2 Equine Clinical Chemistry & Hematology

Equine Clinical Chemistry and Hematology Objectives

• Enrolled students will learn about common clinical pathology tests for equine patients.
• Students will learn to interpret clinical chemistry and hematology test results in equine medicine.
• Students will understand the diagnostic value of specific tests.
• Students will understand the tests' role in treating equine patients.
• Gain insight into a patient's severity and prognosis.
• Learn effective client communication regarding diagnostic testing importance and value for equine patients.

Clinical Chemistry and Hematology Tests

• Proteins
• Enzymes
• Additional analytes
• Electrolytes
• Complete Blood Count
• Erythrocytes
• Platelets.

Protein: Albumin

• The reference interval is 3.0-4.1 g/dL.
• Albumin is an important contributor to oncotic pressure.
• Albumin is a transport protein for proteins, amino acids, hormones, and drugs.
• Albumin loss can occur via the gut or kidneys.
• Albumin synthesis can occur.
• Albumin levels can increase with dehydration.

Protein: Globulins and T.P.

• Globulins have a reference inteval of 2.7-4.0 g/dL
• Globulin elevation is associated with chronic inflammation.
  • Can be polyclonal or monoclonal gammopathy
• Fibrinogen and Immunoglobulins are types of globulins.
• Total serum protein has a reference interval of 6.1-7.4 g/dL.
• Total serum protein is composed of albumin and globulins.

Serum Amyloid A (SAA)

• SAA is an acute phase protein.
• SAA has a rapid response when there is inflammation, up to 100x.
• SAA elevations can be seen in infection with pneumonia or peritonitis.
• SAA is elevated during inflammation and vaccination, for approximately 10 days.

Alkaline Phosphatase (ALP)

• ALP's reference interval is 72-220 U/L. -ALP has isoenzymes in the liver gut, bone, and placenta.
• ALP can be induced.

Aspartate Aminotransferase (AST)

• AST's reference interval is 199-413 U/L.
• AST is found in the liver and muscle.
• AST has a longer half-life than creatine kinase (CK).

Alanine Aminotransferase (ALT)

• ALT has very low values in horses.
• ALT is not commonly reported and not on equine chemistry panels.

Creatine (Phospho) Kinase (CPK / CK)

• CPK/CK's reference interval is 93-348 U/L.
• CPK/CK has isoenzymes in the muscle, heart, and brain.
• Levels increase mildly with minimal trauma.
• Levels increase significantly with exertional rhabdomyolysis.

Gamma-Glutamyltransferase (GGT)

• GGT's reference interval is 8-33 U/L.
• GGT is a tubular enzyme.
• GGT is highly specific for liver disease in horses.
  • This includes biliary hyperplasia.
• GGT increases with cholestasis and secondarily increases with hepatocellular disease.
• Urine GGT is excreted, therefore won't change in circulation with renal disease.

Sorbitol Dehydrogenase (SDH)

• SDH's reference interval is 1 to 8 U/L.
• SDH is a hepatocellular cytosol enzyme.
• SDH has a short half-life
  • This is approximately hours.
• Continued elevation suggests ongoing hepatocellular damage.
• Increased serum activity indicates acute hepatocellular damage.
  • This is due to injury or necrosis.
• This can be caused by GIT disease, ascending insult or challenges from portal circulation, and colonic displacement.
• SDH is generally a mild to moderate increase when there are changes in liver enzymes and displacement is present for one to a few days.

Anion Gap

• The reference interval is 0 to 9.
• It represents the serum cations minus the anions.
• AG = [(Na+ + K+) – (Cl- + HC03-)].
• An increased AG occurs with unmeasured anions
  • This includes small organic anions, albumin, and exogenous toxins.
• Lactic acidosis and renal insufficiency increase the anion gap.
• A decreased anion gap is very rare unless there is hemodilution or hypoalbuminemia.
• Sepsis is commonly associated with lactic acidosis, which can result in an elevated anion gap.

Bile Acids

• The reference interval for Bile Acids is 0-20 µmol/L.
• It measures liver function.
• Bile acids are cholesterol metabolites recycles from the liver to GIT with reabsorption in the ileum.
• Bile Acids is evaluated in combination with bilirubin, hepatic enzyme and overall hepatic function.
  • Bile acids increase with impaired hepatic function.

