December 2006 Issue

Featured case study:
Five-year-old neutered domestic shorthair cat, Sammy, had not been eating well for three or four days, was sleeping more than usual and was not as playful as in the recent past
by Dr. Annette Cowell of the Cat Clinic of Stillwater, Stillwater, Oklahoma

Differential diagnosis
Based upon the relatively sudden onset of clinical signs and these physical findings, the primary differential was sudden onset anemia. Clinical signs and physical findings were not sufficient to characterize the anemia, and emergency diagnostic laboratory testing was discussed with the owners.

Plan
Sammy's initial work-up included collecting blood for a complete blood count (CBC) and general health chemistry profile. Follow-up diagnostic testing would be planned following review of this preliminary data collection.

Day 1
Laboratory data

Low PLT statistics. Distribution parameter not reported. (RB 3)

Erythron—There is a mild to moderate, normocytic, normochromic anemia. Based upon the reticulocyte count reported by the LaserCyte® analyzer, this anemia can be classified as non-regenerative; however, the LaserCyte, like other automated reticulocyte counters available in commercial and academic laboratories, only count aggregate reticulocytes. In the cat, anemias with a HCT greater than 20% aggregate reticulocytes typically are not released from the marrow; only punctuate reticulocytes are released in many of these milder anemias seen in the cat. Detailed microscopic evaluation of a New Methylene Blue stained sample from this animal should be considered to ensure that there is no bone marrow response at this time. Before condemning the marrow as failing to respond, it is also important to remember there is a lag phase for the bone marrow response; this lag phase could take a minimum of 48 to 72 hours. This animal’s clinical signs were not noted three or four days before presentation; the anemia may be in the very early stages of development. If possible, complete characterization of the marrow’s ability to appropriately respond should wait for one to two days from the time of presentation.

On microscopic evaluation of the peripheral blood film, multiple erythrocytes had small, round to oval, “signet ring”, 1.0–1.5 micrometer structures or bipolar, 1.0–2.0 micrometer, oval “safety pin” appearing structures. These structures are consistent in morphology with Cytauxzoon felis merozoites. This disease causes an acute nonregenerative anemia typical of that seen in the hematology results.

Leukon—There is a mild leukopenia with a low normal neutrophil and lymphocyte count. A glucocorticoid influence (“stress”) is likely based upon the low normal (within reference interval) value for the lymphocytes, and the clinical presentation and the low normal (within reference interval) neutrophil count may be associated with a consumption of neutrophils associated with inflammation. Serial CBC evaluations will be required to better characterize the leukocyte dynamics in this animal. There was no left shift or neutrophil toxicity noted when the peripheral blood film was examined microscopically.

Thrombon—Platelets are severely decreased; no platelet clumping was noted on the peripheral blood film examination to suggest a false thrombocytopenia. The failure in reporting any platelet indices is most likely related to the low number of events (low platelet count) available for accurate characterization.

Bilirubin—There is a moderate hyperbilirubinemia that is potentially associated with hemolytic disease where the rate of red blood cell destruction is greater than the capacity of the liver to handle the bilirubin from the hemoglobin breakdown or associated with a dysfunctional liver that cannot process the bilirubin breakdown product normally. The finding of Cytauxzoon organisms within erythrocytes and the anemia present clearly suggest that hemolytic disease is likely present. Also, it is likely that part of the increase in bilirubin is due to hepatic dysfunction or intrahepatic cholestasis, since many of the clinical signs seen with cytauxzoonosis are due to schizonts and not the piroplasms. Cytauxzoon organisms undergo schizogomy in macrophages throughout the body, and the macrophages are greatly enlarged due to the presence of developing merozoites and occlude the lumen of venules throughout the body. These macrophages likely interfere with hepatic blood flow resulting in hepatic dysfunction and increased bilirubin levels. Since there is no decreased BUN or glucose, and Albumin and Cholesterol are in the low end of the reference interval limits but not below the lower limit value, chronic hepatic disease and resultant hepatic insufficiency are less likely to be the cause of the hyperbilirubinemia.

Glucose—There is a mild hyperglycemia that is most likely physiologic hyperglycemia. The extreme low within reference interval lymphocyte count is suggestive of a glucocorticoid influence, which could easily explain the mild hyperglycemia noted. The glucose value is not high enough for consideration of Diabetes at this time.

Final diagnosis
Cytauxzoonosis (pancytopenia, hyperbilirubinemia, and hyperglycemia as seen in this case are frequently seen in cats with cytauxzoonosis)

Therapeutic plan and progress
Cytauxzoonosis is an extremely serious and commonly fatal protozoal disease of cats found endemically in the south central and southeastern portions of the United States. Because of the seriousness of the disease process and the need for critical care management, Sammy was referred to Oklahoma State University Center for Veterinary Health Services. Sammy died within 24 hours of admission to the Center for Veterinary Health Services despite intensive supportive care, including experimental antiprotozoal medications.

Note: Cytauxzoonosis is typically associated with a rapid onset illness with an associated mortality rate of greater than 95%. The domestic cat is likely a dead-end host for this organism and the natural reservoir for Cytauxzoon felis is the North American bobcat. The Ixodid tick Dermatocentor variables and possibly other species of ticks can transmit the organism from bobcats to domestic cats, and as one may expect, infections are more commonly seen between May and September, which is the active period for these ticks. It is of interest to note that Sammy presented to The Cat Clinic of Stillwater at the beginning of October. Sammy lived next to the golf course where bobcats had been observed by area residents.

