Hematology Case Studies Flashcards
Coombs test
A Coombs test (also known as Coombs’ test, antiglobulin test or AGT) is either of two clinical blood tests used in immunohematology and immunology. The two Coombs tests are the direct Coombs test (DCT, also known as direct antiglobulin test or DAT), and the indirect Coombs test (also known as indirect antiglobulin test or IAT).
The Direct Coombs test is used to test for autoimmune hemolytic anemia; i.e., a condition of a low count of red blood cells (aka RBCs) caused by immune system lysis or breaking of RBC membranes causing RBC destruction.
Corticosteroid-induced or Stress Response
This is likely the most common leukocyte response. Endogenous steroid release or treatment with exogenous corticosteroids results in a leukogram with multiple changes. Lymphopenia is the most consistent change, and mature neutrophilia is usually present. Monocytosis and eosinopenia are expected changes but are more variable. Neutrophilia is due to decreased adherence to the vascular endothelium, which inhibits margination and increases circulating time. As a result, neutrophils may become hypersegmented. There may also be increased marrow release of neutrophils. This response is often misinterpreted as inflammatory.
Excitement or Epinephrine Response
Leukocytosis may occur as a result of exercise or excitement; this response is mediated by increased epinephrine. Epinephrine flushes cells from the marginal to the central pool. The effect may double the total WBC concentration within minutes. In addition, splenic contraction releases WBC and RBC into the peripheral circulation. The leukocytosis is usually due to a mature neutrophilia without a left shift. Lymphocytosis may be present, especially in young horses or cats. The effect in cats is often recognized as a prominent lymphocytosis—as much as double the upper reference limit. The excitement response is relatively uncommon in dogs.
Inflammatory Response
At the beginning of an inflammatory process, the bone marrow responds by blood delivery from its reserve of late-stage maturing neutrophils, including left shift cells. If consumption exceeds marrow delivery during this acute stage, neutropenia with prominent left shift will develop. In dogs and cats, this is an indication of marked severity of the inflammatory lesion, which has historically been characterized as a degenerative left shift. However, strict classification of “degenerative” should be de-emphasized in the interpretation. Of greater importance is that neutropenia with left shift should prompt consideration of a severe inflammatory scenario in dogs and cats.
Subsequently, it takes 2–4 days for the marrow to accelerate neutrophil production by increased stem-cell entry and expansion of proliferative stages that feed the maturation stages and amplify neutrophil delivery to blood. In dogs, the acute stage of the inflammatory response that is mild to moderate neutrophilia is expected, with left shift being somewhat proportional to severity of demand.
After a few days, accelerated production adds to the picture. Neutrophilia may increase along with left shift and toxic change. As the process becomes chronic, the balance between increased marrow output and consumption may favor the development of higher magnitudes of neutrophilia. The most chronic form, present for weeks or months, is described as a “closed cavity” inflammatory process. The lesion becomes somewhat walled-off and therefore consumes fewer neutrophils, yet it still stimulates maximal marrow production. Good examples of closed cavity processes are pyometra in dogs and traumatic reticuloperitonitis (hardware disease) in cows. In these processes, the magnitude of the total WBC concentration, consisting of neutrophilia, may be as high as 100,000/μL of blood in dogs.
In contrast to the inflammatory response in dogs, cattle and most other ruminants have a relatively low reserve of marrow neutrophils and a lower capacity for accelerating granulopoiesis. This is reflected in the relatively low neutrophil concentration in normal ruminant blood. As a result, acute inflammation in cows is characterized by neutropenia that can be profound. Therefore, neutropenia in cattle does not reveal the degree of inflammatory severity. After several days, the marrow response may establish a return of blood neutrophils in modest concentration, characterized by marked left shift and toxic change. This may fit the definition of degenerative left shift but still cannot define severity in cattle. Chronic, closed cavity inflammatory lesions are associated with magnitudes of neutrophilia that rarely exceed 25,000/μL of blood.
Cats and horses are intermediate in these responses, with cats being more like dogs and horses being more like cattle in magnitudes of response. Pigs have an inflammatory response similar to that of dogs.
