Immune-mediated hemolytic anemia and thrombocytopenia in a foal

A one-month-old Quarter Horse filly had unilateral epistaxis, hyphema, icterus, petechial hemorrhages in the oral, nasal, conjunctival, and vulvar mucous membranes, anemia, thrombocytopenia, negative antinuclear test result, and a positive direct Coombs' test result. Megakaryocytes or cell-associated IgG (fluorescent antibody and immunoperoxidase stains) were not found in bone marrow biopsy specimens. Treatment consisted of glucocorticoids, antibiotics, and a single whole blood transfusion. The foal responded well to treatment, did not develop relapses of the disease, and was clinically normal one year after treatment.     

Methimazole Treatment of 262 Cats With Hyperthyroidism

The efficacy and safety of the antithyroid drug methimazole were evaluated over a 3-year period in 262 cats with hyperthyroidism. In 181 of the cats, methimazole was administered for 7 to 130 days (mean, 27.7 days) as a preoperative preparation for thyroidectomy. The remaining 81 cats were given methimazole for 30 to 1,000 days (mean, 228 days) as sole treatment for the hyperthyroid state. After 2 to 3 weeks of methimazole therapy (10 to 15 mg/d), the mean serum thyroxine (T4) concentration decreased significantly (P less than 0.001) from a pretreatment value of 12.1 micrograms/dl to 2.1 micrograms/dl. The final maintenance dose needed to maintain euthyroidism in the 81 cats that were given methimazole as sole treatment for hyperthyroidism ranged from 2.5 to 20 mg/d (mean, 11.9 mg/d). Clinical side effects developed in 48 (18.3%) cats (usually within the first month of therapy), which included anorexia, vomiting, lethargy, self-induced excoriation of the face and neck, bleeding diathesis, and icterus caused by hepatopathy. Mild hematologic abnormalities developed in 43 (16.4%) cats (usually within the first 2 months of treatment), which included eosinophilia, lymphocytosis, and slight leukopenia. In ten (3.8%) cats, more serious hematologic reactions developed including agranulocytosis and thrombocytopenia (associated with bleeding). These hematologic abnormalities resolved within 1 week after cessation of methimazole treatment. Immunologic abnormalities associated with methimazole treatment included the development of antinuclear antibodies in 52 of 238 (21.8%) cats tested and red cell autoantibodies (as evidenced by positive direct antiglobulin tests) in three of 160 (1.9%) cats tested.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of the anemia of inflammatory disease in cats with abscesses, pyothorax, or fat necrosis

The purpose of this study was to describe the anemia of inflammatory disease (AID) in cats with naturally-occurring inflammatory diseases, such as abscesses (n = 12), pyothorax (n = 6), and fat necrosis (n = 3). Exclusion criteria were positive FeLV/FIV tests, neoplasia, nephro-, hepato- or endocrinopathies, and blood loss anemia. CBC, clinical biochemistry, measurements of serum erythropoietin, iron, total iron-binding capacity (TIBC), ferritin, acute phase proteins, erythrocytic osmotic fragility (OF), and Coombs' tests were performed. A decrease in hematocrit of 1-28% (median, 10%) occurred within 3-16 days (median, 8 days). The anemia was mild (n = 11), moderate (n = 8), or severe (n = 2). In most cases it was normocytic normochromic, non-regenerative (n = 18), or mildly regenerative (n = 3). Sixteen cats had leukocytosis and 5 mild hyperbilirubinemia. The Coombs' test results were negative for 8 cats and positive for 1 cat. OF was increased in 2 out of 14 cats. Hypoalbuminemia (n = 18) and hyperglobulinemia (n = 16) resulted in a lowered albumin/globulin-ratio in 19 cats. Iron and TIBC were low in 2/19 and 6 /19 cats, respectively. The ferritin concentrations were normal in 7 cats and increased in 12 cats. The acute phase proteins alpha1-acid-glycoprotein and haptoglobin were increased in 14/14 and 13/14 cats, respectively. Erythropoietin was normal (n = 4), mildly increased (n = 7) or severely increased (1). Two cats were euthanized due to their underlying disease, 3 cats needed blood transfusions. AID in cats is usually mild to moderate, non-regenerative, and normocytic normochromic. It can be clinically relevant causing severe and transfusion-dependent anemia. AID seems to be multifactorial with evidence of iron sequestration, decreased RBC survival, and insufficient erythropoietin production and bone marrow response. Specific and supportive therapy, including transfusions, can reverse these processes.     

