Assessing Pet Health by Laboratory Testing

Background

Laboratory diagnostic tests play an important role along with a thorough physical examination and patient history in the overall evaluation of both human and animal patients.

For more than 60 years, human healthcare has benefited from detecting various chronic diseases before clinical symptoms appeared. Numerous clinical studies have identified the most useful diagnostic parameters in detecting early disease states and the effect of early intervention on disease progression. Certainly, early detection of various risk factors for chronic diseases and therapeutic intervention has significantly reduced human morbidity and mortality.

Until recently, however, veterinary medicine remained focused on the diagnosis and treatment of disease once symptoms were manifested, when an owner brings the pet in for diagnosis and treatment.  Fortunately, this paradigm has changed significantly to the extent that more dogs, cats and domestic farm animals are diagnosed with health issues before they become serious.  Further, recent studies in these species have shown the value of early intervention in greatly improving patient survival and life span.

Geriatric Animals

Wellness programs emphasizing annual or semiannual examinations, blood and urine testing and even radiography have routinely been offered by veterinarians for more than a decade for the older (senior and geriatric) pets. Results of laboratory monitoring of healthy geriatric pets, for example, showed that 20% of dogs and 17% of cats studied were found to have clinically significant disease.

The logical assumption from these findings is that earlier discovery of disease should lead to improved treatment response and longevity. The fact that chronic disease is observed more frequently in older animals is logical as the incidence of many diseases increases with age.

Young Adult Animals

While results of available studies could not predict how many of these patients will develop clinical disease or even if the abnormalities were confirmed upon further testing, ongoing monitoring of these pets should be informative. Regardless, the results document that a number of chronic diseases occur at much higher rates in dogs and cats than in humans. It is also clear that early intervention in the case of renal disease shows promise of slowing morbidity and mortality.

In 2018, results summarized by the Idexx Laboratories found abnormal laboratory results warranting further diagnostics for:

• 1 in 7 adult dogs and cats
• 1 in 5 seniors
• 2 in 5 geriatrics

Understanding Your Pet’s Blood Work

What does it mean to run a CBC on your pet?

• Complete blood count (CBC) is one of the most common blood tests used
• It analyzes the three major types of cells in the blood:
  • Red blood cells (RBC)
  • White blood cells (WBC)
  • Platelets
• In addition to counting the blood cells, the CBC:
  • Measures hemoglobin (the oxygen-carrying molecule in the red blood cells)
  • Estimates the RBC volume
  • Sorts the WBC by type, and
  • Determines platelet size (MPV= mean platelet volume)

Red Blood Cells (RBCs)

• RBC count determines the actual number of these cells in a sample of blood.
• Hemoglobin measures the total amount of this oxygen-carrying protein in the blood.
• Hematocrit (packed cell volume, PCV) measures the percentage of the blood volume that consists of RBCs.

White Blood Cells (WBCs) = Leukocytes

• WBC count includes:
  • Monocytes
  • Lymphocytes
  • Basophils
  • Eosinophils
  • Neutrophils

Neutrophils are the most abundant type of WBC

• First cell that arrives at the site of infection
• What does it mean when these are high?
  • Infection
  • Injuries
  • Acute stress
  • Inflammatory disorders

Eosinophils

• Eosinophils contain red-staining granules
• What could it mean when the eosinophil count is high?
  • Allergic reactions
  • Asthma
  • Parasitic infestation

Basophils

• Basophils, a rare type of WBC, play a role in immune surveillance and wound repair.
• Basophils can release histamine and other cell mediators, and initiate allergic reactions.
• What could it mean when the Basophils are high?
  • Inflammatory reactions, particularly those that cause allergic symptoms

Monocytes

• Monocytes fight certain infections, help other WBCs remove dead or damaged tissues, destroy cancer cells, and regulate immunity against foreign substances.
• After leaving the bloodstream they become tissue Macrophages
• What could it mean when the Monocyte count is high?
  • Chronic infections
  • Autoimmune disorders
  • Blood disorders
  • Certain cancers

Lymphocytes

• Lymphocytes act in immune defence by recognising antigens, producing antibodies, and destroying cells that could cause damage.
• There are three main types:
  • T-cells
  • B-cells
• Natural killer cells

Blood Chemistries

• These tests evaluate organ function, electrolyte status, and hormone levels
• These tests are used for:
  • Baselines as pets age
  • Pre-anesthetic evaluation
  • Evaluating sick animals
  • When on long-term medications

Amylase

• Elevations typically show pancreatitis or kidney disease
• Pancreatic inflammation, necrosis, or pancreatic duct blockage releases amylase into the blood and peritoneal cavity. This elevates serum amylase levels to several times normal.

