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But What Does It Mean?
Most days my electronic
mail box brings at least one such plaintive cry from someone who
has got hold of their dog’s blood results and is now struggling
to understand what on earth they might indicate, with their
crazy acronyms and values that are too high or too low,
sometimes seemingly way out of the normal. This can be one of
those cases where a little knowledge is a very dangerous thing.
It can be highly significant if certain values are even slightly
outside the norm, whereas others have to be many times removed
for it to be of any concern whatever. Even normal values taken
in conjunction with other normal values can be significant as
they trend in one direction or another. Your veterinarian may
want to follow these values over time and repeat certain parts
of the blood work or even the whole thing. Blood results should
never be interpreted without regard to the physical and mental
appearance of the dog. It is always a good idea to get annual
blood work done on your healthy Beardie. Some dogs may have one
or more values that are outside of the laboratory normal, but
this can be quite normal for that dog. It will save a lot of
time if you aren’t scurrying off after red herrings when he gets
sick.
The normal values for
each lab test may vary from laboratory to laboratory. They are
established by measuring the parameters from a number of
apparently normal healthy dogs. They do not usually take into
consideration breed, sex, neuter status or size. They will
consider species, so a dog’s blood should never be sent to a
human lab. An individual substance may be measured using
different tests in some cases in different laboratories.
If your dog is taking any
drugs this should be noted on the submission as certain drugs
will affect laboratory results. If you are giving your dog any
drugs let your veterinarian know, especially if s/he didn’t
prescribe them. It is generally best, unless otherwise
requested, to fast your dog prior to drawing blood. Fat in the
blood – lipemia – can affect a number of levels. Some levels
will also be affected by hemolysis. This is the result of red
blood cells being broken and their contents being lost into the
serum. To avoid hemolysis your veterinarian will usually remove
the stopper from the vacutainer as well as the needle from the
syringe, and not expel the contents of the syringe too fast.
An informed client is a
boon to the veterinarian. Obviously, nothing I write should be
used to diagnose your Beardie’s condition. It may help you ask
the right questions or understand your veterinarian’s concerns,
but nothing more.
Normally when we discuss
blood work we mean two specific groups of tests. The Complete
Blood Count (CBC) requires whole blood. It is just as it says a
numerical count of the various cell types found in the blood.
The biochemistry profile is performed on serum – the supernatant
part of the blood that rises to the surface after the cells have
sunk to the bottom when the blood is spun in a centrifuge. If
the serum is pink it indicates hemolysis, if it is milky or
cloudy it indicates lipemia. Hemolysis
can alter the results for amylase, lipase, ALT, AST, calcium and
phosphorus, while lipemia can affect glucose, sodium, potassium
and protein.
Your veterinarian may order other more specific blood work, but
these are the basic tests I will be covering in this article.
Complete Blood
Count
The CBC measures the
number of cells of different types circulating in the blood.
There are three basic types, red cells, white cells and
platelets. Red cells are made in the bone marrow (the
soft center of the bones). Their function is to carry oxygen
from the lungs to the cells throughout the body. They are
removed from the blood by the spleen and liver. If a Beardie
has too few red cells it is anemic, too many and it has a
condition called polycythemia. Anemia can occur if red cells
are lost to either internal or external bleeding; or if they are
destroyed earlier than normal (hemolysis). It may also be the
result of insufficient production by the bone marrow.
Polycythemia is less common, and usually is the result of
dehydration. Animals living at higher elevations make more red
cells to compensate for the lower amounts of oxygen in the air.
As well as the absolute number of red cells, the CBC will
include the hematocrit (Hct) or packed cell volume (PCV) – the
percentage of red cells in the blood sample. Blood is spun in
very thin tubes, and the red cells settle to the bottom. Above
them is the small “buffy” coat layer of white cells and above
that the plasma which should be clear and colorless. Clear
yellow plasma indicates liver disease – jaundice, white opaque
plasma indicates lipemia, and pink to red clear plasma the
presence of hemoglobin from lysed red cells. Hemoglobin
concentration (Hb) is also measured. Hemoglobin is the
substance in the red cell that carries the oxygen. Mean
corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and
mean corpuscular hemoglobin concentration (MCHC) are all used to
help classify anemia, albeit the most useful measure of anemia
is the reticulocyte count. Reticulocytes are immature red cells
that still contain a nucleus. In anemia they may be released
prematurely to help meet the animal’s need for oxygen. You need
the absolute reticulocyte count not the proportion. As the
numbers of adult red cells drop the proportion of reticulocytes
will rise, and so be less informative.