Pemphigus foliaceus in association with systemic lupus erythematosus, and subsequent lymphoma in a cocker spaniel

A seven-year-old neutered male cocker spaniel was presented with an 11-month history of generalised bacterial dermatitis. There were skin lesions over the entire body, which were round, slightly raised and encrusted. Skin biopsies were collected and the histological findings were consistent with pemphigus foliaceus. Immunohistochemical staining by the indirect immunoperoxidase method was positive, with desmosomal deposition of immunoglobulin (Ig) G. Haematological analysis revealed a regenerative anaemia and profound thrombocytopenia, while a Coombs' test was positive for polyvalent canine Coombs' reagent and anti-dog IgG. An antinuclear antibody test was positive, with a titre of 10,240. An ophthalmic examination demonstrated low tear production (keratoconjunctivitis sicca). Seven months after initial referral, the dog was re-presented with severe generalised peripheral lymphadenopathy. Radiographic evaluation of the thorax and abdomen revealed enlarged cranial mediastinal and sublumbar lymph nodes. Tru-Cut biopsy from an enlarged lymph node confirmed the diagnosis of lymphoma, which was phenotyped as a B-cell tumour. The diagnosis in this case was systemic lupus erythematosus, with the unusual feature of pemphigus foliaceus, and subsequent development of B-cell lymphoma. The case adds further to knowledge of the protean clinical presentations of canine autoimmune diseases and provides additional evidence for the potential association between autoimmunity and immune-system neoplasia in this species.     

Progressive polysystemic immune-mediated disease in a dog

A dog with polyarthritis, angular joint deformities, and a high serum antinucleolar antibody titer was treated over a period of 20 months. During the clinical course, leukopenia, thrombocytopenia, Coombs' positive hemolytic anemia, and a pemphigus-type skin disorder developed, all of which responded to immunosuppressive therapy. It is not known whether the polysystemic disease in this dog represents a pleomorphic manifestation of canine systemic lupus erythematosus or multiple autoimmune disorders occurring in the same animal.     

Primary immune-mediated hemolytic anemia in 19 cats: diagnosis, therapy, and outcome (1998-2004)

Immune-mediated hemolytic anemia (IMHA) occurs less frequently in cats than in dogs. The value of the Coombs' test (CT) has been questioned, but detailed surveys of its use are lacking. The objective of this study was to describe 19 cats with primary IMHA (pIMHA) and to examine the diagnostic value of the direct CT. The CT was performed in 92 cats; it was negative in 5 healthy, in 9 sick nonanemic, and in 55 cats with different types of anemia. The CT was positive in 18 anemic cats (2 feline leukemia virus (FeLV) positive, 1 with cholangiohepatitis, 15 with no underlying disease). Moreover, agglutination persisted after saline washing in 5 anemic cats (1 lymphoma, 4 pIMHA). Inclusion criteria for pIMHA were a positive CT (15) or persistent agglutination (4), and the exclusion of other diseases. The age of the 19 cats ranged from 0.5 to 9 years (median, 2 years); male cats were overrepresented. The PCV on admission was 6-22% (median, 12%). The anemia was nonregenerative in 11 cats. Additional abnormal laboratory results were leukocytosis (2), lymphocytosis (6), hyperbilirubinemia (13), hyperglobulimemia (10), and increased liver enzyme activities (10). Initial treatment consisted of blood transfusions (10), crystalloids (11), prednisolone (19), antibiotics (19), and H2-blockers (11). Four of 17 cats were euthanized 9, 63, 240 and 2,160 days after initial presentation (mortality rate, 23.5%). Relapses were reported in 5 of 16 cases (31%). Thus, pIMHA appears to occur more frequently than recognized previously, with a more favorable prognosis in cats than in dogs. The CT was useful in identifying immune-mediated pathogenesis.     

Immune mediated skin lesions in a dog with autoimmune hemolytic anemia

A canine case of Coombs' test positive and antinuclear antibody-negative hemolytic anemia was examined because of the development of skin lesions after 18 months treatment with prednisolone. Histopathological examination of biopsy specimens obtained from skin and oral mucosa revealed the acantholysis, edematous lesions of the stratum basale and mononuclear cell accumulation in the dermis. Deposits of immunoglobulin G and complement factor 3 were detected at the intercellular and dermoepidermal junction by the direct immunofluorescent test. From these results, the case was considered to be an autoimmune disease caused by distinct antibodies against different organs.     

