As an example, consider a reticulocyte % of 5. Five % reticulocytes in a dog with a PCV of 20% is twice as many reticulocytes as 5% reticulocytes in a dog with a PCV of 10%. There are 2 ways to correct the reticuloycte % for the degree of anemia, as follows:

1. Corrected retic. % =
   
   

   reticulocyte % x

   (patient PCV%) 40

   
   A corrected reticulocyte % of < 1% indicates a non-regenerative anemia. The higher the corrected value, the stronger the regenerative response.
   
2. Absolute reticulocyte number = reticulocyte % x RBC count
   
   An absolute reticulocyte count of <60,000 cells/µl indicates a non-regenerative anemia. The higher the reticulocyte count, the stronger the regenerative response.
   
   These 2 methods do exactly the same thing (correct for the effect of anemia) and give the same interpretation.
   
   The reticulocyte production index, which is a modification of the corrected reticulocyte %, is not an essential value and its validity has been questioned.

1. Hemorrhage
   
   1. Peracute (over minutes to hours) and acute (over hours to days) blood loss will initially be non-regenerative. Development of a full regenerative response takes 5–7 days after the onset of anemia.
      
   2. Chronic blood loss anemia may become non-regenerative and microcytic due to iron deficiency.
      
   3. Hemorrhage may be due to a coagulopathy or to some local disease (eg, tumor, ulcer, trauma).
      
   4. Hemorrhage is often occult, such that the lack of visible bleeding cannot be used to exclude it as a cause for anemia.
   
   
2. Hemolysis (decreased RBC lifespan)
   
   1. May occur intra- or extra-vascularly, and may be due to intrinsic red cell abnormalities (such as pyruvate kinase or phosphofructokinase deficiencies) or disorders outside the red cell (AIHA, zinc or onion toxicoses, hypophosphatemia, snake envenomation, and DIC).
      
   2. Acute hemolytic anemia may be non-regenerative. Development of a full regenerative response takes 5–7 days after the onset of anemia.
      
   3. Immune-mediated hemolytic anemia also can be non-regenerative, if it involves attack of bone marrow precursors.
      
   4. Patient signalment, or client report of pigmenturia, orange stool, or toxin exposure (onion, zinc) can increase the clinical index of suspicion for hemolysis. Laboratory abnormalities that support hemolysis as a cause of anemia include: presence of marked regenerative anemia along with a normal total protein, hyperbilirubinemia, abnormal bilirubinuria, hemoglobinemia, hemoglobinuria, red cell autoagglutination, presence of Heinz bodies or numerous spherocytes.

Indications for bone marrow evaluation include non-regenerative anemias without apparent cause, presence of pancytopenia or anemia and neutropenia, and reports of "blasts" or atypical cells on peripheral blood smear review.

1. Anemia of chronic disease
   
2. Renal failure
   
3. Endocrinopathies
   
   1. Addison’s disease
      
   2. Hypothyroidism
      
4. AIHA with bone marrow involvement (maturation arrest or red cell hypoplasia).
   
5. Bone marrow disease such as myelodysplasia, hematopoietic neoplasia, myelophthisis (crowding out of marrow by cancer cells), aplastic anemia (phenylbutazone, estrogen, phenobarbital, radiation), ehrlichiosis, and systemic mycoses.
   
6. Nutritional
   
   1. Iron deficiency
      
   2. Folic acid deficiency (seen occasionally in severe intestinal disease)
      
   3. Protein-calorie malnutrition
      
7. Early hemorrhage or hemolysis