This week we’ll dive right into the larger and more complex area of the labwork that we refer to as “serum chemistry.” If you recall from the first labwork post, we draw a sample of blood from a pet and split it into two tubes. One is for the complete blood count. The other tube allows the blood to clot. We then spin it in the centrifuge so that the liquid portion is separated from the cells. This liquid portion is called serum. As a quick side note, if you spin down unclotted blood from the purple top, the liquid portion is called plasma. Plasma contains clotting proteins. Serum does not. That’s the major difference. We utilize serum for the chem.
When the results are sent back, we get a big long list of numbers. Each particular thing we look at is named, and we’re given that particular patient’s result. The lab also lists a reference range, which is what “normal” values should be. They also give you a visual slider graph for each value. I’ve cut out a small portion of my own cat’s recent bloodwork as an example.
Alkaline phosphatase (ALKP), Alanine aminotransferase (ALT), Aspartate aminotransferase (AST), Gamma-glutamyl transferase (GGT), and bilirubin are all markers for liver health.
We pay the most attention to ALKP and ALT as a way to see if the liver is being damaged in some way. We typically start to worry when the numbers are two to three times the normal range. ALKP and ALT increases tell us that something is hurting the liver, but they don’t really tell us if the liver’s ability to do its job is compromised. Of course, if these are sky high, we start to assume that so much damage has occurred that function is compromised as well.
Bilirubin to tells us more about the liver’s functional ability. Bilirubin is found in red blood cells, bile, and urine. The liver is responsible for recycling and excreting the bilirubin. When this value goes up, it can mean that the liver isn’t able to recycle the bilirubin the way it’s supposed to. That’s a more direct measure of liver -function-.
Because the liver does so many things, there are a LOT of reasons for liver damage. Infection, cancer, toxins, dental disease, hormone disorders, and trauma can all make these values go up.
The kidneys are monitored with two main values: Blood Urea Nitrogen (BUN) and Creatinine. BUN is a waste product of the body’s use of protein. Creatinine is actually something that is formed in our muscles as a waste product. The kidney is responsible for filtering these two waste products out of the blood so they can excreted in urine.
Calcium and Phosphorus are two elements found in bone and other areas of the body. They are ingested with food and utilized in many areas. The kidneys play a part in helping the body maintain a balance of calcium and phosphorus in the blood, bone, and tissues. When the kidney isn’t functioning normally, these values can go up in the bloodstream.
The kidneys are a complex system, with lots of special rules and considerations for deciding if high BUN and Creatinine are due to a problem within or outside of the kidneys. The bottom line is that if the BUN and Creat results are high, I’m going to be looking for dehydration, kidney failure, or urinary blockage.
We measure two protein levels in the serum. One is the Total Protein (TP), which looks at a combined value for many different proteins in the blood. TP is the sum of the albumin and the globulins. Albumin is a specific protein in the blood. We usually get a direct measured value for that protein. We subtract the albumin from the TP and that leaves just the globulins. Globulins are basically antibodies circulating in the bloodstream. If the TP and the Albumin are low, it means that protein is being lost from the body in some fashion. Massive wounds, kidney failure, and gastrointestinal disease are the most common reasons for low albumin. We don’t usually worry too much if albumin is a bit high. Very high globulins can be a concern, however, for things like chronic inflammation or cancer.
Electrolytes are salts, chemically speaking. When these salts dissolve in the blood, the individual elements are freed to circulate on their own. We look at Sodium (Na), Potassium (K), and Chloride (Cl). These electrolytes are important for nerve impulse conduction, water balance, and muscle contraction (including the heart!). Their levels can be altered by dehydration, kidney damage, urinary blockage, hormone/endocrine diseases, and damage to muscle or blood cells. We pay attention to values that are too high or too low.
Glucose is more commonly known as blood sugar. Diabetes and blood infections are some of the main reasons we see glucose levels change. Head trauma, insulin overdoses, and tiny puppies/kittens that aren’t eating are some other reasons glucose can be outside the normal range.
Thankfully, pets don’t have to worry about coronary artery disease the way people do. We don’t generally distinguish between ‘good’ and ‘bad’ cholesterol in pets. Sometimes, we do have to measure the serum triglycerides, but only in a small specific set of cases/diseases. That being said, if cholesterol is high, we may suspect a problem with a pet’s GI tract or thyroid gland.
Amylase and Lipase
These two values were once used as the main ways to check the pancreas for damage. They’re unreliable as indicators for pancreatic disease, though, and we have a far better test now for pancreatic damage/inflammation. Amylase may go up if the kidneys are failing but it’s far less important than the other kidney values.
A Note on Cancer Testing
One of the most common questions I get is whether we have a blood test for cancer. While we are able to sometimes detect lymphoma on the CBC, there really aren’t widely-used or well-studied blood tests for various cancers. There is a company that is offering testing to help detect cancer. The test does not specify which TYPE of cancer is present. Most of the veterinary oncologists aren’t a big fan of this test because it doesn’t tell you which type, nor where to find it in the patient. It could lead to radiographs, other bloodwork, ultrasounds, organ biopsy… and if all of that comes back normal, then what? There just hasn’t been enough work done on the effectiveness of the test for me to fully promote it. The idea has promise and merit for the future. For the time being, regular examination every 6-12 months is the best tool we have to detect changes.
As always, thanks for reading!