Monocytosis may occur in the inflammatory pattern at any stage of its progression. Monocytosis is more likely and of greater magnitude when the process becomes chronic.
Combined Steroid and Inflammatory Pattern
Inflammatory disease processes commonly induce a concurrent endogenous steroid response, recognized by the presence of lymphopenia in conjunction with an inflammatory neutrophil pattern. The neutrophil response to inflammation overrides and may be additive to the steroid influence on neutrophils.
Lymphocytosis
Modest lymphocytosis, in the range of 7,000–20,000/μL, should prompt consideration of a possible excitement response, particularly in cats. If that is excluded, then a lymphoproliferative disorder should be considered. If examination of lymphocyte morphology reveals prolymphocytes and/or blasts, then lymphocytic leukemia is the working interpretation. If the cells are all small with normal appearing chromatin, then chronic lymphocytic leukemia is a consideration requiring further workup. Chronic ehrlichiosis may result in lymphocytosis of this magnitude in dogs. At higher concentrations, the lymphocytosis may be regarded as conclusive evidence of leukemia.
Stem-cell Injury Pattern and Pancytopenia
A number of factors may cause reversible or irreversible stem-cell injury. These injuries affect erythroid cell, platelet, lymphocyte, and granulocyte production. Because of short circulation time, neutropenia is often the first abnormality observed. When chronic or irreversible, these injuries result in decreases in all 3 major blood cell lines, with the hemogram demonstrating leukopenia, nonregenerative anemia, and thrombocytopenia. Groups of causes include: 1) overdoses of radiation and antineoplastic drugs; 2) drug or plant toxicities (eg, estrogen toxicity in dogs, bracken fern toxicity in cattle, phenylbutazone toxicity in species other than horses); 3) hematopoietic cell neoplasia involving bone marrow (myelophthisis); and 4) viral infections that injure rapidly dividing cells and may cause transient neutropenia
Eosinophilia and Basophilia
Either eosinophilia or the combination of eosinophilia and basophilia prompts the consideration of the following processes in case management and assessment: allergic-based inflammation, parasitic infestation, subepithelial (skin, respiratory, GI) inflammation that is likely allergic in nature, paraneoplastic induction when common considerations have been excluded. Eosinophilia occurs in most dogs with heartworm disease and may occur in dogs and cats with flea infestation.
Prominent Metarubricytosis
Metarubricytes occasionally become a major component of the total nucleated cell fraction. The magnitude may be 10–50% of the nucleated cell population or more, with absolute numbers reaching 5,000–10,000/μL. This may occur rarely in early phases of an intense regenerative response. It may also be associated with endothelial injury (eg, heat stroke) resulting in abnormal release rate of nRBC from marrow. Most nRBC will be counted as lymphocytes on cell counters with differential capability. This may result in a preliminary result of lymphocytosis that is resolved only by examination of the lymphocyte population on the blood film.
Hematopoietic Cell Neoplasia and Leukemia
Most cases of hematopoietic cell neoplasia of either lymphoid or bone marrow origin will have some number of abnormal cells in blood. Sometimes, neoplastic cells are present in low numbers and are detected only by scanning the blood film under low magnification. Finding abnormal hematopoietic precursor cells in blood in small numbers prompts investigation of marrow and/or other hematopoietic tissues for possible neoplastic disease involvement.
The opposite extreme is marked leukocytosis with a predominance of the abnormal (neoplastic) cell population. In this situation, the blood is diagnostic for leukemia. If poorly differentiated, the cells are classified as blasts, with possible cell lineage based on morphologic appearance. If well differentiated, the cell lineage is usually clearer based on morphologic appearance.
Considerable progress is being made in the use of monoclonal antibody labeling and cytometric analysis to better establish cell lineage, particularly when the morphology is equivocal. This is particularly useful in poorly differentiated leukemias, in which morphology alone is unreliable. The distinction between well-differentiated or chronic myelogenous leukemia and extreme neutrophilic leukocytosis can be difficult
