What's In The Blood? Blood Testing And Interpretation

by Dr. Greg Magnusson, DVM

Every day, all day, cells within your body are being constantly replaced. You lose a layer of skin, and a new layer grows up underneath it. You cut your hair, and more hair grows. The same sort of thing happens INSIDE your body all the time, with your internal organs – cells are born, grow, die and are replaced.

Blood carries red and white blood cells, water, and a bunch of chemicals. 

These chemicals include the insides of some of those ruptured cells that are being repaired or replaced, waste products that need to be eliminated, nutrients from the food you eat that need to be processed, toxins that need to be decontaminated, oxygen, carbon dioxide, etc.

The blood carries good stuff, and bad stuff both.

Sampling the blood allows us to detect levels of some of these blood chemicals. Each chemical level is represented by a number. Once upon a time, scientists took hundreds of normal cats and dogs, drew their blood, and measured various chemical levels in these NORMAL patients to decide a NORMAL RANGE.

Let’s say they took 1,000 dogs, and measured their Blood Urea Nitrogen (BUN) levels. If 95% of those 1,000 NORMAL dogs had BUN levels between 7 – 27 mg/dL, we would say that the NORMAL RANGE for BUN is expected in dogs to be somewhere between 7 – 27 mg/dL, with a “95% confidence interval”.

That still means, by the way, that 5% of TOTALLY NORMAL DOGS have BUN levels lower or higher than range – having a result “out of normal range” doesn’t necessarily mean “abnormal”.

A routine blood panel is an overview profile of several of these chemical levels all at the same time. 

A profile might include chemical levels related to the liver, kidneys, bone mineral balance, pancreas, blood cell profile and blood protein content, blood sugar, and cholesterol among other things.

Sometimes, having an elevated level means an organ is being damaged. 

For instance, if your dog has a high Alanine Aminotransferase (ALT), that might suggest some cells of the liver are rupturing more than normal, either from disease, or injury, or infection, or who knows what.

Other times, elevated levels mean the clearing mechanisms aren’t working.

BUN is supposed to be peed out by the kidneys, for instance, so having a high BUN might suggest the kidneys aren’t working well.

Because a blood profile is simply a series of numbers set beside normal ranges, evaluating a blood profile is more of an ART than a SCIENCE. 

An individual abnormal level is often not as important as the overall picture of the profile, as it relates to the clinical signs, symptoms, history, etc. This is why it’s incredibly important for a licensed veterinarian to evaluate your pet’s blood profile.

It’s also why if you have 10 different veterinarians look at the same profile, you might get 10 different interpretations, or guesses, as to what the real problem might be.

Determining what CAUSES an elevation in a particular blood level in a particular pet is what veterinarians spend four years in veterinary school, hours and hours of continuing education every year, thousands of pages of textbooks and years of clinical experience learning.

Even then, a lot of the time a seasoned veterinarian will only have an IDEA of what MIGHT be causing elevations in blood levels, and we have to go with our gut feeling when choosing treatments. Other times we might suggest further testing, either of the blood or by taking x-rays or doing biopsies or whatever, to try to find the primary cause of illness.

It’s critically important for you to find a veterinarian you TRUST to discuss your pet’s health. 

Since none of us are all-knowing, the JOURNEY to finding a diagnosis, and the steps taken along the way to ensure your pet’s comfort and your knowledge, are often just as important as the diagnosis itself.

Blood tests:

Here is a listing of basic blood profile analytes, and some of the conditions that MIGHT cause their elevation in a sick patient. THIS IS NOT INTENDED AS A COMPREHENSIVE RESOURCE and I STRONGLY encourage you to seek veterinary advice if you have a concern about your pet’s health.

ALT - Alanine transferase (al-aneen transfer-ase)	elevated when liver cells are damaged or destroyed.
Phosphorus	elevated during kidney failure, hyperthyroidism in cats, and in normal growing animals. Also may rise with hemolysis. decreased with certain forms of cancer. Elevated OR decreased during rare diseases of the parathyroid gland, which controls blood calcium levels.
t-Bili – Total Bilirubin (billy-ruben)	elevated during liver disease or with extensive red blood cell damage (“hemolysis”: hemo=blood, lysis=rupture).
ALP - Alkaline phosphatase (alk-a-line phos-fat-ase)	elevated during liver disease, certain bone diseases, during blockage of the bile duct (which carries fat-digesting enzymes from the gallbladder to the intestines), or after we give steroids to a pet. Also increased in normal growing pets.
BUN - Blood Urea Nitrogen	elevated during dehydration, kidney disease, or disorders of the urinary tract (including blocked cats).  rarely, can be decreased during starvation or chronic liver disease.
Ca - Calcium	elevated with certain cancers (including lymphosarcoma, bone cancer, peri-anal-gland tumors). Also elevated during kidney failure and disorders of the adrenal glands (Addison’s).  decreased during pancreatitis, antifreeze poisoning, and kidney failure. In the blood, calcium is carried by a blood protein called Albumin. Therefore, if albumin is elevated or decreased, blood calcium levels will elevate or decrease along with it. Falsely, can be increased “just because” and should be rechecked, or can be decreased if you test for calcium using blood from a purple-top (EDTA-containing) tube since EDTA binds calcium.
CREA - Creatinine (cree-a-tih-neen)	elevated during kidney disease or dehydration.
AMY - Amylase (am-i-laze)	elevated when cells of the pancreas are damaged, or during kidney disease (since the kidney is supposed to be filtering amylase out of the blood, if the kidney isn’t working, amylase levels will elevate).
TP - Plasma (“total”) Protein	elevated during dehydration, severe infections or certain cancers.  decreased with a severe liver disease, starvation or severe kidney disease.
ALB - Albumin (al-byoo-min)	a protein found in large quantities in the blood, albumin elevates during dehydration.  more importantly, decreases during starvation, severe intestinal disease, severe liver disease, severe kidney disease or severe intestinal parasitism.
GLOB - Globulin (glob-you-lynn)	globulins are antibodies, small proteins found in the blood that help the body respond to infection, or participate in inflammation.  elevated during infections, chronic inflammation of any tissue, or certain blood cell cancers.
GLC or GLU - Glucose	elevated during stress, after a meal, or with diabetes mellitus.  importantly, decreased with cancer of the pancreas, during starvation (especially in neonates) or shock, or with disorders of the adrenal glands. Falsely, decreased if blood is allowed to sit in a red top tube since red blood cells consume blood sugar.
CHOL - Cholesterol	elevated after a meal, or during blockage of the bile duct (which carries fat-digesting enzymes from the gallbladder to the intestines), hypothyroidism, disorders of the adrenal glands, and kidney disease.  decreased during severe liver disease, diabetes mellitus, and starvation.