There are several
different kinds of white blood cells or leukocytes. The CBC
will usually report the percentage as well as the absolute
number. The latter is always the more important number. White
cells are also made in the bone marrow. The most numerous white
cell group are the neutrophils. They are phagocytes –
cells that can engulf and digest foreign substances, and their
primary function is to destroy microbes. They secrete various
substances to help with this, and can also pass through cell
walls, attracted to the foreign invaders. Increased numbers of
neutrophils indicate inflammation, infection by bacteria,
distemper virus, fungi, some parasites, as well as immune
mediated disease, necrosis, endotoxins, foreign bodies,
hemorrhage, hemolysis and Rocky Mountain Spotted Fever.
Prednisone and other corticosteroid drugs can increase
neutrophil numbers, by reducing their stickiness and random
migration from blood to tissues. In general, the response is
greatest if the infection is localized (pyometra for example)
rather than generalized. Numbers are low if destruction exceeds
production. This can result from massive utilization but most
often is due to decreased production or decreased survival.
Chemotherapy, leukemia, ehrlichiosis, parvovirus, immune
mediated diseases, endotoxins or an overwhelming sepsis could
cause this. Lymphocytes are found in lymph nodes,
spleen, thymus, tonsils, lymphoid tissue in the gastrointestinal
tract and respiratory system and bone marrow as well as the
blood. While they cannot be differentiated morphologically they
are of two types T lymphocytes that mature in the thymus and are
involved in cell-mediated immunity and B-lymphocytes that
function as antibodies in the blood. They are the most long
lived white cells and are unique in that they recirculate back
into the blood from the tissues. Recirculation is the process
most likely to influence the number of lymphocytes found in the
blood. Blood count correlates poorly with enlargement of the
lymph nodes. Increased numbers are occasionally seen during
chronic infections. Lymphopenia (low numbers) are relatively
common in sick animals, however. Stress mediated by
corticosteroids (natural or drugs) causes lymphocytes to move
from the blood into lymphoid tissue. This effect is maximal 4
to 8 hours after the appearance of the corticosteroids. Acute
infection, immunosuppression, acquired deficiency as well as
loss or damage to lymph tissue can all reduce lymphocyte
numbers. In puppies, lymphocytes may be elevated due to
infection.
Monocytes
usually parallel neutrophils and increase in infection as well
as in response to corticosteroids. Monocytes transform into
macrophages after a time in circulation, these are large
efficient macrophages with lots more granules and proteolytic
enzymes then monocytes. Macrophages clean out any foreign
particles or dead cells, but are less responsive to infection
than neutrophils. They also present foreign substances to
lymphocytes in a form more likely to elicit an immune response.
Reduced numbers of monocytes are not clinically significant.
Eosinophils are attracted to substances released by mast
cells, and inhibit their further release limiting or delaying
allergic or anaphylactic reactions. Increased level is usually
associated with parasitic infection or hypersensitivity.
Reduced numbers can be the result of an acute infection or the
presence of corticosteroids. Basophils are usually quite
rare. Seeing them is therefore quite significant. They tend
to parallel eosinophils, and tend to increase in dirofilariasis
the early stage of heartworm. If eosinophil levels are normal
but basophil levels are high, serious chronic disease should be
investigated.
Platelets,
also known as thrombocytes, stick to exposed collagen within
seconds after injury and help to form clots to prevent internal
and external bleeding. Reduced numbers indicate either bone
marrow damage or increased rate of destruction. The two major
causes of destruction are immune-mediated thrombocytopenia
(ITP), which may be secondary to tick borne and other
infections, or disseminated intravascular coagulation (DIC), a
complex and usually terminal condition in which blood clots
throughout the body as the result of a number of serious
conditions. Platelet numbers have to drop dramatically before
you see spontaneous bruising – including pinpoint petechiation –
and bleeding.
A blood smear will be
examined microscopically not only as confirmation of the machine
generated cell numbers, but also to look for parasites, as well
as abnormal cell shapes and arrangements. Platelets may clump
in samples giving false low readings and the blood smear will
determine whether adequate numbers are indeed present.
The Biochemistry
Profile
The levels of a variety
of enzymes, electrolytes and other substances are measured in
the blood serum. Serum is the clear (hopefully) fluid left
after the blood cells have been allowed to clot. Together with
urinalysis it provides an overview of the health and function of
many of the body organs. The tests included in the profile can
vary. Idexx, the laboratory I use, offers a wellness check of
11 substances, but also offers tests or 21, 25 and 27 substances
as well as a multitude of add-on tests. Common tests are
presented here.