Experimental visceral leishmaniasis in the owl monkey

Visceral leishmaniasis developed in eight owl monkeys (Aotus trivirgatus) after intravenous inoculation with a Khartoum strain (WR378) of Leishmania donovani. Six monkeys died within 93 days, and two monkeys recovered from the disease. Clinically, signs were weight loss, anemia, and hepatosplenomegaly. Hematologic findings included anemia, granulocytopenia, thrombocytopenia, and lymphocytosis. Analysis of serum or plasma revealed hyperbilirubinemia, azotemia, hyperglobulinemia, hypoalbuminemia, and altered hemostasis. All monkeys developed positive antibody titers to promastigotes of L. donovani and had increases in immunoglobulins M and subsequently G. Liver, spleen, bone marrow, and lymph nodes were the principal organs containing numerous parasitized macrophages. The owl monkey was highly susceptible to L. donovani infection and should be a useful animal model for the study of visceral leishmaniasis.     

Expression, bioactivity, and clinical assessment of recombinant feline erythropoietin

OBJECTIVE: To determine the activity of recombinant feline erythropoietin (rfEPO) in murine bioassays and evaluate its efficacy and safety in cats with erythropoietin-dependent nonregenerative anemia. ANIMALS: 26 cats (group 1, 19 cats with anemia attributed to chronic kidney disease [CKD]; group 2, 7 cats with CKD and recombinant human erythropoietin [rhEPO]-induced red cell aplasia [RCA]). PROCEDURE: The rfEPO was synthesized by use of Chinese hamster ovary (CHO) cells transfected with feline erythropoietin complementary DNA. Preclinical assessments of rfEPO included an erythroid cell proliferation assay and measurements of reticulocytosis in Balb/C mice. Clinical assessments of cats included hematologic, biochemical, and clinical examinations during 12 (group 1) or 6 (group 2) months of rfEPO treatment. RESULTS: Biological activity of rfEPO was broadly equivalent to rhEPO in preclinical murine bioassays. Median Hct and absolute reticulocyte count in cats increased significantly during the first 3 weeks of rfEPO treatment, and median Hct generally could be maintained within a target range of 30% to 40% with periodic adjustments of rfEPO doses. Unexpectedly, 5 cats in group 1 and 3 cats in group 2 that initially responded to rfEPO treatment again developed anemia that was refractory to additional rfEPO treatments, even at higher doses. CONCLUSIONS AND CLINICAL RELEVANCE: Treatment with rfEPO can reestablish active erythropoiesis in most cats with CKD, even those with anemia attributable to rhEPO-induced RCA. Unfortunately, development of RCA during treatment with CHO cell-derived recombinant erythropoietin proteins was not eliminated as a serious safety concern, even for this feline-specific preparation.     

Systemic toxicosis associated with azathioprine administration in domestic cats.

Five cats were treated with an azathioprine suspension (2.2 mg/kg of body weight on alternate days) and 2 cats were given vehicle (controls) for 9 weeks. Complete blood and platelet counts and serum biochemistry variables were monitored weekly. Bone marrow aspirates were evaluated every 3 weeks, and core bone marrow biopsy was performed at the end of the study. Profound neutropenia (less than 600 cells/microliters) was observed in all treated cats, and 1 cat developed pancytopenia. Treatment was discontinued if the WBC count was less than 3,000 cells/microliters. Four weeks after discontinuation of azathioprine, 1 treated cat again was given azathioprine at a lower dosage (1.1 mg of azathioprine/kg on alternate days) and neutropenia recurred within 2 weeks. During treatment, 3 cats developed thrombocytosis, and 2 developed thrombocytopenia. In 4 of 5 cats, neutropenia and thrombocytopenia resolved when azathioprine was discontinued. Bone marrow cytologic examination during treatment revealed reduction of the neutrophil line, with relative increase in monocytes. Core bone marrow biopsy at the completion of the study revealed hypocellular marrow with marked decrease in the myeloid series in cats given azathioprine. One of the cats that was treated with azathioprine had a hypercellular marrow with increased numbers of mature granulocytes and precursors; however, azathioprine had been discontinued 3 weeks prior to biopsy. Alterations in serum biochemical variables were not associated with azathioprine. Two cats that were treated with azathioprine developed respiratory tract infections, and 1 of them was euthanatized during the study.     

