Disorders of the Equine Hemolymphatic System I & II

What is the normal PCV for horses?

32 to 48%

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

Increase

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

Decrease

Hemoglobin is approximately _________ of the PCV

1/3

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

Increases

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

A

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

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

T or F: Rouleaux formation is normal in horse blood

A

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

Agitate blood

Basophilic nuclear remnants in RBCs

Howell jolly bodies

This is secondary to decreased oxygen carrying capacity of the blood

Hypoxia

Oxygen content in arterial blood

CaO2

Carries the majority of oxygen throughout the body

Hemoglobin

What are the three causes for anemia?

1. Blood loss (internal or external)

2. Hemolysis (RBC destruction)

3. Impaired RBC production

Decreased RBCs and hemoglobin

Anemia

Acute anemia has (insidious or severe) clinical signs

Severe

Chronic anemia has (insidious or severe) clinical signs

Insidious

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

A

Inadequate oxygenation of tissues

Hypoxia

Decreased blood volume

Hypovolemia

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

Hypoxia, hypovolemia

What clinical signs are associated with anemia?

1. Tachycardia and tachypnea

2. Mucosal pallor

3. Icterus

4. Hemoglobinuria

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

1. Weakness

2. Colic

3. Dyspnea

4. Ataxia, blindness, collapse

How is anemia clinically diagnosed?

1. CBC and cytological evaluation

2. Agglutination vs rouleaux

3. Bone marrow evaluation

4. Myeloid:erythroid (M:E) ratio

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

A

Performed to distinguish rouleaux from agglutination

Saline test

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

Negative

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

Positive

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

Immune mediated disease

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

Coomb's test

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

Agglutination

Which site is most commonly used for bone marrow evaluation?

Sternum

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

Decreased

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

Increased

Which blood types are the most immunogenic in horses?

Qa and Aa

Donkey blood incompatible for horses

Donkey factor

Donor RBCs + recipient alloantibodies

Major cross match

Donor alloantibodies + recipient RBCs

Minor cross match

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

A

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

Qa and Aa negative gelding or maiden mare

When should you perform a blood transfusion?

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

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

Gradual/chronic

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

20 to 40%

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

A. 36%

B. 8%

How can you avoid adverse reactions to transfused RBCs?

Start slow and increase transfusion rate if no reactions

What are clinical signs of mild adverse blood transfusion reactions?

1. Mild tachycardia

2. Fever

3. Urticaria

What are clinical signs of severe adverse blood transfusion reactions?

1. Marked tachycardia, dyspnea, pyrexia

2. Colic, diarrhea

3. Anaphylaxis, shock, pulmonary edema

4. Hemolysis, DIC

What are causes for acute hemorrhage?

1. Trauma, surgery, coagulopathy

2. Guttural pouch mycosis (epistaxis)

3. Hemoabdomen, hemothorax

4. Peripartum hemorrhage (uterine artery)

Hemoperitoneum from acute hemorrhage presents with what clinical signs?

Colic and abdominal distention

Hemothorax from acute hemorrhage presents with what clinical signs?

Dyspnea and braced stance

T or F: With hemolytic anemia TP should NOT decrease

A

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

Decrease

_______________ may delay a decrease in PCV with acute hemorrhage

Splenic contraction

Blood ______________ increases secondary to tissue hypoxia

Lactate

How do you treat acute hemorrhage?

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)

What are causes for chronic blood loss?

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

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

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

A

What is considered evidence of depleted iron stores?

1. Hypochromic, microcytic anemia

2. Low serum iron

3. Decreased bone marrow iron stores

4. Increased total iron binding capacity (TIBC)

RBC destruction within vasculature resulting in hemoglobinuria and hemoglobinemia

Intravascular hemolytic anemia

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

A

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

B (can occur independent of intravascular hemolysis)

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

Extravascular

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

Extravascular hemolytic anemia

What are clinical signs of hemolytic anemia?

1. Icterus

2. Hemoglobinuria and hemoglobinemia

3. Fever, mild colic

4. Other signs of anemia secondary to hypoxia

What is the hallmark clinical sign of hemolytic anemia?

Hemoglobinemia and hemoglobinuria

What on hematologic evaluation will suggest hemolytic anemia?

1. Increased indirect or total bilirubin

2. Decreased PCV

3. Normal serum protein

4. +/- inflammatory leukogram

What are common differentials for hemolytic anemia?

1. Equine piroplasmosis (babesiosis)

2. IMHA

3. Neonatal isoerythrolysis

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

This is a reportable tick borne disease of all equids

Equine piroplasmosis

Which hemoprotozoan parasites can cause equine piroplasmosis?

1. Babesia caballi

2. Theileria equi

Babesia caballi is (smaller or larger)

Larger

Theileria equi is (smaller or larger)

Smaller

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

A. Theileria equi

B. Theileria equi

What are the DH and vector for piroplasmosis?

Ticks

What are the reservoir for piroplasmosis?

Persistently infected horses

US outbreaks of piroplasmosis are primarily due to what?

Contaminated equipment (needles, syringes, tools)

T or F: Piroplasmosis only causes extravascular hemolysis

B (also causes intravascular)

What are the three clinical presentations of piroplasmosis?

1. Peracute

2. Acute

3. Chronic

Peracute piroplasmosis is described as what?

Sudden death

Acute piroplasmosis is described as what?

1. Hemolytic anemia, icterus, high fever

2. Peripheral edema

3. Coagulopathy and SIRs

Chronic piroplasmosis is described as what?

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

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

There are silent carriers

What lab findings will suggest piroplasmosis diagnosis?

1. Anemia

2. Thrombocytopenia (+/- coagulopathy)

3. Hyperbilirubinemia (hemolysis)

What are differentials for piroplasmosis?

1. Viral: EIA, EVA

2. Bacterial: purpura, anaplasma

3. Autoimmune: IMHA

4. Toxin: red maple leaves

How do you diagnose Piroplasmosis?

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

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

cELISA

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

Supportive care

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

1. Eliminate carriers (euthanasia or quarantine for life)

2. USDA controlled program (imidocarb dipropionate)

Antibodies directed against normal RBC surface antigens

Primary IMHA

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

Secondary IMHA

(Primary or secondary) IMHA is most common

Secondary

What is included in hematologic analysis for IMHA diagnosis?

1. Consistent with hemolytic anemia

2. Bone marrow: regenerative process

3. Positive Coomb's test

4. Flow cytometry

How do you treat IMHA?

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

2. Supportive care and blood transfusion

3. Immunosuppressive medications (corticosteroids or other immunomodulators)

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

Qa and Aa

What are the three risk factors for 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

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

Neonatal isoerythrolysis

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

Donkey factor

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

1. Icterus

2. Fever

3. Weakness

How do you diagnose and prevent neonatal isoerythrolysis?

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

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

NO nursing the first 24 hours, alternate source of colostrum

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

B