In cats, non-regenerative anaemia may be commonly seen in chronic renal disease, but also occurs with infections with Mycoplasma spp, Cytauxzoon spp, FeLV and FIV, as well as in association with immune-mediated haemolytic anaemia, myelodysplastic syndrome, pure red cell dysplasia and iron deficiency.
The clinical signs associated with anemia in cats include pale mucous membranes, weakness, collapse, lethargy, exercise intolerance, tachypnea, and tachycardia. Many of these are attributable to hypoxia.
A systolic heart murmur may be appreciated on auscultation as a direct result of turbulent blood flow related to decreased blood viscosity. The severity of observed clinical signs may correlate with the duration of anemia; signs of acute anemia are typically more severe than those of chronic anemia
Diagnosis can be ascertained by hematological analysis, bone marrow assessment and iron level studies.
A CBC with a reticulocyte count and blood smear can be helpful in determining the etiology of anemia. Most cases of nonregenerative anemia have normal RBC indices and are normocytic and normochromic. However, microcytosis can occur with iron-deficiency anemia, and macrocytosis may accompany FeLV-induced anemia.
In contrast, most cases of regenerative anemia in cats are macrocytic and hypochromic due to the abundance of reticulocytes in circulation. Reticulocyte counts in cats may show a "false" increase due to elevated epinephrine levels if the cat struggles during the blood draw; however, the aggregate reticulocyte count can be a fairly good indicator of the degree of bone marrow response to anemia when considered in conjunction with the hematocrit. Blood smear analysis allows identification of RBC morphologic abnormalities (e.g., Heinz bodies) and other indicators of oxidant damage, autoagglutination, methemoglobinemia, or blood parasites.
Bone Marrow Evaluation
If the anemia appears to be nonregenerative based on the CBC and the lack of reticulocytes after at least 4 to 7 days of anemia, and the etiology of the anemia is not apparent based on an initial minimum database, then evaluation of the bone marrow is warranted.
Bone marrow aspiration allows for examination of the activity of the erythroid, myeloid, and megakaryocyte series and can help to identify neoplastic cells or infectious organisms. Bone marrow cytology can aid in the diagnosis of primary bone marrow disorders such as erythroid hypoplasia, pure red cell aplasia, myelodysplastic syndromes (MDS), aplastic anemia, and leukemia.
A peripheral nonregenerative anemia may be accompanied by erythroid hypoplasia and relative myeloid hyperplasia in the bone marrow. Bone marrow examination for iron stores using Prussian blue or other staining may be helpful in ruling out iron deficiency as the cause of anemia. Healthy cats typically do not have visible iron stores in their bone marrow, so the absence of these stores is not diagnostic. However, if iron deposits are identified in the marrow, iron deficiency can be excluded. Cats with anemia of inflammatory disease may have normal to increased bone marrow iron stores because macrophages of the bone marrow tend to sequester iron.
If bone marrow aspiration yields a poorly cellular or nondiagnostic sample, a core biopsy may be beneficial. A core biopsy allows for improved evaluation of bone marrow cellularity, iron stores, and bone marrow stroma. This may be particularly helpful in the diagnosis of conditions that alter the stroma of the bone marrow, such as myelofibrosis. A current CBC should always be reviewed in conjunction with bone marrow evaluation.
Serum Iron Evaluation
Laboratory findings for cats with iron-deficiency anemia can closely resemble those for patients with anemia of inflammatory disease. An iron panel, which is used to evaluate iron levels and availability, can aid in making the distinction between these conditions. Because processes other than iron deficiency can decrease iron values, a serum iron level is a nonspecific measurement. Total iron-binding capacity (TIBC) is a measure of serum transferrin content relative to iron content. The TIBC in a healthy cat is between 169 and 325 µg/dL. The difference between serum iron levels and the TIBC indicates the unsaturated iron-binding capacity, or the amount of iron-binding capacity still remaining on transferrin. The normal unsaturated iron-binding capacity for cats is 105 to 205 µg/dL. The percentage of transferrin saturation can be calculated by dividing the serum iron value by the TIBC value.
With iron deficiency, the TIBC is generally increased, while serum ferritin levels tend to be decreased. However, in addition to being an iron-binding protein, ferritin is also an acute-phase inflammatory protein. Thus, ferritin levels may be increased in conditions involving an inflammatory response, particularly in interleukin-1 production.
Currently, there is no established threshold hematocrit below which a cat requires a blood transfusion. Rather, the decision to transfuse an anemic patient is based on the hematocrit in conjunction with the clinical picture. Clinical signs such as tachycardia, tachypnea, poor pulse quality, lethargy, weakness, or pale mucous membranes may indicate that a transfusion is warranted. Cats are most often transfused because of anemia as a result of blood loss, followed by erythropoietic failure (most commonly due to renal failure).
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