What Do Those Lab Tests Mean?
This information is not meant to be a substitute for veterinary care.
Always follow the instructions provided by your veterinarian.
The results of laboratory tests on a patient are compared to reference ranges
established by measuring the laboratory parameters in a group of normal animals.
The reference ranges for each laboratory test differ between laboratories and
across species. Be careful interpreting laboratory tests. An occasional animal
will have a value for a laboratory test that falls outside the reference range,
but the value may still be normal for that animal.
Your veterinarian will interpret laboratory tests in light
of the entire evaluation of your pet. Sometimes laboratory tests need to be
repeated to evaluate trends, which may provide more information than measurement
of a single test.
The results of laboratory tests may be influenced by drugs
your pet is receiving and some are influenced by a recent meal. Always provide
your veterinarian with information about any drug your pet is receiving. Inquire
when you make an appointment for veterinary care, whether you should fast your
pet before the visit in case laboratory samples are collected.
Complete blood count (CBC)
The complete blood count measures the number of cells of
different types circulating in the bloodstream. There are three
major types of blood cells in circulation; red blood cells
(RBC), white blood cells (WBC), and platelets. Red blood cells
are produced in the bone marrow, which is the soft center of
bones. RBCs pick up oxygen brought into the body by the lungs,
and bring that oxygen to cells throughout the body. Red blood
cells live in the blood stream for about 100 days although the
actual time varies with the type of animal. Old red blood cells
are removed from the blood stream by the spleen and liver. Red
blood cell numbers can be decreased (anemia) if they are not
produced in adequate numbers by the bone marrow, if their life
span is shortened (a condition called hemolysis), or if they are
lost due to bleeding. Increased red blood cell numbers is called
polycythemia and is usually due to concentration of the blood
due to dehydration.
The complete blood count also includes a measure of hemoglobin,
which is the actual substance in the red blood cell that carries
oxygen.
There are several types of white blood cells in blood, including
neutrophils (PMNs), lymphocytes, monocytes, eosinophils and
basophils. Lymphocytes are produced in lymph nodes throughout
the body. The other white blood cell types are produced in the
bone marrow along with the red blood cells and platelets. The
majority of white blood cells in circulation are neutrophils,
which help the animal fight infections. Neutrophils can be
decreased in pets with bone marrow disease, in some viral
diseases, and in some pets receiving cancer chemotherapy drugs.
Neutrophils are increased in pets with inflammation or infection
of any part of the body and in pets receiving prednisone or
other cortisone-type drugs.
Lymphocytes also help fight infection and produce antibodies
against infectious agents (viruses, bacteria, etc.). Lymphocytes
may be increased in puppies and kittens with an infection, they
can be decreased in pets who are severely stressed, and
lymphocytes might be lost in some types of diarrhea. Certain
drugs, such as prednisone (a cortisone-type drug) will decrease
the number of lymphocytes in the blood stream.
Monocytes may be increased in pets with chronic infections.
Eosinophils and basophils are increased in pets with allergic
diseases, or parasitic infections (worms, fleas, etc.).
Platelets are produced in the bone marrow and are involved in
the process of making a blood clot. Platelets live a few weeks
and are constantly being produced by the bone marrow. Low
platelet counts occur if the bone marrow is damaged and doesn’t
produce them, or if the platelets are destroyed at a faster rate
than normal. The two primary causes of platelet destruction are
immune-mediated destruction (ITP or IMT) and DIC (disseminated
intravascular coagulation). Immune-mediated thrombocytopenia
happens when the animal’s immune system destroys platelets. DIC
is a complex problem in which blood clots form in the body using
the platelets faster than the bone marrow can produce new ones.
Animals with a low platelet count bruise easily and may have
blood in their urine or stool.
Packed cell volume (PCV) (called hematocrit, HCT, in humans) is
another measure of red blood cells. A small amount of blood is
placed in a tiny glass tube and spun in a centrifuge. The blood
cells pack to the bottom of the tube and the fluid floats on
top. The PCV is the percent of blood, that is cells, compared to
the total volume of blood. In normal dogs and cats, 40-50% of
the blood is made up of blood cells and the remainder is fluid.
