Disorders of the Equine Hemolymphatic System I & II

32 to 48%

What is the normal PCV for horses?

Increase

Excitement/pain may result in a transient (decrease or increase) in PCV

Decrease

Sedation with alpha-2 agonists may result in transient (decrease or increase) in PCV

1/3

Hemoglobin is approximately _________ of the PCV

Increases

The hemoglobin RBC indice (decreases or increases) with intravascular hemolysis

A

T or F: Peripheral reticulocytes in equine blood are extremely rare

1. Increases in RBC parameters (MCV, MCHC, RDW)

2. Signs of anisocytosis on smear

3. Increased reticulocytes and a myeloid:erythroid ratio < 1.0 on bone marrow analysis

Other than the presence of reticulocytes, what other parameters are used to determine if regeneration is present?

A

T or F: Rouleaux formation is normal in horse blood

Agitate blood

Rouleaux formation predisposes RBCs to sedimentation, for this reason you should to what before analysis?

Howell jolly bodies

Basophilic nuclear remnants in RBCs

Hypoxia

This is secondary to decreased oxygen carrying capacity of the blood

CaO2

Oxygen content in arterial blood

Hemoglobin

Carries the majority of oxygen throughout the body

1. Blood loss (internal or external)

2. Hemolysis (RBC destruction)

3. Impaired RBC production

What are the three causes for anemia?

Anemia

Decreased RBCs and hemoglobin

Severe

Acute anemia has (insidious or severe) clinical signs

Insidious

Chronic anemia has (insidious or severe) clinical signs

A

T or F: Chronic anemia may be subclinical until HCT < 15%

Hypoxia

Inadequate oxygenation of tissues

Hypovolemia

Decreased blood volume

Hypoxia, hypovolemia

Anemia manifests through clinical signs associated with ____________ and sometimes _____________ depending on cause, whether acute or chronic, and severity

1. Tachycardia and tachypnea

2. Mucosal pallor

3. Icterus

4. Hemoglobinuria

What clinical signs are associated with anemia?

1. Weakness

2. Colic

3. Dyspnea

4. Ataxia, blindness, collapse

What are clinical signs of anemia that are severe and warrant an immediate blood transfusion?

1. CBC and cytological evaluation

2. Agglutination vs rouleaux

3. Bone marrow evaluation

4. Myeloid:erythroid (M:E) ratio

How is anemia clinically diagnosed?

A

T or F: Auto-agglutination is NOT a normal occurrence in horse blood

Saline test

Performed to distinguish rouleaux from agglutination

Negative

If you perform a saline test and the rouleaux disperse, this is a (negative or positive) result

Positive

If you perform a saline test and the agglutination will not disperse, this is a (negative or positive) result

Immune mediated disease

A positive result on a saline test is indicative of what?

Coomb's test

Blood test used to evaluate for immune mediated hemolytic anemia (IMHA)

Agglutination

A positive test for the Coomb's test means there is _________________

Sternum

Which site is most commonly used for bone marrow evaluation?

Decreased

A(n) (decreased or increased) M:E ratio is considered a regenerative response

Increased

A(n) (decreased or increased) M:E ratio is considered a non-regenerative response

Qa and Aa

Which blood types are the most immunogenic in horses?

Donkey factor

Donkey blood incompatible for horses

Major cross match

Donor RBCs + recipient alloantibodies

Minor cross match

Donor alloantibodies + recipient RBCs

A

T or F: Most horses can tolerate an unmatched transfusion if they have never had a prior transfusion

Qa and Aa negative gelding or maiden mare

If cross match is not possible, you should choose what type of donor?

1. PCV <12%

2. Horse clinically unstable (dyspnea, HR > 60 BPM, ataxia, weakness, collapse)

3. Loss of 30 to 40% of blood volume (acutely or ongoing loss during hemorrhage)

4. Severe hemolysis, methemaglobinemia

When should you perform a blood transfusion?

Gradual/chronic

Most horses are usually okay with a PCV ≥ 12% and Hb > 7 g/dL if the onset of anemia or blood loss has been _______________

20 to 40%

When performing a blood transfusion, you should aim to replace ____________ of total blood loss

A. 36%

B. 8%

When calculating how much blood for a transfusion, (A) normal PCV = _____________ and (B) blood volume is _________ of body weight

Start slow and increase transfusion rate if no reactions

How can you avoid adverse reactions to transfused RBCs?

1. Mild tachycardia

2. Fever

3. Urticaria

What are clinical signs of mild adverse blood transfusion reactions?

1. Marked tachycardia, dyspnea, pyrexia

2. Colic, diarrhea

3. Anaphylaxis, shock, pulmonary edema

4. Hemolysis, DIC

What are clinical signs of severe adverse blood transfusion reactions?

1. Trauma, surgery, coagulopathy

2. Guttural pouch mycosis (epistaxis)

3. Hemoabdomen, hemothorax

4. Peripartum hemorrhage (uterine artery)

What are causes for acute hemorrhage?

Colic and abdominal distention

Hemoperitoneum from acute hemorrhage presents with what clinical signs?

Dyspnea and braced stance

Hemothorax from acute hemorrhage presents with what clinical signs?

A

T or F: With hemolytic anemia TP should NOT decrease

Decrease

For acute hemorrhage due to blood loss, both PCV and TP should ____________

Splenic contraction

_______________ may delay a decrease in PCV with acute hemorrhage

Lactate

Blood ______________ increases secondary to tissue hypoxia

1. Stop the hemorrhage and address hypovolemic shock

2. Judicious use of sedation

3. Whole blood transfusion

4. Avoid removal of hemorrhage into body cavity if able (~60% of erythrocytes auto-transfused within 24 to 72 hours)

How do you treat acute hemorrhage?

