evaluating blood films evaluating blood films - Hungarovet

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PEER-REVIEWEDThree-minute peripheral blood film evaluation:The erythron and thrombonWhen examining the red blood cells and platelets in a blood film, ask yourself these questionsto quickly identify and further characterize conditions such as anemia and thrombocytopenia.Fred L. Metzger Jr., DVM, DABVP(canine and feline practice)Metzger Animal Hospital1044 Benner PikeState College, PA 16801Alan Rebar, DVM, PhD, DACVPDepartment of Veterinary PathobiologySchool of Veterinary MedicinePurdue UniversityWest Lafayette, IN 47907EVALUATING A PERIPHERAL blood film validates cellcounts performed by hematology analyzers,plus it offers valuable diagnostic information relayedby erythrocytes, platelets, and leukocytes.The first article in this symposium describedhow to prepare a peripheral blood film. In thisarticle, we discuss important red blood cell(RBC) and platelet number and morphologicchanges. And in the next article, we discusswhite blood cell (WBC) alterations.If a patient’s RBC mass is reduced, then thepatient is anemic. Once anemia is recognized,the next concern is bone marrow responsiveness:Is the anemia regenerative or nonregenerative?If the RBC bone marrow precursorcells respond with increasedproduction of appropriate magnitude,the anemia is regenerative (responsive). IfRBC production is not effectively increased,the anemia is nonregenerative (nonresponsive).Keep in mind that a lag of 48 to 72hours exists before bone marrow responsivenessis perceived in the peripheral blood, sobe careful in defining nonresponsiveness.Evaluating the thrombon by first assessingplatelet numbers is another important part ofevery complete blood count (CBC). Thrombocytopeniais more common than thrombocytosisand can be of great clinical importance. Plateletcounts below 40,000/µl can lead to spontaneousbleeding. Platelet clumping, which can be seenin any species but is particularly problematic incats, can give a falsely low platelet count.Platelet clumping frequently interferes with resultsfrom impedance cell counters because aggregatedplatelets may be included in the RBC orWBC counts, resulting in artifactually decreasedplatelet counts. 1Our approach to peripheral blood film evaluationuses a question-based format. This systematicapproach allows veterinary practitionersand technicians to maximize important visualinformation.Evaluating the RBCsIs there evidence of RBC regeneration? (Ispolychromasiaor reticulocytosis present?)In dogs and cats, polychromasia is the principalfeature of RBC regeneration on a blood filmprepared with Wright’s or modified Wright’sstain. Polychromatophils are immature RBCs thatstain bluish because they contain RNA (Figure 1).Polychromatophils on blood smears preparedwith Wright’s or modified Wright’s stain roughlycorrespond to reticulocytes on smears preparedwith new methylene blue stain. If regeneration isstill questionable after you’ve evaluated Wright’sstainedblood films, perform a reticulocyte countwith new methylene blue stain.When performing reticulocyte counts in cats,it is important to count aggregate reticulocytes(cells containing diffuse accumulations of reticulum)since they represent recent RBC production1. Polychromatophils (arrows) in a dog (modifiedWright’s stain; 100).FIGURE 18
FIGURE 22. Aggregate (black arrows) and punctuate (red arrows)reticulocytes in a cat. Note that aggregatereticulocytes contain greater than or equal to fivebasophilic specks (new methylene blue stain; 100).4. A nucleated RBC (arrow) in a dog (modified Wright’sstain; 100).FIGURE 4in response to relatively severe anemia (Figure2). In cats, aggregate reticulocytes matureinto punctuate reticulocytes within 12 hours,and punctuate reticulocytes mature into RBCsin about 10 days. Consequently, elevatedpunctuate reticulocytes represent RBC regenerationtwo weeks earlier, whereas aggregatereticulocytes indicate recent regeneration. 2 Indogs and cats, peak reticulocyte counts occurfour to eight days after the onset of anemia.As a general guideline, a reticulocyte countabove 60,000/µl in cats (aggregate only) and80,000/µl in dogs indicates a regenerative anemia.3 Dogs with regenerative anemias havereticulocyte counts that are frequently 100,000to 300,000/µl (dogs with extremely regenerativeanemia can have counts of 500,000/µl orgreater), while cats typically demonstrate aless dramatic response when only the aggregatereticulocyte counts are evaluated.Reference laboratories can provide reticulocytecounts, and in some cases, they willautomatically add the reticulocyte count tothe CBC at an additional charge if anemia isidentified. The newer in-clinic, laser-basedhematology analyzers automatically provideabsolute reticulocyte counts with each CBC. 4Regenerative anemias can be further classifiedas either blood loss or hemolytic (decreasedRBC lifespan) anemias. Whenever yoususpect hemolysis, closely examine RBC morphologyto detect spherocytes, acanthocytes,schistocytes, RBC inclusions, and parasites (seebelow). Figure 3 is a flow chart for classifyinganemias in dogs and cats.Are nucleated RBCs present?Nucleated RBCs, or metarubricytes (Figure4), are not found in any appreciable numbersin mammalian peripheral blood samples. Mostclinicians consider fewer than 4 nucleatedRBCs/100 WBCs to be insignificant when theWBC count is within the reference range. NucleatedRBCs may be seen in increased numberswith strongly regenerative anemias, butthey should always be less numerous than thepolychromatophils or reticulocytes. This findinghas been identified as an appropriate nucleatedRBC response by some clinicians.An inappropriate nucleated RBC responseoccurs when more than 5 nucleated RBCs/100WBCs are present in the absence of polychromasia.Conditions associated with an inappropriatenucleated RBC response include bonemarrow stromal damage, extramedullaryhematopoiesis, fractures, hyperadrenocorticism,feline leukemia virus infection, chemotherapeuticdrug administration, and lead toxi-FIGURE 3Classifying Anemiasin Dogs and CatsWhen a patient has a decreased hematocrit, consider itshydration status and perform a reticulocyte count.The anemia is regenerative if the reticulocyte count is morethan 80,000/µl in dogs and more than 60,000/µl in cats.The anemia is nonregenerative if the reticulocyte count is less than80,000/µl in dogs and less than 60,000/µl in cats. In these cases,perform a serum chemistry profile, urinalysis, and other neededdiagnostic tests to rule out underlying diseases. If no such disease isfound, perform a bone marrow evaluation.Blood loss anemia is apossible cause. Look forexternal or internal hemorrhageorparasites (e.g. fleas,hookworms). Keep inmind that it takes oneto three days to see thehematocrit decrease.Hemolytic anemia is apossible cause. Considerimmune-mediatedhemolytic anemia withspherocytosis or Heinzbody hemolytic anemia(e.g. onion ingestion,acetaminophenadministration).If bone marrow hypoplasiais present, consideranemia of inflammation,anemia of chronic renaldisease, myelophthisisdue to bone marrow disease,or chemotherapytoxicosis.If bone marrow hyperplasiawith ineffectiveerythropoiesis is present,consider a nuclear maturationdefect (FeLV infection,drug toxicosis) or acytoplasmic maturationdefect (lead toxicosis,iron deficiency includingchronic blood loss).9
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