week. PCR test results came back as negative. Follow-up chemistry panels and CBCs were obtained at 10 days and six weeks after the onset of therapy (Table 2). Several of the more significant serial data changes are presented below in Figures 1–5.

Figures 1–5
    
Click images to enlarge.

Case Outcome
Milo is doing well at home with no apparent long-term effects from his illness. He can now concentrate his urine and other renal profile parameters, and hepatic profile parameters have maintained within the reference range limits.

Discussion
Leptospirosis is a zoonotic disease that has been increasing in incidence in dogs.^1,2,3,4,5 In many ways, Milo had a classical presentation for leptospirosis, including the time of year he presented with illness, since leptospirosis is more common in the warmer, wetter seasons of summer and fall.^2,4,5 Male dogs, like Milo, between four and seven years of age have a slightly higher risk than other dogs.⁴ The common presenting signs of subacute canine leptospirosis include lethargy, anorexia and vomiting.^2,3,5,6 Milo was not febrile, which is not unusual.⁵ Icterus in dogs with leptospirosis is unusual; in one study, only two of 36 dogs were icteric.⁵ In another study, only two of 10 dogs had a bilirubin value greater than 2 mg/dL.⁶

The microscopic autoagglutination test (MAT) is the test most commonly used by reference laboratories to detect antibodies to leptospirosis, however, it takes at least a week after exposure to produce antibodies, and it is difficult to determine if low-positive titers are due to vaccination, previous infection or active infection. Animals suspected of having leptospirosis, but testing negative, should be retested in two to four weeks. A four-fold increase in antibody titer over a two-to-four-week period confirms active infection as long as the animal was not recently vaccinated against leptospirosis.³

Identification of the organism in urine is difficult. Leptospira does not readily stain with common hematology and cytology stains so routine microscopic examination of urine sediment for the organism is rarely useful. Fluorescent antibody (FA) staining of urine sediment, however, has been successful in detecting organisms.^2,3 PCR testing of urine samples for leptospiral DNA is a sensitive and specific test,⁷ however, negative test results may be seen soon after initiating antibiotic therapy.⁸

This is a representative field of view of sediment from a free-catch urine specimen from a seven-year-old neutered male German shepherd with clinical signs of leptospirosis and a Leptospira grippotyphosa titer of 1:12,800. There is a degenerate epithelial cell and coccal bacteria in chains. Notice how difficult it is to visualize the poorly staining spirochetes and distinguish them from mucus. The spirochetes are the thin, pink, thread-like structures distributed throughout the field of view.

In summary, leptospirosis should be considered as a potential differential diagnosis of any dog with renal and hepatic disease, but particularly younger adult dogs. Since identification of leptospiral organisms is difficult, the diagnosis for leptospirosis is often based on a combination of clinical signs, clinical pathologic data and serological testing, although examination of urine by FA and PCR methods may be very helpful as long as the sample is obtained before instituting antibiotic therapy.

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 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.

The Allan H. Hart/IDEXX Scholarship

Once again, IDEXX Laboratories is pleased to announce the Allan H. Hart/IDEXX Scholarship in memory of Dr. Hart, who passed away in May of 1999. In addition to being a respected practitioner, Dr. Hart consulted and traveled the world, sharing his vast knowledge of the practical use of clinical testing. He was a strong proponent of the utility of diagnostic testing in patient management.

In keeping with Dr. Hart's focus, the students awarded the Allan H. Hart Scholarship have a strong understanding of veterinary diagnostics and its practical application to clinical cases. During clinical rotations, they have demonstrated an extraordinary ability to combine clinical laboratory testing with history, physical examinations and ancillary tests to diagnose disease and monitor patient progress.

IDEXX will award a $500 scholarship at each of the U.S. and Canadian veterinary schools to a senior veterinary student who displays exceptional proficiency in diagnostic clinical pathology. Students are nominated by faculty members.

Congratulations to the 2005 recipients of the Allan H. Hart Scholarship from all of us at IDEXX Laboratories! We are honored to recognize their excellence, and wish them the best in their future endeavors.

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Introducing a Breakthrough Innovation for Managing Lyme Disease

A new two-tiered approach to managing Lyme disease in your patients lets you quickly identify Lyme-infected dogs, determine if treatment is warranted and then measure your patient's unique C₆ response, which has been shown to correlate with effective treatment.^9,10 You can also determine if a dog has been re-infected after treatment.

In this new approach, Lyme positive results on the IDEXX SNAP® 3Dx® Test can be followed up with the IDEXX Lyme Quantitative C₆ Antibody Test, which measures B. burgdorferi infection levels in dogs. The new Lyme Quantitative C₆ Antibody Test is offered exclusively at IDEXX Reference Laboratories. It is an ELISA test based on measurement of antibody to the C₆ antigen, the same unique antigen used in the SNAP® 3Dx® in-house screening test. The combination of these assays provides you with the latest diagnostic tools for a new two-tiered approach to managing Lyme disease: an in-house screen with a follow-up quantitative assessment. View the white paper, Diagnostic Testing for Canine Lyme Disease. (205 KB)

Why is it important to quantify a SNAP® 3Dx® positive Lyme result?

• The SNAP 3Dx screen identifies Lyme-positive dogs.
• The Lyme Quantitative C₆ Antibody Test helps you to determine if treatment is warranted.
• Over time, the Lyme Quantitative C₆ Antibody Test allows you to measure changes in C₆ antibody levels.
• Studies have shown that drops in C₆ antibody levels correlate with effective treatment.^9,10

Learn more about the IDEXX Lyme Quantitative C₆ Antibody Test and IDEXX Reference Laboratories.

Learn more about the IDEXX Canine SNAP® 3Dx® Test for heartworm Ag, E. canis Ab and Lyme Ab, including access to a round-table discussion by industry experts on managing Lyme disease and ehrlichiosis.

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Detecting proteinuria

Recently, proteinuria has been shown to be a valuable prognostic indicator of morbidity and death in dogs and cats with kidney disease. Identification of persistent renal proteinuria is a hallmark of glomerular disease. Diagnosing and addressing renal disease before an animal becomes azotemic can allow for early treatment and improvement in patient quality of life.

There are several ways to evaluate urine protein. Urine dipsticks and the microalbuminuria assay lack specificity and sensitivity, and are prone to false-positive and/or false-negative results. Because these tests lack specificity, they should always be followed up by a confirmatory test.

The sulfosalicylic acid (SSA) precipitation test provides an excellent semi-quantitative analysis of urine protein. Unfortunately, this test is inconvenient for in-house use. At IDEXX Reference Laboratories, a confirmatory SSA test is automatically performed on all urinalyses when the dipstick assay is positive for protein.

Regardless of the screening test used, initial discovery of proteinuria requires localization, proof of persistence and tracking of trends via the UPC ratio.

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Education and Events

We offer a variety of seminars and teleconferences 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 educational events in May

• Retrovirus Testing and Management with Jim Richards, DVM
• Tick-Borne Diseases in Dogs with Rick Alleman, DVM, PhD, DABVP, DACVP

Visit the seminar and teleconference calendar, click the date to view the details, fill out and submit the form to register.

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