Anemia: laboratory investigation

Introduction

• Anemia is a symptom of disease NOT a diagnosis.
• Identification of anemia on a blood screen demands further investigation to characterize the type and establish the etiology of the anemia.

Is the patient anemic?

• Anemia is an absolute decrease, of more than 2 standard deviations below the normal mean at normal blood volume, in at least one of:
  • Hemoglobin concentration    .
  • Packed cell volume (PCV)    .
  • Erythrocyte count (RBC count)    .
    PCV may be normal or increased in dehydrated animals with anemia.
• Once the cat is hydrated hematological parameters should be reassessed.
• Normal hematological parameters may be present in animals with acute hemorrhage in the first 24-36 hours, ie animals become hypovolemic but lose all constituents of blood in equal quantities.
• Volume support should be given and PCV monitored at regular intervals to establish severity of anemia, and response.
• The spleen may falsely elevate or reduce the degree of anemia:
  • Contraction   →   rapid bolus of stored RBC released.
  • Relaxation   →   splenic storage of RBC, removing them from circulation (rare).

Signalment

• Age - young :
  • Young kittens have lower PCVs than adults.
  • Severe parasite infestations, eg fleas or ticks, may cause significant blood loss.
  • Hemorrhage as a result of severe congenital coagulopathies    .
  • FeLV    associated.
  • Hyperlipidemia    .
• Adult :
  • Acquired coagulopathies    .
  • Immune-mediated hemolytic anemias    .
  • Late manifestation of congenital bleeding disorders (rare).
  • FeLV    associated.
  • FIA    .
• Geriatric :
  • May be prone to anemia of chronic disease, eg related to chronic renal failure    or neoplasia.
  • Neoplasia becomes increasingly likely with age.
  • Internal hemorrhage from abdominal tumors.

Clinical signs

• Weakness.
• Lethargy/inappetance/anorexia.
• Secondary signs associated with primary cause of anemia, eg FeLV or renal failure.
• Fever with FIA.
• Evidence of hemorrhage.
• Discolored urine (hematuria    , hemoglobinuria).
• Disease may be subclinical.

Clinical examination

• Pale mucous membranes.
• Tachycardia.
• Bounding pulse.
• Heart murmur.

Sources

Publications

Refereed papers

• Recent references from PubMed .

Other sources of information

• Harvey J W (2000) Microcytic anemias. In: Schalm's Veterinary Hematology . 5th edn. Lippincott, Williams & Wilkins, Philadelphia. pp 200-204.
• Mills J (2000) Anaemia. In: Manual of Canine and Feline Haematology and Transfusion Medicine. 1st edn. May M J, Mackin A & Littlewood J D (eds), BSAVA Publiscations, Gloucester, pp 29-42.