Bilirubin

• The reference interval is:
  • Total: 0.0-3.2 mg/dL -Direct: conjugated = 0.0-0.4 mg/dL
  • Indirect: unconjugated calculation < 2.8 mg/dL
• Bilirubin is a product of hemoglobin metabolism from RBCs and non-heme porphyrins.
• Increased direct acting occurs with hepatic obstruction (intrahepatic or extrahepatic cholestasis).
• Increased indirect acting (unconjugated) results from hemolysis and fasting hyperbilirubinemia in horses.
  • Fasting hyperbilirubinemia in horses may be as high as 12 mg/dl
  • Indirect acting is unconjugated

Calcium

• The reference interval is 10.2-13.4 mg/dL.
• Calcium is protein bound, ~50%.
• Calcium is complexed.
• Free = ionized = active form.
• Hormonal and nutritional influences include parathyroid hormone, calcitonin, and vitamin D.

Hypercalcemia/Hypocalcemia

• Causes of hypercalcemia:
  • Renal disease (chronic)
  • Neoplasia = paraneoplastic disease
  • Hyperparathyroidism
• Causes of hypocalcemia:
  • GI disease/anorexia
  • Hypoalbuminemia
  • Cantharidin toxicosis
  • Lactation

Chloride

• The reference interval is 98-109 mEq/L.
• The major extracellular anion.
• Has a direct relationship with sodium.
• Has an inverse relationship with bicarbonate.
• Loss occurs with hypochloremia.
  • Proximal enteritis
  • Mechanical GI obstruction.
  • Colonic loss
  • Sweating/endurance level activity

Fluid therapy selection

• 0.9% NaCl is the fluid selection with esophageal obstruction for horses.
• Common changes includes hypochloremic metabolic alkalosis.

Creatinine

• The reference interval is 0.4-2.2 mg/dl.
• It is a non-protein nitrogenous substance from muscle metabolism.
• It is directly influenced by glomerular filtration.
• Increased creatinine levels with decreased GFR.
  • It can be Prerenal, renal, or post-renal
• It is sourced by muscle mass
  • Draft or heavily muscled horses' normal value may be in the high-normal range.

Glucose

• The reference interval is 80-110mg/dl.
• Affected by diet, insulin/glucagon, and removal from circulation.
• Hyperglycemia is affected by Pituitary Pars Intermedia Dysfunction (PPID), Glucocorticoids, and Hyperadrenocorticism.
• Hypoglycemia is affected by severe sepsis, starvation, and malabsorption.
  • Can be artifactual from in vitro glycolysis by erythrocytes.
  • A repeat test may be needed to determine if actual or artifactual.

Magnesium

• The reference interval is 1.4-2.3 mg/dl.
• Serum levels are diet dependent and affected by Intestinal absorption, renal excretion, and lactation.
• Very important cofactor -reduced by intestinal disease, sweating, and Cantharidin toxicosis
• Elevated with renal failure and maximal exercise.

Potassium

• The reference interval is 2.9-4.6 mEq/L.
• Potassium is intracellular > extracellular.
• Serum levels don’t reflect total stores.
• Consider serum pH/Body Status.

Hyperkalemia

• Can be due to Acidemia
• Renal failure
• Necrosis/marked cell death
• Insulin deficiency
• Pancreatic exhaustion
• Hyperkalemic periodic paralysis
• HYPP
• Erythrocyte hemolysis.
  • This is caused by improper handling that could result in hemolysis.

Hypokalemia

• Caused by depletion of body stores with latrogenic furosemide
• Redistribution into the intracellular stores
• Alkalemia
• Anorexia
• GI loss
• Sweating
• Urinary loss

Sodium

• The reference interval is 128-142 mEq/L.
• An extracellular space
• Bound in skeletal bone
• Balance is controlled by changes in water and aldosterone which allows absorption of kidneys.