Albumin
is a small protein produced by the liver. Albumin helps to hold
water in the blood vessels; if albumin levels drop, fluid leaks
out of the blood as it is pumped through the body and
accumulates in body cavities (e.g. ascites) or in tissues as
edema. Albumin is decreased due to intestinal malabsorption or
malnutrition; exocrine pancreatic insufficiency (EPI) which
results in fewer enzymes to digest protein; or chronic liver
disease. Reduced levels also occur if protein is lost through
kidney disease or hemorrhage. Burns and certain other skin
diseases can cause loss of protein through the skin. Increased
albumin is the spurious result of dehydration.
Total protein
includes albumin, fibrinogen and globulins. Fibrinogen is
involved in the formation of blood clots and levels increase in
inflammation or neoplastic disease. It may also be increased
mildly if the animal is dehydrated. It can be, but is not
normally, measured separately as part of the profile.
Globulins are larger proteins commonly referred to as
antibodies. Often globulin is listed as total protein minus
albumin, more accurate assays separate not only albumin from
globulin but alpha, beta and gamma globulins from each other.
Alpha globulins are acute reacting antibodies responding to
tissue injury and inflammation, beta globulins are associated
with acute liver disease, and gamma globulins are associated
with chronic inflammatory diseases, immune mediated diseases and
some lymph based cancers. Some reports will include the ratio
of albumin to globulin.
Alkaline phosphatase
(ALP) is a
group of enzymes that originates from every tissue in the body.
High activities occur in liver, bone, intestine, kidney,
placenta and white blood cells. Although not normally done, the
enzymes from the various organs can be isolated and measured.
In healthy animals most ALP is of liver origin. Increased ALP
can indicate liver disease (due to interruption of bile flow),
bone disease (osteosarcoma, bone healing or hyperparathyroidism)
or increased blood cortisol either because corticosteroids have
been given or due to Cushing's disease (hyperadrenocorticism).
Other drugs especially phenobarbital can also increase ALP. In
acute liver disease, ALP may remain normal while other liver
enzymes rise, but ALP levels may continue to rise during
recovery. In geriatric dogs certain malignant cancers (mammary,
squamous cell carcinoma and hemangiosarcoma) may produce a very
high ALP.
Alanine
aminotransferase (ALT)
{aka as glutamic pyruvic transaminase (SGPT)} is an enzyme
considered liver specific in the dog. Liver damage – sublethal
damage or necrosis - causes ALT to increase in the bloodstream.
The level of increase reflects the number of cells that have
been damaged. In acute disease a reduction in ALT is favorable,
but in chronic cases may just reflect that most of the liver is
already compromised. Elevation in ALT does not provide
information as to whether the liver disease is reversible or
not.
Aspartate
aminotransferase (AST)
{aka glutamic oxaloacetic transaminase (SGOT)} occurs in most
cells but is considered diagnostic of liver and muscle disease.
It is less specific and less sensitive to liver damage than
ALT.
Other enzymes used to
detect liver injury include gamma glutamyl transferase (GGT) and
sorbitol dehydrogenase (SDH).
Bilirubin
is produced by the liver, spleen and bone marrow as they recycle
old red blood cells. Most bilirubin is conjugated in the plasma
with proteins although some will be free. In the case of
hemolytic anemia or internal hemorrhage most of the increase
will be free bilirubin. Blockage of bile flow – either in the
liver of gallbladder leads to an increase in conjugated
bilirubin. Acute and chronic liver disease usually produces a
combined response with increases in both types. Large amounts
of bilirubin in the bloodstream will give a yellow color to the
mucus membranes, inside the ears and eye whites. This is called
icterus or jaundice. Bilirubin is further broken down and
eliminated in both the urine and stool. In dogs increases in
bilirubin in urine precedes that in the serum.
Bile acids
Cholic acid and chenodeoxycholic acid are produced by the liver,
combined with amino acids glycine and taurine and secreted into
the bile to assist in fat digestion and absorption as well as
absorption of the fat soluble vitamins. They are stored in the
gall bladder. A bile acid test is used to evaluate the function
of the liver and its blood flow to the liver, and to diagnose
dogs with portosystemic, shunt, where blood from the intestines
by-passes the liver and goes straight to the general
circulation. The bile acid test measures a fasting blood sample
and a blood sample two hours after eating. In normal dogs, bile
acids released to digest a meal are recovered into the portal
blood and returned to the liver. If the dog has a portosystemic
shunt the bile acids enter the general circulation and will be
dramatically elevated.
