Blood work: What it means and why your pet needs it (Part 2: Blood Chemistry)

Turns out this topic is gathering some steam here on Dolittler––as it is in veterinary minds across the spectrum of companion animal medicine. That’s why this topic requires a two-post treatment to properly address. 

Though blood work is an increasingly common component of every pet’s medical care, not every veterinarian will draw your pet’s blood automatically. That’s why you need to understand why we do so and what we hope to learn by gathering this kind of [sometimes expensive] evidence.

For your better understanding, here are the typical reasons we’ll go so far as to poke your pet and recover their “red gold”:

• Because he’s sick and we’re unsure why or need more information about how his body is responding to a certain disease or process. 
• Because her disease is worsening or improving in ways we need to measure so that we can adjust our treatments (medications, etc.).
• Because we’re considering a treatment regimen for your pet that requires long-term medications that can do damage to pets with certain risk factors (such as pain relievers for osteoarthritis in pets with pre-existing liver or kidney disease). 
• Because your pet needs an anesthetic procedure and we want her to be as safe as possible throughout this process. Some diseases or disorders require that we change our protocols or defer anesthesia should they be present.
• Because we like to keep an annual record of your pet’s basic bodily functions and blood work is one way to objectively measure these. Keeping track of how these change is often crucial to how we optimize your pet’s care. 

That said, let me first reiterate: The most common kinds of blood work are aimed at comprehensively testing the body’s functions and searching for signs of disease and disorder. They include the CBC (see yesterday’s post) and blood chemistry (AKA, “chemistry” or “chem”). 

If the CBC (complete blood count) tests the blood cells themselves, the blood chemistry is all about testing the fluid the blood cells utilize to course through a pet’s body. This fluid’s components reflect the chemical elements utilized, filtered or produced by certain organs, thereby offering up information on their basic health and potential “dis-ease.”

Makes sense, right? 

More specifically, here are the “chemicals” we like to measure most commonly and why:

LIVER FUNCTION

These elements indicate, in a general way, how well a pet’s liver is functioning.

• alkaline phosphatase (“alk phos,” SAP or ALP)

Liver injury, drugs, bone injury, skeletal diseases, cancer, pregnancy and normal growth can all elevate this enzyme’s level. Gastrointestinal diseases and endocrine diseases (like Cushing’s) can also raise its levels. Too low? Protein and vitamin deficiency (and severe, end-stage liver disease) can deplete it. 

• alanine transaminase (alanine aminotransferase, ALT)

Toxins, drugs, liver damage and kidney infections can all raise it. Decreased bile flow can drop it (as when a liver is “congested”). Mild elevations don’t stress us (in the absence of symptoms), but follow-up blood work is always necessary in these cases.

• bilirubin total (T Bili)

Toxicity (poisoning), some forms of anemia and liver disease can all raise this measure of bile pigment (produced by the liver). Certain kinds of malnutrition, too-fatty diets and an end-stage, diseased liver may be accompanied by its low levels. 

• albumin

This protein is produced by the liver. As such, its depletion tells us something might be up with this organ. But malnutrition can do it, too. Fever, infection, burns, swelling and low calcium levels are also likely to drop albumin levels. While rarely elevated, severe dehydration may sometimes raise it a bit. 

KIDNEY FUNCTION

When we say we’re testing your pet’s kidney function with blood work, these are the most common tests we look at. 

• blood urea nitrogen (BUN)

Kidney damage is what we think of first when the BUN (usually pronounced “B.U.N.”, not “bun”) is up. But certain drugs, intestinal bleeding, excessive protein intake, dehydration and extreme exercise can raise it. When it’s low,  we tend to think poor nutrition, poor gastrointestinal absorption or even liver damage in some cases. 

• creatinine

Because the kidneys are supposed to filter out this chemical, its elevation always points us in the direction of kidney damage or dehydration. Muscle breakdown (as with extreme exercise) can also flood the body with creatinine while certain drugs can impair the kidney’s filtration of it. Confusingly, low levels may indicate kidney damage, protein starvation, liver disease, or pregnancy. 

• creatine kinase (CK, CPK)

This enzyme usually indicates either kidney trouble, dehydration or muscle breakdown, as with extreme stress, injury or exercise.

ELECTROLYTES

These individual elements are measured to determine the interaction of a myriad of complex processes. They may go along with certain illnesses or disorders and knowing their true value helps us guide our treatment options, especially when it comes to fluid therapy.  

• sodium

Sodium (Na) is lost with vomiting and diarrhea. It can help indicate a pet's hydration status. Pets with Addison's disease and kidney disease may also have low levels. 

• potassium

Low levels of potassium (K) are seen with acute vomiting and diarrhea. Kidney failure and other kidney troubles, Addison's disease, dehydration and urinary obstruction will raise it. Extremely high levels, as we often see in "blocked" cats can lead to deadly cardiac arrhythmias. 

• chloride

Chloride (abbreviated Cl) is often low in acute vomiting. Addison's disease patients will also show lower levels. Elevations are commonly associated with dehydration. 

PANCREATIC FUNCTION

The pancreas is a sensitive gastrointestinal and endocrine (hormone-producing) organ that’s easily insulted. Pets with high levels of the following two enzymes may be experiencing acute (sudden-onset) or chronic (long-standing) pancreatitis. High amylase levels can also be associated with kidney diseases. 

• amylase 
• lipase

OTHER BASICS

• glucose

Got diabetes? Stressed? Depleted your blood sugar with seizures? Has your tiny-breed puppy suddenly collapsed? Has she perhaps eaten some poisons (like Xylitol)? Glucose is the go-to test for so many troubles it’s impossible to list them all here. In any case, this “blood sugar” molecule, whether too high or too low, is a common indicator of mild and serious problems, alike. 

• total protein

Vomiting, diarrhea, liver disease, poor nutritional gastrointestinal malabsorption, dehydration will all raise it. Lupus, liver disease, chronic infections and leukemia will all drop it. 

• calcium

Calcium (Ca) levels can indicate a variety of disease processes. Some tumors, certain hormonal diseases (hyperparathyroidism) and kidney disease can all affect this value. 

***

That’s my summary. But don’t be fooled: the complex interaction of components in the blood, coupled with other processes as they invariably are, may make interpreting these findings not-so straightforward (and that's an understatement). When one goes up, another may come down––and vice-versa. 

That’s why an understanding of these test results is a necessarily “holistic” process in which we take our individual patients’ findings (on physical, CBC, other lab tests, X-rays and/or more sophisticated imaging) and put them all together. Even then, it’s nowhere like it is on Star Trek.

Sigh...if I only had a Tricorder...

WRITTEN BY

Patty Khuly, DVM

Veterinarian