Anemia, Thrombocytes, and Blood Parasites

Clinical Pathology

Autoimmune Hemolytic Anemia (AIHA)

• Antibodies directed against RBC membrane antigens and Ab- coated RBC’s are removed from circulation.

• Hemolytic process results in varying degrees of anemia depending on antibody type, speed of development, and duration of the disease process.

• Female dogs are more commonly affected than males.

• Certain breed predispositions include: Poodles, Cocker Spaniels, Terriers, Old English Sheepdogs, Lhasa Apsos, and Shih Tzus.

• Rare in cats, usually associated with FeLv or Hemobartonella.

AIHA continued

• The spleen is the primary site for removal of RBC’s coated with IgG while the liver removes RBC’s coated with IgM.

• Onset of anemia may be acute or gradual.• Complications:

• DIC• Pulmonary Thromboembolism

Causes of AIHA

• Primary AIHA: autoantibodies directed against RBC’s with no underlying disorder, most common.

• May occur in association with immune mediated thrombocytopenia.

• Secondary AIHA: Ab production initiated by drugs, vaccines, infectious diseases and neoplastic disorders.

Diagnosis

• History and Physical Exam• CBC

• Regeneration• Spherocytes• Autoagglutination• Anemia (PCV<20%)

• Coombs Test• Splenomegaly and Hepatomegaly seen on

radiographs.

Therapy for AIHA

• Corticosteriods:• Reduces clearance of Ab coated RBC’s by

inhibiting function of macrophages in the spleen and liver.

• Prednisone at dose of 2 mg/kg/day divided BID.

• Blood transfusions in life-threatening situations.• Other immunosuppressive drugs

• Cyclophosamide• Azathioprine• Cyclosporine

• Splenectomy• Indicated if anemia is nonresponsive to

immunosuppressive drugs.

Classification of Nonregenerative Anemia

• Primary failure of erythropoiesis• Secondary failure of erythropoiesis• Nuclear maturation defects• Hemoglobin synthesis defects• Aplastic anemia• Marrow infiltration

Primary Failure of Erythropoiesis

• Patient stops producing red blood cells• Circulating blood has few reticulocytes,

normocytic, normochromatic RBC’s.• Bone marrow normal except for hypoplasia

of erythroblasts.• May be immune-related or caused by

certain drugs or neoplasia.

Secondary Failure of Erythropoiesis

• Caused by a chronic disorder such as renal failure, liver disease, inflammatory disease, neoplasia, and endocrine disorders.

• Bone marrow is normal or has slight erythroid hypoplasia.

Nuclear Maturation Defects

• Associated with folate and B12 deficiency (rare).

• Macrocytic, normochromic anemia due to a defect in DNA synthesis.

• Megablastic erythroblasts in bone marrow.• Check serum folate and supplementation

is the cure.

Hemoglobin Synthesis Defect

• Primary associated with iron deficiency.• Microcytic, hypochromic anemia due to decrease Hb

production in individual cells.• Iron deficiency can result from a poor diet, poor

absorption, and following an incident of marked blood loss.

Aplastic Anemia

• Bone marrow failure due to marrow necrosis and/or inflammation.

• Bone marrow is acellular or hypocellular resulting in anemia, thrombocytopenia, and leukopenia.

• Causes:• Ehrlichia canis• FeLv• Parvovirus• Estrogen• Phenylbutazone• Radiation• Chemotherapy

Marrow Infiltration

• Neoplasia: crowding of marrow elements with neoplastic cells.

• Myelofibrosis: hypoplasia of marrow elements with replacement by collagen (sequel to damaged marrow).

• Osteopetrosis: inherited disorder with increased bone density.

Thrombocyte = Platelets

• Platelets are produced by fragmentation of megakaryocytes in bone marrow

• 150-200 platelets are formed from one megakaryocyte.

• Lifespan: 7-10 days• Normal count: 200,000 – 500,000/mm3

• Thrombocytopenia- most common cause of bleeding in dogs.

• Normal hemostatis depends on adequate platelet number and function

• Important role in primary hemostatis involving interaction between injured blood vessel wall and platelets

When Thrombocytopenia is found

• Make sure you had a good stick, if not recollect sample from a large peripheral vein.

• If yes, perform coagulation test, CBC, tick panel.• If those are normal, then check bone marrow

Immune Mediated Thrombocytocenia

• Most common in middle-aged female dogs, less common in cats.

• May be primary cause similar to AIHA.• Secondary causes are drugs, viruses,

immune complexed, infectious disease, etc.

Coagulopathy

• Test platelets• Platelet count• Bleeding time

• Test Coagulation Factors• Activated Clotting Time (ACT)• Activated Partial Thromboplastin Time

(PTT)• Prothrombin Time (PT)

Disorders of Blood Coagulation Factors

• Von Willebrand disease (vWD): factor VIII decreased. • An additional portion of the molecule which is

important in platelet function is decreased or absent.

• Abnormal platelet function.• Increased mucosal surface bleeding time.• Excessive surgical bleeding.• Chronic, low grade bleeding possible.• PTT may be mildly prolonged• Antigen test

Buccal Mucosal Bleeding Time

• Normal clotting time 2-4 minutes• Platelet dysfunction at 10-12 minutes• Begin timing immediately after making cut.

Wound should not be wiped or disturbed until it has clotted.

Cuticle Bleeding Time

• Normal time is 2-8 minutes• Begin timing at the time the nail is cut.

Discrete drops of blood should fall from wound. A steady stream indicates that the wound is too far in the cuticle.

Equine Infectious Anemia (EIA)• Contagious and potentially fatal viral disease in

horses.• No vaccine or treatment exists.• Transmitted by biting insects such as horseflies

and deerflies.• Can also be transmitted by dirty needles.• Also called Swamp Fever• Two stages:

• Acute• Develops severe, acute signs within 2-3

weeks. Signs occur rapidly and cause only a slight increase in temperature, 30% of horses die at this stage

• Chronic• Temperature > 105˚ F

Clinical Signs of EIA

• Petechial hemorrhage• Depression• Weight loss• Edema in legs and abdomen• Anemia

Coggins Test

• Checks for antibodies to the virus

• Positive Test Options• 1. Retest• 2. Euthanize• 3. Sale for immediate

slaughter• 4. Lifetime Quarantine

Texas Law and Reactors

• Retest in 30 days at TVMDL• Official reactors are permanently marked

by using a National Uniforms Code branded on the left shoulder or neck.

• Quarantine should be at least 200 years from other equine

• All exposed equines must be tested

Common Blood Parasites you should know

• Ehrlichia platys• Brown dog tick transmits

• Erhlichia canis• Common in TX• Transmitted by Brown dog tick• 3 stages of disease

• (acute, subclinical, and chronic)• Hemobartonella felis

• FIA (feline infectious anemia)• Rickettsial organism• Transmitted by fleas, ticks, blood transfusions, queen to kitten.

• Hemobartonella canis• Rarely seen in dogs

• Cytauxzoon felis• Fatal disease characterized by anemia• Thought to be transmitted by ticks

• Anaplasma marginale• Rickettsial organism• Transmitted mechanically through equipment

• Babesia bigemina• Reportable in cattle• Texas fever, Redwater fever, Cattle tick fever

• Babesia canis• Babesia Gibsoni