Hematologic Toxicosis Associated with Doxorubicin Administration in Cats

The hematologic toxicity of doxorubicin, 30 mg/m2 body surface area (BSA) every 21 days to a cumulative dose of 300 mg/m2, was evaluated in six cats. Complete blood and platelet counts were performed daily during the first treatment cycle. They were monitored before treatment for all remaining cycles, and at the average neutrophil nadir (day 8) starting with cycle 4. Significant poikilocytosis developed after the first treatment and remained throughout the study, although anemia did not occur. No other red blood cell abnormalities were seen. Platelet counts remained within the reference range throughout the first treatment cycle, but mild thrombocytopenia (88,000-288,000/uL) was found in 11.3% of subsequent complete blood counts (CBCs). Thrombocytosis was seen in 30.9% of CBCs. Neutropenia did not occur during the first treatment cycle although neutrophil counts did decrease, with the nadir occurring between days 8 and 11. All neutrophil counts returned to pretreatment values by day 14. Neutropenia was documented after 14 of 46 (30.4%) doxorubicin treatments, and was associated with fever in 5 cats (10.9%). All fevers responded to oral antibiotic therapy. Neutropenia that lasted more than 14 days developed in two cats, necessitating dosage reduction to 25 mg/m2 BSA. At the dose used in this study, doxorubicin administration was associated with acceptable hematologic toxicosis in most cats.     

Congestive heart failure associated with hyperthyroidism in cats

Hyperthyroidism was diagnosed in 4 cats with congestive heart failure. Dyspnea and anorexia were observed in 3 of the 4 cats. In each cat, a holosystolic left and/or right apical heart murmur was auscultated. In 3 cats, a prominent extra heart sound (gallop rhythm) was auscultated. All cats had a palpably large thyroid lobe(s) and weight loss. The laboratory and ECG changes were similar to those reported for feline hyperthyroidism. Moderate-to-severe pleural effusion and cardiomegaly were detected via radiography in all cats. Some cats had radiographic signs of pulmonary venous engorgement and pulmonary edema. Echocardiography revealed cardiac dilatation and low left ventricular shortening fraction (wall motion) in all cats. Three cats responded initially to cardiac drugs and propylthiouracil or thyroidectomy. One of these died later, presumably from an adverse reaction to propylthiouracil, and the others died from recurrent congestive heart failure (1) or postoperative cardiac arrest (1). One cat did not respond to treatment, and died 2 days after diagnosis.     

Presumed primary immune-mediated thrombocytopenia in four cats

Feline primary immune-mediated thrombocytopenia (pIMT) is a rare hematological disorder. Platelet-bound antibody assays for cats have variable specificity and sensitivity and are not widely available. Diagnosis of pIMT is made on the basis of exclusion of other identifiable causes of thrombocytopenia and the response to immunosuppressive therapy. This report describes four cats with severe thrombocytopenia and no detectable underlying disease. One cat was euthanased because of pulmonary hemorrhage, while the other cats had frequent relapses, two of these cats developed diabetes mellitus due to long-term corticosteroid therapy. In these cats IMT had a chronic course and responded poorly to therapy with prednisolone. Alternative immunomodulatory drugs may be considered in the treatment of feline IMT.     

Quantitative studies of erythropoiesis in the clinically normal, phlebotomized, and feline leukemia virus-infected cat

Erythropoiesis was evaluated in 5 cats at base line with normal PCV and then in the same cats with anemia induced by phlebotomy and in 5 other cats with nonregenerative anemia from community-acquired feline leukemia virus (FeLV) infection. The hematologic evaluation included complete blood cell and reticulocyte counts, marrow morphologic features, determination of serum erythropoietin concentrations by radioimmunoassay, ferrokinetic studies, and in vitro marrow culture of early erythroid progenitors (erythroid burst-forming units; BFU-E) and late erythroid progenitors (erythroid colony-forming units; CFU-E). Phlebotomized cats developed marrow erythroid hyperplasia and an increased reticulocyte count. Ferrokinetic studies revealed an increase in plasma iron turnover from 1.4 to 3.8 mg of Fe/dl of blood/day and RBC use from 50.4% to 78.5%. The mean CFU-E number and CFU-E/BFU-E ratio increased after phlebotomy, but the increase was not significant (P greater than 0.05). Serum erythropoietin values did increase significantly. In FeLV-infected cats, a nonregenerative anemia was demonstrated by marrow erythroid hypoplasia and a low total reticulocyte count. An increased percentage of rubriblasts and prorubricytes was observed in 4 of the 5 cats. Although serum erythropoietin values were high (321 +/- 123 mU/ml vs normal 14 +/- 1 mU/ml), ferrokinetic data revealed decreased erythropoiesis. Marrow culture studies in the FeLV-infected cats also revealed low numbers of BFU-E and CFU-E, but normal numbers of granulocyte-macrophage progenitors remained. Seemingly, the FeLV infection impaired the ability of feline marrow to respond physiologically to anemia.     