Blood and urine tests are performed to get an initial overview of the health,
and sometimes the function, of body organs. Some blood tests are very specific
for a single organ, whereas other tests are affected by several organs. Blood
tests are often performed as a biochemistry profile, or chemistry panel, which
is a collection of blood tests to screen several organs at one time. The makeup
of a biochemical profile varies with the laboratory in which it is performed.
Following are some of the more commonly performed chemical tests:
Albumin is a small protein produced by the liver. Albumin acts as a
sponge to hold water in the blood vessels. When blood albumin is decreased,
the pressure created by the heart forcing blood through the blood vessels
causes fluid to leak out of the blood vessels and accumulate in body
cavities such as the abdominal cavity or in tissues as edema. Albumin is
decreased if the liver is damaged and cannot produce an adequate amount of
albumin or if albumin is lost through damaged intestine or in the urine due
to kidney disease. The only cause of increased albumin is dehydration.
Alkaline phosphatase originates from many tissues in the body. When
alkaline phosphatase is increased in the bloodstream of a dog the most
common causes are liver disease, bone disease or increased blood cortisol
either because prednisone or similar drug is being given to the pet or
because the animal has Cushing's disease (hyperadrenocorticism). In cats,
the most common causes of increased alkaline phosphatase are liver and bone
disease.
ALT is an enzyme produced by liver cells. Liver damage causes ALT to
increase in the bloodstream. ALT elevation does not provide information as
to whether the liver disease is reversible or not.
Amylase is an enzyme produced by the pancreas and the intestinal tract.
Amylase helps the body breakdown sugars. Amylase may be increased in the
blood in animals with inflammation (pancreatitis) or cancer of the pancreas.
Sometimes pancreatitis is difficult to diagnose and some dogs and cats with
pancreatitis will have normal amounts of amylase in the blood. Lipase is
another pancreatic enzyme which is responsible for the breakdown of fats and
which may be increased in patients with pancreatic inflammation or cancer.
Bile acids are produced by the liver and are involved in fat breakdown.
A bile acid test is used to evaluate the function of the liver and the blood
flow to the liver. Patients with abnormal blood flow to the liver, a
condition known as portosystemic shunt will have abnormal levels of bile
acids. The bile acid test measures a fasting blood sample and a blood sample
two hours after eating.
Bilirubin is produced by the liver from old red blood cells. Bilirubin
is further broken down and eliminated in both the urine and stool. Bilirubin
is increased in the blood in patients with some types of liver disease,
gallbladder disease or in patients who are destroying the red blood cells at
a faster than normal rate (hemolysis). Large amounts of bilirubin in the
bloodstream will give a yellow color to non-furred parts of the body, which
is called icterus or jaundice. Icterus is most easily recognized in the
tissues around the eye, inside the ears and on the gums.
BUN (blood urea nitrogen) is influenced by the liver, kidneys, and by
dehydration. Blood urea nitrogen is a waste product produced by the liver
from proteins from the diet, and is eliminated from the body by the kidneys.
A low BUN can be seen with liver disease and an increased BUN is seen in
pets with kidney disease. The kidneys must be damaged to the point that 75%
of the kidneys are nonfunctional before BUN will increase. Pets that are
severely dehydrated will have an increased BUN as the kidneys of a
dehydrated patient don’t get a normal amount of blood presented to them, so
the waste products do not get to the kidneys to be eliminated.
Calcium in the bloodstream originates from the bones. The body
has hormones, which cause bone to release calcium into the blood and to remove
calcium from the blood and place it back into bone. Abnormally high calcium in
the blood occurs much more commonly than low calcium. High blood calcium is most
commonly associated with cancer. Less common causes of elevated calcium are
chronic kidney failure, primary hyperparathyroidism which is over-function of
the parathyroid gland, poisoning with certain types of rodent bait and bone
disease.