1. GI or urogenital/renal disease (neoplasia, EGUS, RDC)

2. Hemostatic dysfunction (vasculitis, thrombocytopenia, coagulation factors)

What are causes for chronic blood loss?

A

T or F: Physiologic adaptation to gradual onset of tissue hypoxia secondary to anemia can delay clinical signs

1. Hypochromic, microcytic anemia

2. Low serum iron

3. Decreased bone marrow iron stores

4. Increased total iron binding capacity (TIBC)

What is considered evidence of depleted iron stores?

Intravascular hemolytic anemia

RBC destruction within vasculature resulting in hemoglobinuria and hemoglobinemia

A

T or F: Intravascular hemolytic anemia is ALWAYS accompanied by extravascular hemolysis

B (can occur independent of intravascular hemolysis)

T or F: Extravascular hemolytic anemia is ALWAYS accompanied by intravascular hemolysis

Extravascular

(Intravascular or extravascular) hemolytic anemia is most common in horses

Extravascular hemolytic anemia

RBCs phagocytized by macrophages in spleen, liver, and bone with no evidence of hemoglobinuria or hemoglobinemia

1. Icterus

2. Hemoglobinuria and hemoglobinemia

3. Fever, mild colic

4. Other signs of anemia secondary to hypoxia

What are clinical signs of hemolytic anemia?

Hemoglobinemia and hemoglobinuria

What is the hallmark clinical sign of hemolytic anemia?

1. Increased indirect or total bilirubin

2. Decreased PCV

3. Normal serum protein

4. +/- inflammatory leukogram

What on hematologic evaluation will suggest hemolytic anemia?

1. Equine piroplasmosis (babesiosis)

2. IMHA

3. Neonatal isoerythrolysis

4. Oxidative injury (heinz body anemia --> red maple toxicity)

What are common differentials for hemolytic anemia?

Equine piroplasmosis

This is a reportable tick borne disease of all equids

1. Babesia caballi

2. Theileria equi

Which hemoprotozoan parasites can cause equine piroplasmosis?

Larger

Babesia caballi is (smaller or larger)

Smaller

Theileria equi is (smaller or larger)

A. Theileria equi

B. Theileria equi

Which is (A) more prevalent and (B) causes more severe disease? Babesia caballi or Theileria equi

Ticks

What are the DH and vector for piroplasmosis?

Persistently infected horses

What are the reservoir for piroplasmosis?

Contaminated equipment (needles, syringes, tools)

US outbreaks of piroplasmosis are primarily due to what?

B (also causes intravascular)

T or F: Piroplasmosis only causes extravascular hemolysis

1. Peracute

2. Acute

3. Chronic

What are the three clinical presentations of piroplasmosis?

Sudden death

Peracute piroplasmosis is described as what?

1. Hemolytic anemia, icterus, high fever

2. Peripheral edema

3. Coagulopathy and SIRs

Acute piroplasmosis is described as what?

Nonspecific to vague or absent clinical signs (mild anemia, poor performance, lethargy)

Chronic piroplasmosis is described as what?

There are silent carriers

Chronic piroplasmosis is a problem for control of piroplasmosis, why?

1. Anemia

2. Thrombocytopenia (+/- coagulopathy)

3. Hyperbilirubinemia (hemolysis)

What lab findings will suggest piroplasmosis diagnosis?

1. Viral: EIA, EVA

2. Bacterial: purpura, anaplasma

3. Autoimmune: IMHA

4. Toxin: red maple leaves

What are differentials for piroplasmosis?

Serology (could identify parasite in RBC, but only the acute stage)

How do you diagnose Piroplasmosis?

cELISA

Which serology test is best to detect carriers? cELISA or complement fixation test

Supportive care

In endemic regions (not the US) what is the treatment for piroplasmosis?

1. Eliminate carriers (euthanasia or quarantine for life)

2. USDA controlled program (imidocarb dipropionate)

In non endemic regions (the US) what is the treatment for piroplasmosis?

Primary IMHA

Antibodies directed against normal RBC surface antigens

Secondary IMHA

Altered RBC membrane due to viral, bacterial, neoplastic, idiopathic or drug/vaccination causes

Secondary

(Primary or secondary) IMHA is most common

1. Consistent with hemolytic anemia

2. Bone marrow: regenerative process

3. Positive Coomb's test

4. Flow cytometry

What is included in hematologic analysis for IMHA diagnosis?

1. Identify and remove cause (exogenous compounds, disease)

2. Supportive care and blood transfusion

3. Immunosuppressive medications (corticosteroids or other immunomodulators)

How do you treat IMHA?

Qa and Aa

RBC factors _________________ are most commonly involved in horses in relation to neonatal isoerythrolysis

1. Mare Qa and Aa negative

2. Sire and foal Qa and Aa positive

3. Mare sensitized by previous exposure to Qa and Aa factors

What are the three risk factors for neonatal isoerythrolysis?

Neonatal isoerythrolysis

Reaction of alloantibody from the dam against the RBC antigens of the foal

Donkey factor

Virtually all mule pregnancies are incompatible for a red cell factor called ________________, which has been associated with neonatal isoerythrolysis

1. Icterus

2. Fever

3. Weakness

What are clinical signs of neonatal isoerythrolysis in 2 to 3 day old foals?

1. Blood type mare and sire

2. Minor cross match (mare serum with foal blood)

3. Jaundiced foal agglutination test (colostrum with foal blood) BEFORE foal nurses

3. Coomb's test

How do you diagnose and prevent neonatal isoerythrolysis?

NO nursing the first 24 hours, alternate source of colostrum

If a foal has a high risk of neonatal isoerythrolysis, what should you do?

B

T or F: If there is failure of passive transfer, neonatal isoerythrolysis can still occur