Quantitative evaluation of echinocytes in the dog

Effects of different drying methods on smears of canine blood and effusion fluid

Background

Glass slide preparations from a variety of specimens (blood, masses, effusions) are commonly made as part of the diagnostic work-up, however the effects of various drying methods in veterinary practice and diagnostic laboratory settings is not clear.

Objective

Compare the effects of four drying methods on results of microscopic examination of canine blood smears and direct smears of pleural or peritoneal effusion fluid.

Methods

Twelve canine blood samples (6 from healthy dogs, 6 from sick dogs) and 6 canine peritoneal or pleural effusion samples. Four smears were prepared from each of the 18 samples and dried using the following methods: air-dry, hair dryer with or without heat, and heat block at 58 °C. Observers, blinded to the drying method, independently reviewed the slides microscopically, using a scoring system to evaluate cell morphology and (for blood smears) echinocyte numbers; scoring results were analyzed statistically.

Results

For blood smears, several comparisons showed more adverse effects on morphology using the heat block method than for one or more other drying methods. For effusion fluid smears, RBCs dried with the heat block or air-dry methods had more poorly preserved morphology than RBCs dried by the hair dryer method without heat.

Conclusions and clinical relevance

The results (1) indicate that different drying methods had a significant effect, (2) support using a hair dryer without heat for both blood smears and effusion fluid smears, and (3) discourage using a 58 °C heat block.

Poikilocytosis in rabbits: prevalence, type, and association with disease

Rabbits (Oryctolagus cuniculus) are a popular companion animal, food animal, and animal model of human disease. Abnormal red cell shapes (poikilocytes) have been observed in rabbits, but their significance is unknown. The objective of this study was to investigate the prevalence and type of poikilocytosis in pet rabbits and its association with physiologic factors, clinical disease, and laboratory abnormalities. We retrospectively analyzed blood smears from 482 rabbits presented to the University of California-Davis Veterinary Medical Teaching Hospital from 1990 to 2010. Number and type of poikilocytes per 2000 red blood cells (RBCs) were counted and expressed as a percentage. Acanthocytes (>3% of RBCs) were found in 150/482 (31%) rabbits and echinocytes (>3% of RBCs) were found in 127/482 (27%) of rabbits, both healthy and diseased. Thirty-three of 482 (7%) rabbits had >30% acanthocytes and echinocytes combined. Mild to moderate (>0.5% of RBCs) fragmented red cells (schistocytes, microcytes, keratocytes, spherocytes) were found in 25/403 (6%) diseased and 0/79 (0%) healthy rabbits (P = 0.0240). Fragmentation and acanthocytosis were more severe in rabbits with inflammatory disease and malignant neoplasia compared with healthy rabbits (P<0.01). The % fragmented cells correlated with % polychromasia, RDW, and heterophil, monocyte, globulins, and fibrinogen concentrations (P<0.05). Echinocytosis was significantly associated with renal failure, azotemia, and acid-base/electrolyte abnormalities (P<0.05). Serum cholesterol concentration correlated significantly with % acanthocytes (P<0.0001), % echinocytes (P = 0.0069), and % fragmented cells (P = 0.0109), but correlations were weak (Spearman ρ <0.02). These findings provide important insights into underlying pathophysiologic mechanisms that appear to affect the prevalence and type of naturally-occurring poikilocytosis in rabbits. Our findings support the need to carefully document poikilocytes in research investigations and in clinical diagnosis and to determine their diagnostic and prognostic value.

Qualitative evaluation of irregularly spiculated red blood cells in the dog

Irregularly speculated red blood cells (IS-RBC) were quantified on fresh blood fixed in glutaraldehyde and were compared to RBC shape changes observed on Wright's-stained blood smears, RBC histograms, and RBC distribution widths (RDW). IS-RBC were infrequently found in healthy control dogs. Twenty dogs with increased IS-RBC were evaluated. The most common clinical diagnoses were lymphosarcoma (seven cases), glomerulonephritis (two cases), hemangiosarcoma (two cases), and chronic liver disease (two cases). Five cases had evidence of disseminated intravascular coagulopathy. In 12 of the 20 cases, keratocytes, schizocytes, and/or acanthocytes were detected in the monolayer area of blood smears. In the other seven cases, keratocytes, schizocytes, and/or acanthocytes were found only in thick areas of the smears. Acanthocytes were the most frequent cell type seen, while schizocytes were absent or present only in low numbers. RBC histograms had a shoulder on the left side of the tracing in six of the 20 cases, suggesting the presence of RBC fragments; however, cases with evidence of platelet aggregation had similar shoulders in RBC histograms. Red cell distribution widths were increased in 12 of the 20 cases with IS-RBC; however, the increase in RDW did not correlate with the presence of schizocytes and was most likely the result of reticulocytosis. This study suggests that quantitative evaluation of RBC shape is a more sensitive method for detection of mild RBC fragmentation when compared to blood smear evaluation, RBC histograms, or RDW. Additionally, acanthocyte-type cells were the most frequent shape change seen in dogs with evidence of RBC fragmentation.

Mechanisms of echinocytosis induced by Crotalus atrox venom

Transient echinocytosis has been reported in association with snake envenomation in humans and dogs. An in vitro model of echinocytosis induced by venom of crotalus atrox (western diamondback rattlesnake) was established to characterize erythrocyte morphologic changes and to investigate potential mechanisms of echinocytic transformation. Erythrocyte morphologic changes produced after the addition of venom to canine, feline, equine, and human blood were characterized by dose-dependent echinocytosis. Type III echinocytosis were consistently induced in vitro at a dose comparable to in vivo envenomation; higher venom doses produced spheroechinocytic and spherocytic transformations. The changes could not be induced in vitro in the presence of ethylenediaminetraacetic acid but were observed in heparinized and citrated blood samples, suggesting the participation of calcium or a metalloprotein in echinocytic change. These findings suggest that phospholipase A2 (PLA2), a calcium-dependent enzyme in snake venom, may be responsible for echinocytic transformation via the production of lysolecithin, a known echinocytic agent. Purified PLA2 from C. atrox venom induced dose-dependent echinocytic change in vitro in canine blood. Other potential mechanisms of echinocytic change evaluated in canine blood included erythrocyte cation loss and erythrocyte ATP depletion. In canine blood mixed with venom, erythrocyte sodium and potassium concentrations were consistently less than those of controls, likely as a result of membrane alteration produced by the actions of PLA2. There was no difference in blood ATP concentrations from dogs with snakebite when compared with normal controls; however, the power of this comparison was low. Echinocytosis induced by rattlesnake venom is related to the degree of venom exposure and may correlate clinically with the amount of venom absorbed. Echinocytic transformation in vitro is induced by PLA2 present in venom.

Echinocytosis associated with rattlesnake envenomation in dogs

A retrospective study of 28 cases of rattlesnake bites in dogs indicated an association of envenomation with echinocytosis; 25/28 dogs (89%) had echinocytosis within 24 hours of a rattlesnake bite being reported. Eighteen of the 28 dogs had marked type III echinocytosis (95-100% of mature erythrocytes affected), and seven dogs had moderate echinocytosis (15-30% of mature erythrocytes affected). The echinocytosis was transient, resolving within 48 hours of envenomation in those for which subsequent blood films were available (13/25). Hypokalemia was noted in 14 of 18 dogs for which biochemical data were available. The hypokalemia was not consistently associated with echinocytosis. The observation of echinocytosis in dogs supports a clinical diagnosis of rattlesnake envenomation.