Low blood calcium may occur in dogs and cats just before
giving birth or while they are nursing their young. This is
called eclampsia and occurs more commonly in small breed dogs.
Eclampsia causes the animal to have rigid muscles which is
called tetany. Another cause of low blood calcium is malfunction
of the parathyroid glands which produce a hormone (PTH) that
controls blood calcium levels. Animals poisoned with antifreeze
may have a very low blood calcium.
Cholesterol is a form of fat. Cholesterol can be increased in
the bloodstream for many reasons in dogs. It is much less common
for cats to have increased cholesterol. Some of the diseases
that cause elevated cholesterol are hypothyroidism, Cushing's
disease, diabetes and kidney diseases that cause protein to be
lost in the urine. High cholesterol does not predispose dogs and
cats to heart and blood vessel disease as it does in people.
Creatinine is a waste product that originates from muscles and
is eliminated from the body by the kidneys. An elevation of
creatinine is due to kidney disease or dehydration. Both
creatinine and BUN increase in the bloodstream at the same time
in patients with kidney disease.
Creatinine kinase (CK) is released into the blood from
damaged muscle. Elevation of creatinine kinase therefore
suggests damage to muscle including heart muscle.
Glucose is blood sugar. Glucose is increased in dogs and cats
with diabetes mellitus. It may be mildly increased in dogs with
Cushing's disease. Glucose can temporarily increase in the blood
if the dog or cat is excited by having a blood sample drawn.
This is especially true of cats. A quick test to determine
whether a glucose elevation is transient or permanent is to look
at the urine. If the glucose is chronically elevated there will
be an increased amount of glucose in the urine as well.
Low blood sugar occurs less commonly and can be a sign of
pancreatic cancer or overwhelming infection (sepsis). Low blood
sugar can cause depression or seizures. Low blood sugar can be
seen if the blood sample is improperly handled. Red blood cells
will use glucose so typically red blood cells are removed from
the blood sample and the clear part of the blood (plasma or
serum), is used for analysis.
Phosphorus in the bloodstream originates from bones and is
controlled by the same hormone, PTH (parathyroid hormone) which
controls blood calcium. Phosphorus is increased in the
bloodstream in patients with chronic kidney disease. Like BUN
and creatinine, phosphorus increases in these patients when
about 75 percent of both kidneys is damaged.
Potassium is increased in the bloodstream in the pet with
acute kidney failure such as kidney failure caused by antifreeze poisoning, in
dogs with Addison's disease and in animals with a ruptured or obstructed
bladder.
Potassium is lost from the body in vomit, diarrhea and
urine. Pets that are not eating may have a low blood
potassium. Low blood potassium can cause the pet to feel
weak. Cats with low potassium may develop painful muscles.
Sodium may be slightly increased in the blood if the patient is
dehydrated although many dehydrated dogs and cats have a normal blood
sodium. Low blood sodium is most commonly seen with Addison's disease
(hypoadrenocorticism).
Total protein includes albumin and larger proteins called globulins.
Included in the globulins are antibodies which are protein molecules. Total
protein can be increased if the dog or cat is dehydrated or if the pet's
immune system is being stimulated to produce large amounts of antibody.
Total protein is decreased in the same situations which reduce albumin or if
the pet has an abnormal immune system and cannot produce antibodies.
Urinalysis: A urine sample can provide information about several organ
systems. The concentration, color, clarity and microscopic examination of
the urine sample can provide diagnostic information.
Urine may be
obtained by catching a sample during normal urination, by passing a catheter
into the bladder or by placing a small needle through the body wall into the
bladder, a procedure called cystocentesis. Depending upon why the urine
sample is being collected, one collection method may be preferred over
another. Inquire at the time you make an appointment for veterinary care if
a urine sample may be collected. Preventing your pet from urinating prior to
the appointment will assure that your pet’s bladder will contain urine for
sampling.
Washington State University assumes no liability for injury to you
or your pet incurred by following these descriptions or procedures.
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