Blood Urea Nitrogen
(BUN) Only
small amounts of urea are ingested, most is made from ammonia –
either from the break down of protein or absorbed from the large
intestine – in the liver. Urea is excreted by the kidneys.
Increased protein breakdown due to increased protein in the
diet, hemorrhage, necrosis, starvation, prolonged exercise,
infection, fever or corticosteroids causes a mild increase in
BUN. Decreased perfusion of the kidneys caused by dehydration,
shock or cardiovascular disease can also increase BUN. In dogs
with kidney disease approximately 75% of the kidneys are
nonfunctional before BUN will increase. BUN doubles
approximately each time the remaining number of nephrons is
halved.
Creatinine
A small amount of creatinine may be ingested from diets rich in
muscle meats. Most, however, comes from the conversion of
energy stores of phosphocreatine in the muscles to creatinine -
a waste product that is eliminated from the body by the
kidneys. The creatinine pool is influenced by muscle mass,
which in turn can be affected by muscle disease, wasting and
training. Unlike BUN, creatinine is less influenced by diet or
urine flow, and elevation of creatinine is the result of kidney
disease or dehydration.
Amylase
is an enzyme produced by the pancreas, small intestine and
liver. Amylase helps the body break down sugars. In healthy
animals serum amylase is non-pancreatic in origin. In
pancreatitis (inflammation of the pancreas) or pancreatic cancer
amylase can leak into the lymph system and from there to the
blood. The higher the level (3 to 4 times normal) the more
likely the source is the pancreas. Kidney disease and
intestinal obstruction can also increase amylase;
corticosteroids can increase it or decrease it. Occasionally,
animals with pancreatitis can have normal serum levels of
amylase. Because pancreatic disease isn’t the only cause of
increased amylase, levels are assessed in conjunction with those
of lipase.
Lipase
is another pancreatic enzyme which is responsible for the
breakdown of fats. It takes longer to get a lipase measurement
than that of amylase. A two-fold or greater increase in lipase
indicates acute pancreatic disease, and it is almost never
normal if the dog has pancreatitis. However, increase can
occur in kidney or liver disease or with corticosteroids.
Creatine phosphokinase
(CK, CPK) CK
is an enzyme that helps store and release energy from muscle.
In healthy dogs levels vary considerably with age, at one day
old puppies have 5 times the activity of adults. Adult levels
are reached at 7 months of age. Old dogs may have lower levels.
Levels may be artificially increased by hemolysis, excess
bilirubin or muscle derived from difficult or repeated
venipuncture. Elevation may indicate infection; myositis;
trauma; degenerative, metabolic, ischemic or nutritional
myopathy and involve heart muscle as well as skeletal muscle.
The increase does not correlate to the extent of the damage.
Even minor insignificant damage can cause elevation in CK. Two
other enzymes -lactate dehydrogenase (LDH) and aspartate
amintransferase (AST, GOT) - may also be measured to determine
muscle function. Results tend to mirror CK, but they are less
sensitive.
Glucose
is blood sugar. Its level is regulated by the pancreatic
hormones insulin and glucagon. Insulin increases the uptake of
glucose by liver, skeletal muscle and fat primarily, as well as
uptake of some other simple sugars, amino acids, fatty acids,
potassium and magnesium. Glucagon is released in response to
low blood sugar and causes the liver to convert stored glycogen
into glucose. Corticosteroids antagonize insulin’s effects.
Glucose is increased in dogs and cats with diabetes mellitus –
lack of insulin. It may be mildly increased in dogs with
Cushing's disease. (Glucose can temporarily increase in the
blood if the dog is stressed by having blood drawn or the
general examination. If glucose is also elevated in the urine,
the blood glucose elevation is not transient.) Low blood sugar
occurs less commonly and can be indicative of pancreatic cancer
or overwhelming infection (sepsis) or administration of
excessive insulin. It may also indicate improper handling of
the sample. An animal with low blood sugar will be depressed,
seizuring or even in a coma.
Cholesterol
There are four major fats in plasma; the two most often measured
are cholesterol and triglycerides. They travel bound to
peptides in complexes called lipoproteins. Cholesterol levels
are usually inversely related to thyroid hormone activity, and
it is one of the best indicators of thyroid disease. Liver
disease, acute pancreatitis, diabetes mellitus, and kidney
disease (nephritic syndrome) and corticosteroid drugs, but not
Cushing’s disease, can also elevate cholesterol. High
cholesterol does not predispose dogs to cardiovascular disease.