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.

back to the top    

back to the top    

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

• Canine Pancreatitis Diagnosis and Management
  Jðrg M. Steiner, med.vet., Dr.med.vet., PhD, DACVIM-SA, 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.

back to the top    

Lactate Measurement as an Indicator of Perfusion
by Michael H. Karagiannis, DVM; Alisa N. Reniker, DVM, DACVECC; Marie E. Kerl, DVM, DACVIM, DACVECC; F.A. Mann, MS, DVM, DACVS, DACVECC
University of Missouri—Columbia

This article discusses the use of plasma or blood lactate measurements as valuable diagnostic information in the treatment of critically ill patients. While there are other causes of hyperlactatemia besides tissue hypoxia (which causes anaerobic metabolism, which in turn increases lactate production), and sample collection can affect results, the authors agree that serial blood lactate measurements can guide treatment by indicating improvements in tissue oxygenation as well as provide prognostic information. Used in human medicine for more than 30 years, measurement of blood lactate as an indirect indicator of tissue oxygenation is relatively new in veterinary medicine. The availability of inexpensive and easy-to-use lactate measurement tools has made serial measurements in critically ill veterinary patients more common. Blood lactate measurement is a useful tool in assessing global perfusion, determining the severity of certain conditions and in helping doctors to determine treatment. The article discusses in detail the physiological conditions that occur through lactate production and metabolism, the effects on the body when things go wrong and the causes—such as shock—of disruption to the normal cycles. Conditions such as lactic acidosis and hyperlactatemia are also explained.

Other indirect measurements of tissue oxygenation—such as saturated oxygen concentration, partial pressure of venous oxygen and oxygen extraction ratio and gastric tonometry—can require time and specialized equipment and are often costly. Also, in some cases, as in the prediction of mortality, lactate measurement has been found to be more useful. The article notes that point-of-care lactate measurement allows samples to be run within a 30-minute time frame, eliminating concern of elevated lactate concentrations due to glycolysis.

The measurement of lactate can provide useful diagnostic and prognostic information when differentiating conditions, assessing the severity of certain conditions and determining the need for blood transfusions in anemic patients. Trending lactate measurements can be used to show response to treatment as well as success of resuscitation measures, though the article warns that for resuscitation endpoints, other perfusion parameters should be checked as well, such as heart rate, blood pressure, urine output and pulse rate.

Karagiannis, MH. Lactate Measurement as an Indicator of Perfusion. Compendium.
2006;28(4):287–298.

back to the top    

The IDEXX VetStat® analyzer provides accurate, reproducible electrolyte results

In a recent study, canine, feline and equine whole-blood samples were analyzed at 15 different laboratories including practices, a top U.S. veterinary hospital and our own research-and-development laboratory.* From these locations, we investigated the IDEXX VetStat Electrolyte and Blood Gas Analyzer performance on sodium, potassium and chloride by comparing VetStat results to results from an ion-selective electrode system—a recognized reference methodology.

Based on the study findings, the VetStat® analyzer gives accurate and reproducible results on veterinary whole-blood samples compared to ion-selective electrode methodology. Performance characteristics were considered acceptable for use with canine, feline and equine samples.

View the entire abstract (700 KB)
*M.D. Jensen, M. Kahn

back to the top    

The IDEXX VetStat® blood gas results correlated well with electrode methodology

In a comparison study between the IDEXX VetStat Electrolyte and Blood Gas Analyzer and the AVL995 pH/Blood Gas Analyzer*, we investigated the VetStat analyzer performance on pH, PCO₂ and PO₂ by comparing VetStat results to results from the AVL electrode system—a recognized reference methodology.

Based on the study findings, measured VetStat® analyzer results correlated well with those from the AVL995 electrodes. Performance characteristics were considered acceptable for use with canine, feline and equine samples.

View the entire abstract (693 KB)
*M.D. Jensen, M. Kahn

back to the top    

NOW with FREE CE Credit!

Have you taken advantage of every qualifying Interactive Challenge for FREE CE credits?

Every Interactive Challenge from June 2006 on has been worth 0.5 CE credits—that's three credits so far this year—and you get the credits just for participating! Check out the Diagnostic Edge archive and take any qualifying challenges you may have missed, don't let these fun credits slip away!

Can you correctly identify the two structures indicated in this high dry field of view (40x objective field of view) of the sediment of urine with an alkaline pH from a dog, Wright's stain preparation?

1. Identify the structure indicated.
2. Identify the structure indicated.

Not a Diagnostic Edge subscriber? Subscribe now!

All fields are required for CE credit records.

Thanks for taking the Diagnostic Edge Interactive Challenge!

*Each interactive challenge meets the requirements for 0.5 hours of continuing education credit in jurisdictions that recognize AAVSB’s RACE approval, however, participants should be aware that some boards have limitations on the number of hours accepted in certain categories and/or restrictions on certain methods of delivery of continuing education.

AAVSB Provider Number 106

Not a Diagnostic Edge subscriber? Subscribe now!

back to the top