Alkaline phosphatase (ALK P)

• Elevations may indicate:
  • Liver damage
  • Cushing’s disease (hyperactive adrenal glands)
  • Active bone growth in young pets
  • This test is especially significant in cats as even slight elevations are usually indicative of liver disease.

Alanine aminotransferase (ALT, SGPT)

• Sensitive indicator of active liver damage but does not indicate cause or reversibility of the damage.
• Increased serum activity indicates recent or ongoing liver cell damage. An increase of at least three times normal indicates significant liver damage within the previous several days.

Aspartate aminotransferase (AST, SGOT)

• Mitochondria-bound enzyme found in several body tissues but is especially high in liver and striated (striped) muscle.
• Rising levels indicate continued, severe insult to liver cells. Normal half-life of this enzyme in blood is about 12 hours in dogs and only 2 hours in cats.

Blood urea nitrogen (BUN)

• Indicates kidney function
• Increased blood level is called azotemia and may be caused by kidney, liver, heart disease, urethral blockage, shock, dehydration, or even intestinal or stomach foreign body.
• Low BUN may indicate a cirrhotic liver, or portal vascular liver shunt, but please note that pets fed raw diets normally have higher BUN levels.

Electrolytes/Minerals

• Essential for proper functioning of cells
• Should be interpreted together, along with patient’s hydration status
• Intake primarily achieved via diet
• Excretion/Regulation achieved mainly through the kidneys
• Comprehensive lab work, including minerals and electrolytes, recommended annually in veterinary patients
• Critically ill patients (those receiving fluid therapy) or patients with renal dysfunction should be monitored frequently

Calcium

• Important in specific cellular processes, particularly Muscle and Nerve cells
• Found almost exclusively in bone
• Regulated mainly by the Kidneys

Chloride

• Major negatively charged ion in the body
• Affected by both water and sodium concentration. Should always consider patient’s hydration status

Magnesium

• Important in many cellular processes
• Found mostly in bone and muscle cells
• Regulated mainly by the Kidneys

Potassium

• Vital to specialized cellular processes.
• About 70% of body potassium is found in Muscle cells
  • Regulated by the Kidneys and cellular shifts (translocation)

 Sodium

• Major positively charged ion in the body
• Linked to body water balance. Should always consider patient’s hydration status
• Regulated by the kidneys via specialized cells that retain both sodium and water

Kidneys

• BUN (see above)
• Creatinine
  • Product of normal muscle metabolism
  • Used to measure kidney filtration rate. Only the kidneys excrete this substance, and if it builds up to abnormal levels, it indicates decreased or impaired kidney function
  • This test helps distinguish between kidney and non-kidney causes of an elevated BUN
  • Low levels are sometimes seen in kidney damage, protein starvation, liver disease, or pregnancy
  • Pets on raw diets normally have higher levels

Urinalysis

• Involves checking appearance, concentration and content of urine
• Evaluates kidney function, bladder pathology, presence of infection, urine concentration, checks if bladder stones or their precursor crystals are present, and other diseases.

 Urine Specific Gravity (SG)

• Used to determine whether urine concentrating ability is adequate

High SG

• Dehydration
• High levels of glucose or protein

Low SG

• Dilute urine
• Renal failure

pH

• Urine pH is typically acidic in dogs and cats, and alkaline in horses and ruminants, but varies depending on diet, medications, or presence of disease.
• Urine pH will affect crystalluria because some crystals, such as struvite, form in alkaline urine, whereas other crystals, such as cystine, form in acidic urine.

Protein

Urine Protein: Creatinine Ratio

• Measure of kidney failure

 Urine Cortisol: Creatinine Ratio

• Measure of adrenal gland cortisol output
• Urine must be collected at home before the pet exercises in the morning

Herbs that support the kidneys

• Rehmannia
• Vitamin B Complex
• Bromelain = enzyme from pineapple, reduces inflammation
• Chinese Rhubarb (Rheum officinale)

References

Antech Diagnostics News (2001). Laboratory data in geriatric dogs & cats. April 2001

Antech Diagnostics Monograph (2008). An analysis of canine and feline wellness profiles in young adults: the case for early detection of chronic disease.

Idexx Laboratories. Graphic chart.  JAVMA, 253 (10):1203, 2018.