Triglycerides
must be measured in fasting samples. Elevation indicates
endocrine (pancreatic, thyroid), liver, kidney or exocrine
pancreatic disease.
The electrolytes usually
measured include sodium (Na+), potassium (K+),
chloride (Cl-) and TCO2
- which is primarily a measure of bicarbonate HCO3-).
The sum of positive ions minus the sum of negatively charged
ions is called the anion gap, and is used to determine acid base
abnormalities. It increases in such diseases as lactic
acidosis, diabetes mellitus, ketosis, renal insufficiency and
some toxicities like ethylene glycol (antifreeze) poisoning. A
decrease is rare.
Sodium
is essential for proper kidney function and water retention.
The correct balance between sodium and potassium ions inside and
outside nerve and muscle cells is essential for their proper
function. Low blood sodium is most commonly seen with Addison's
disease (hypoadrenocorticism), but can also be seen in diabetes
mellitus or an animal that has been vomiting.
Potassium
is increased in the dogs with Addison’s disease, as well as with
acute kidney failure, and in animals with a ruptured or
obstructed bladder. Low potassium is associated with anorexia,
vomiting, diarrhea, diabetes or the use of diuretics. Many
profiles calculate sodium potassium ratios. If this number is
greater than 27 it indicates Addison’s disease.
Chloride
changes tend to parallel those of sodium, but loss of stomach
hydrochloric acid can result in low chloride and normal sodium.
TCO2
Loss of bicarbonate can occur through diarrhea. Loss can also
be relative to a build up of lactic acid, ketones, or uremic
acids in kidney failure. Some organic poisons may also lower
blood acidity. In cases of loss of stomach acid, the kidneys
may excrete more bicarbonate to compensate.
Calcium
The levels of calcium potassium and magnesium are regulated by
parathyroid hormone, calcitonin from the thyroid and Vitamin D.
Serum calcium is a reflection of relative bone formation and
reaborption. It is rarely affected by dietary intake. High
blood calcium is most commonly associated with cancer. Less
common causes of elevated calcium are chronic kidney failure,
primary hyperparathyroidism, poisoning with certain types of
rodent bait and bone disease. Low blood calcium may occur in
bitches shortly before giving birth or during the early nursing
period. This is called eclampsia. It causes tetany, the muscles
become rigid. Hypofunction of the parathyroid will also result
in low blood calcium. Dogs poisoned with antifreeze may have
very low blood calcium.
Phosphorus
Levels will be higher in young animals than in adults. Serum
phosphorus is largely regulated by the kidneys, although
parathyroid hormone can increase resorption. Dietary intake can
directly affect serum levels. Phosphorus is increases in
chronic kidney disease, as with BUN and creatinine, phosphorus
increases in these patients when about 75 percent of both
kidneys is damaged.
Blood serum as well as urine components can vary markedly
throughout the day. Taking blood from a fasted dog will
minimize those variations, but fail to show nutrient sensitive
diseases. Blood glucose will be low, as will insulin, while
glucagon secretion will be elevated. In anorexic patients, or
those fasted more than 24 hours, fat will start to break down
excessively to provide energy and increase levels of ketones
which might make the blood more acid. In a dog that has been
eating, elevated ketones would suggest it had diabetes or liver
disease, however. BUN and phosphorus decrease in anorexic
patients, so that renal failure might be missed. Fortunately
creatinine levels will not be affected. Fasting for 24 hours
increases the resorption of sodium and excretion of potassium by
the kidney. More calcium, magnesium, uric acid and ammonia will
also be excreted. In general, fasting 6 to 12 hours before a
blood draw is optimal. If lipemia persists after fasting for 24
hours it indicates problems with fat metabolism. If the purpose
of the blood test is to evaluate the effect of dietary
modification on a disease process, blood should be drawn 2 to 6
hours after food consumption. If you are reevaluating the
thyroid levels of a dog already receiving supplementation, blood
should be drawn 4 to 6 hours after the morning pill. At this
point thyroid levels will be maximal, and should be in the upper
50% of lab normal to 150% of the upper limit.
I
have not described urinalysis here. However, to fully evaluate
the health of a dog I would recommend performing one as part of
the wellness check-up. Urine can 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.
I hope that this
presentation will assist you in understanding the results of
your dog’s blood test. It is by no means meant to replace the
services of your veterinarian in treating your dog.
Linda Aronson, DVM.
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A grateful thank you to
Linda Aronson, DVM for the use of her articles
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