Disseminated intravascular coagulation in experimentally induced feline infectious peritonitis

Disseminated intravascular coagulation was induced in kittens by intraperitoneal inoculation of feline infectious peritonitis virus (FIPV). Kittens seronegative to FIPV survived significantly (P less than 0.05) longer than those seropositive to FIPV. Pyrexia, anemia, icterus, hyperbilirubinemia, and elevated concentrations of liver-specific enzymes were detected in the inoculated cats. Lesions induced included disseminated fibrinonecrotic and pyogranulomatous inflammation, hepatic necrosis, and widespread phlebitis and thrombosis. Localization of FIP viral antigen and immunoglobulin G was demonstrated in foci of heptic necrosis by immunofluorescence miroscopy. Lymphopenia, thrombocytopenia, hyperfibrinogenemia, and increased quantities of fibrin-fibrinogen degradation products were present in cats after the onset of clinical illness. Depression of factor VII, VIII, IX, X, XI, and XII plasma activities and prolongation of prothrombin and partial thromboplastin times also developed in infected cats. The accelerated onset of clinical disease and mortality in seropositive kittens vs seronegative kittens and the association of virus and antibody in multiple foci of hepatic necrosis suggest an immune-mediated component is involved in the pathogenesis of this disease.     

Hematologic abnormalities and outcome of 16 cats with myelodysplastic syndromes

We investigated the hematologic abnormalities and prognoses in 16 cats with myelodysplastic syndromes (MDS). Nonregenerative anemia, thrombocytopenia, and neutropenia were observed in 15, 13, and 4, respectively, of the 16 cats with MDS. Morphologic abnormalities characteristic of MDS included megaloblastoid rubricytes (9 cats), hyposegmentation of neutrophils (7 cats), nuclear abnormality of rubricytes (10 cats) and neutrophils (13 cats), and micromegakaryocytes (10 cats). Disease in these 16 cats was subclassified into refractory anemia (RA; 8 cats), RA with excess of blasts (RAEB; 5 cats), RAEB in transformation (RAEB in T; 1 cat), and chronic myelomonocytic leukemia (CMMoL; 2 cats), according to the human French-American-British (FAB) classification. In the cats in which the clinical outcome was known, 3 of 6 cats with high blast cell count MDS, including RAEB, RAEB in T, and CMMoL, developed acute myeloid leukemia, but only 1 of 8 cats with low blast cell count MDS (RA) developed acute myeloid leukemia. Based on the Dusseldorf scoring system for the prognosis of human MDS, the survival times of the cats showing high scores (> or =3 points) were significantly shorter than those of the cats with low scores (<3 points). The FAB classification and Dusseldorf scoring system were considered to be useful for predicting the prognosis of feline MDS. Furthermore, 15 of the 16 cats with MDS in this study were infected with feline leukemia virus, indicating its possible etiologic role in the pathogenesis of feline MDS.     

Systemic lupus erythematosus in a filly

Systemic lupus erythematosus (SLE) was diagnosed in a 2-year-old Standardbred filly. Clinical signs of SLE included weight loss, bilateral symmetric alopecia, seborrhea, oral ulceration, and lymphadenopathy. Abnormal laboratory findings included a Coombs test-positive hemolytic anemia and positive antinuclear antibody test result. Histologic evaluation of multiple skin biopsy specimens revealed interface dermatitis with linear deposition of IgG at the basement membrane zones of the epidermis and hair follicles. The filly did not respond to glucocorticoid treatment and was euthanatized. Necropsy findings included membranous glomerulonephritis and fibrous synovitis. On the basis of these findings, SLE should be considered in the differential diagnosis of immune-mediated skin disease in horses. Definitive diagnosis of SLE relies on recognition of multisystemic disease and confirmatory histopathologic and immunopathologic findings.     