Hypernatremia and Hyponatremia

• Hypernatremia:
  • Dehydration/salt poisoning
• Hyponatremia:
  • Diarrhea/Sweating -Sequestration of fluid and renal disease

Bicarbonate

• The reference interval is 20-24 mEq/L.
• The major portion of C02. Changes are interpreted as changes in HC03.
• Reduction indicates metabolic acidosis
  • Example - diarrhea/Renal tubular acidosis
• Increase indicates metabolic alkalosis
  • Example-esophageal obstruction/reflux

Urea Nitrogen

• The reference interval is 9-20 mg/dl.
• Nitrogen Synthesized in the liver - Following Ammonia absorption.
• Increased BUN leads to Azotemia- accumulation of nitrogenous waste in the blood.
  • Prerenal ,renal,post -renal Check-U/A >1.020 with low sodium/absence of enzymuria.
• Reduced BUN due to liver failure,starvation, anabolic steroids .

Hematologic Analysis

• Hematologic Analysis is Complete Blood Count(CBC)

Equine Hematology

• The total white blood cell count reference interval is 5.6-12.1X 10^3/μι
• Total Count
  • Neutrophils
  • Lymphocytes
  • Eosinophils
  • Monocytes
  • Basophils

Basophils

• Basophils reference interval is 0-0.3 x 10^3/μι.
• Basophils are rarely present in the circulation of healthy horses.
• Could be a sign of allergic dermatitis.

Eosinophils

• The reference interval is 0-0.7 X 10^3/μι
• Parasitic infection rarely increases peripheral eosinophils.
• Eosinophilic granulocytic leukemia has been reported but is very rare.
• Eosinopenia is hard to characterize, because eosinophil concentration is typically very low.

Lymphocytes

• The reference interval is 1.2-5.1 X 10^3/μι
• Lymphocytosis occurs because of excitement or exercise in young animals.
• Lymphopenia occurs because of:
  • Stress
  • Corticosteroid use
  • Endotoxemia
  • Bacterial infection
  • Viral Disease
  • Immunodeficiency
  • Age-primarily geriatric horses

Monocytes

• The Reference Interval is: 0-0.7 x 10^3/µl.
• Indicates Chronic Inflammation
  • Suppurative/Pneumonia
  • Granulomatous

Neutrophils

• The reference interval is 2.9-7.5 X 10^3/µl.
• Catecholamine release results in de-margination of PMNs with increases concentration in circulation.
  • Caused by stressors ,exercise,excitation ,corticosteroid surge.

Neutropenia

• Endotoxemia:results in margination in the Vascular endolthelium
• Bacterial sepsis
• Bone marrow dysfunction
  • Neoplasia

Neutrophilic Inflammation

• Acute Bacterial Infection
• Chronic localized bacterial infection
• Results -From Endotoxemia and rebound neutrophilia
• Surgery
• Neoplasia

Erythrocytes

• The reference interval is 6-10.43 X 10^3/µl
• Hematocrit is 32-43%
• Can result in Anemia: Chronic infections,Anemia with chronic infections Blood loss Hemolysis Parasitism Renal failure - reduced Erythropoietin secretion
  • Hematopoietic malignancies( rare)

Polycythemia

• Relative erythrocytosis is caused by dehydration and splenic contraction.
• Absolute erythrocytosis is caused by hypoxia (high altitude), chronic pulmonary disease, and inappropriate RBC production from hepatocellular carcinoma.

Equine Erythrocytes

• Marrow retention until maturation is Complete.
• Can be Polychromasia or Macrocytosis.
• Howell-Jolly bodies may be present in Horses.
• Rouleaux formation is common.
• Differentiate from agglutination with saline solution 1:4.

Reticulocytes

• Reference range of ZERO.
• Immature RBC
• Fine reticulum of blue staining and nucleotide material.
• Species = regeneration= Horses = stay in mature marrow.

Thrombocytes

• Ref int: 117-256 X 103/µl
• Decreased platelets are are affected by: DIC, IMT, endotoxemia, EIA, equine ehrlichiosis,lymphoma -Pseudothrombocytopenia- Clumping In EDTA -USE citrate / heparin.
• Increased Thrombocytes-Due Chronic inflammation/R.equi.

Summary

• Clinical pathology can be instrumental in case management.
• Serum chemistry and CBC tests are commonly used when evaluating equine patients.
• Serial monitoring may be indicated to determine the course of disease.
• If an unexpected result is obtained, repeat analysis is indicated.
  • Will help to rule out errors.