Pre-Anesthetic Blood Testing

 

Why do we check it?

  • To monitor any pre existing conditions
    • Examples:  Chronic kidney failure, liver disease
  • To detect any unknown underlying diseases
    • Examples:  Anemia, infection, kidney disease, liver disease
  • Anesthesia and the drugs involved affect the body in several ways
    • It causes a decrease in blood pressure, which can in turn negatively affect kidneys that are already damaged.
    • Many of the drugs used are metabolized or excreted by the liver or kidneys.  If either of these organs are not working properly, the drugs can build up to dangerous levels in the system.
    • If we are aware of any underlying problems, we can postpone an elective procedure (spay, neuter, dental) until the problem has been further investigated or corrected, or, we can modify our anesthetic protocol to try and minimize the potential for negative effects.

 

What are we checking?

            Liver values

·        Alanine Aminotransferase (ALT):  Liver specific enzyme, released into the blood anytime there is damage to liver cells.

·        Alkaline Phosphatase (SAP, ALKP):  This enzyme is also used to evaluate the liver.  It can be released into the blood if there is damage to liver cells, or more specifically, if there is a problem in the bile duct system or the liver.  This enzyme is also affected by other factors, such as certain drugs (corticosteroids, Phenobarbital), bone disease or growth, and endocrine diseases (hypo/hyperthyroidism, Cushing’s disease, Diabetes).

·        Total Bilirubin (TBIL):  Bilirubin is formed in the liver as a by-product of red blood cells.  TBIL may be increased in the blood for two main reasons;

o       Hemolytic disease (rupture of red blood cells):  red blood cells are being destroyed faster than normal.

o       Heptobiliary disease:  liver failure or bile duct obstruction.

Kidney Values

·        Blood Urea Nitrogen (BUN):  BUN is a waste product (from broken down proteins) this is normally excreted by the kidneys.  Its value can be affected by several different factors.

1.      Pre-renal:  Dehydration, high protein meals or GI hemorrhage may cause an increase in BUN.  Sever liver disease, portosystemic shunts, or starvation may cause a decreased BUN.  This is determined by looking at the clinical signs, the other blood values and a urinalysis.

2.      Renal:  Kidney failure (chronic or acute), kidney infection.  This is also determined by looking at clinical signs, other blood values and a urinalysis.

3.      Post-renal:  Urinary Obstruction.  This is usually pretty obvious by clinical signs, and can lead to kidney failure.

·        Creatinine (Crea):  Crea is a by-product of muscle breakdown which is excreted in the urine.  Unlike BUN, it is not as affected by the pre-renal factors, and is a good indicator of kidney disease.  It is elevated if the kidneys are not working properly, although it can be falsely decreased in animals that are severely muscle wasted.

Calcium and Phosphorous

·        Calcium (Ca):  Ca can be affected by many different diseases.  The most common causes for an increase include cancer and kidney failure.  Others are rat poisoning, young dogs, dehydration, primary, or unknown in cats.  Decreases can be caused by kidney failure, low protein levels, intestinal malabsorption, or nutritional. 

·        Phosphorous (Phos):  The most common causes for increased Phos include kidney failure, young growing animals, and urinary obstruction.  A decrease in Phos can be due to decreased intake, decreased absorption, vomiting, primary hyperparathyroidism, and hypercalcemia of malignancy.

Proteins

·        Albumin (ALB):  ALB is created in the liver.  It is increased in the blood if an animal is dehydrated.  Levels can be decreased in liver disease (decreased production), starvation, maldigestion, malabsorption, loss through kidneys in certain diseases, loss through the GI tract with certain diseases, loss of blood, or over-hydration.

·        Total Protein (TP):  The TP value includes ALB and other large proteins.  This value is also affected by hydration status, liver, GI, and kidney disease, also chronic infection or inflammation. 

Other Values

·        Glucose (Glu):  Glucose will be elevated in diabetic animals and stressed cats (slight).  Decreased glucose can be seen in small puppies and kittens that are malnourished, sepsis and pancreatic cancer.

·        Amylase:  Amylase is produced by the pancreas and GI tract.  It can be elevated if an animal has pancreatitis, kidney disease or GI disease.

·        Cholesterol (Chol):  Cholesterol can be elevated if blood is drawn shortly following a meal and with certain diseases.  There are hypothyroidism, Diabetes, Cushing’s, and certain diseases in the kidney that result in protein loss in the urine.  The cholesterol can be decreased in severe malnutrition, hepatic disease and diseases of the intestines that result in protein loss.

Complete Blood Count (CBC) – this measures the volume of RBC’s, WBC’s, and platelets.  These are important for circulating oxygen, fighting infections and clotting.

·        Hematocrit/Packed cell volume (HCT/PCV):  Can be elevated with dehydration, decreased with anemia.

·        WBC levels:  Can be elevated or decreased with infection or stress response.

·        Platelets:  Can be elevated with dehydration or certain diseases.  Decreases can be a lab error, or an indicator of clotting problems.

 

What tests do we run prior to surgery?

            Seven years or older or a sick animal:  General Health Profile (GHP)

ALB, ALKP, ALT, Amylase, Ca, Chol, Crea, BUN, Glu, Phos, TBIL, CBC

            Less than seven:  Pre-Anesthetic Profile

                        ALKP, ALT, BUN, Crea, Glu, TP, CBC