Molecular evidence supporting Ehrlichia canis-like infection in cats

Currently, the pathogenic role of Ehrlichia canis in cats has been proposed predominantly on the basis of the serologic evidence of natural infection and the infrequent detection of morulae-like structures within the cytoplasm of leukocytes in cats. The purpose of this report was to provide molecular evidence supporting E. canis-like infection in 3 cats that had clinical manifestations consistent with canine ehrlichiosis but lacked antibodies to E. canis antigens. Serum from all 3 cats contained antinuclear antibodies (ANAs). The predominant disease manifestation was polyarthritis in 1 cat and bone marrow hypoplasia or dysplasia. accompanied by pancytopenia or anemia and thrombocytopenia, in 1 cat each. The alignment of E. canis partial 16S ribosomal DNA (rDNA: 382 nucleotide positions), amplified from EDTA blood samples from each cat, was identical to each other and was identical to a canine isolate of E. canis (GenBank accession number AF373613). In 1 cat, concurrent treatment with corticosteroids may have interfered with the therapeutic effectiveness of doxycycline for the elimination of E. canis-like infection. To further define the spectrum of ehrlichiosis in cats, polymerase chain reaction (PCR) testing may be necessary until serologic testing is thoroughly validated in experimentally or naturally infected cats. In addition, until E. canis has been isolated from cats and several tissue culture isolates are available from disparate geographic regions for detailed comparative genetic study, the molecular evidence presented in this study supporting E. canis-like infection in cats must be interpreted with caution.     

Total parenteral nutrition in clinically normal cats

Seven clinically normal cats were maintained on total parenteral nutrition (TPN) with nothing given PO for 2 weeks. The TPN solution consisted of a mixture of dextrose, amino acids, soybean oil emulsion, electrolytes, and vitamins. Three cats were fed calories in excess of published maintenance requirements, and they gained some weight, vomited occasionally, had oral ulcerations, and had signs of depression after 10 to 13 days on TPN. Four cats that were not overfed did well clinically and maintained stable body weights. All cats developed anemia and thrombocytopenia to varying degrees during TPN administration and had polyuria and serum triglyceride concentrations higher than normal fasting values. Some cats had changes in liver-specific biochemical variables. Hepatocellular swelling and vacuolation and small intestinal villous atrophy and fusion were the most common histopathologic changes seen after TPN. These changes were reversible when TPN was discontinued and the cats were returned to enteral nutrition.     

Isotype-specific antibodies in horses and dogs with immune-mediated hemolytic anemia

Classes of antibody bound to erythrocytes were determined using direct immunofluorescence (DIF) flow cytometry in 3 horses and 12 dogs with immune-mediated hemolytic anemia (IMHA). Background levels of antibody binding were determined in samples from 12 horses and 12 dogs that were free of clinical disease. The range of nonspecific binding of a fluorescein isothiocyanate (FITC)-conjugated goat anti-equine immunoglobulin G (IgG) was 19.9–36.7%, but was eliminated by the use of the F(ab)₂ fragment of FITC-conjugated goat anti-equine IgG. Background binding by other class-specific antibodies to equine and canine erythrocytes was negligible. The DIF results were compared to the direct antiglobulin (Coombs) test in 5 horses and 20 dogs with anemia. The former assay was more sensitive in dogs with IMHA than was the Coombs' test (100% versus 58%). In contrast, the Coombs' test had better specificity than the DIF assay (100% versus 87.5%, respectively). Using clinical parameters or response to therapy as the comparison, the positive and negative predictive values for the DIF test were 92% and 100% compared to the values of the Coombs' test of 100% and 62%. The DIF assay detected low levels of cells bound with antibody (<30%) in 5 dogs that were Coombs' test-negative. For both species, performance of the DIF test was independent of the prozone effect. Five dogs with IMHA had IgG and IgM on erythrocytes, 5 had IgG, and 2 had IgM. Three horses had surface-bound IgG, including a horse with suspected penicillin-induced IMHA, a foal with neonatal isoerythrolysis, and a foal with clostridial septicemia. The DIF method was valuable in monitoring the response to therapy in the foal with neonatal isoerythrolysis.