Why does my dog need blood work?
A typical hour in the life of a “Veterinary Assistant” based
on my own experience:
Mrs. Smith brings her 5 year old dog, Bugsy, to the clinic
because she’s been vomiting for the past two days (Bugsy, not Mrs. Smith.) I
show them into an exam room, take a history, and wait for the
veterinarian to come in. I hold Bugsy and tell her what a good girl she is as
the vet examines her. The vet builds a diagnostic plan, which includes blood
work and xrays, and leaves the room to get an estimate together. As the
Veterinary Assistant, it’s my job to show Mrs. Smith the estimate and have her
sign it to indicate that she understands her financial responsibility.
Unfortunately, I really have no freaking clue why the dog needs a “Complete
Blood Count” so all I can do is pretend to know what I’m talking about and hope
that Mrs. Smith doesn’t ask too many questions. Mrs. Smith, whose human
children are in college, is on a tight budget (as we all are) but feels
obligated to consent to everything because she wants to be a “good pet owner.” I
take Bugsy to the treatment area to draw her blood as Mrs. Smith sits in the
exam room wondering if Bugsy really needs all of those tests. END SCENE.
Sound familiar? 99% of everyone who has ever owned a dog or
cat can relate to Mrs. Smith. As a future veterinarian, I have been on every
side of this situation. I’ve been the concerned cat owner, the frustrated vet
assistant, and now the person who is ordering the tests. It sucks for everyone
involved. This situation could have been easily avoided with a little
communication and client education on the doctor’s part.
What I’d like to accomplish with this article is to take the
time and SHOW (not tell) you why your dog (or cat) needs blood work. Veterinary
medicine is unique in that we don’t have the ability to ask our animals what
hurts. If you have a UTI, you can tell the doctor “Yes! My bladder hurts and it
burns when I pee. My back also feels a little achy.” A cat may act a little off
if she is feeling sick but she may not. She may be acting perfectly normal even
though it feels like she is peeing fire. And she doesn’t speak English so there’s
that. For those reasons, we must rely on diagnostic indicators in a way that we
don’t have to in human medicine.
So here goes. Put on your white coat, your stethoscope, and
join me in the exam room.
Lela is a 3 year old, spayed female Cocker Spaniel. For the
past two days, she has been lethargic, restless, and hasn’t wanted to eat. We
examine her and note that she is weak, has a fever of 104.4°F, her
heart is racing, her gums are pale and yellowish, and she is panting. Our next
step is to come up with a list of conditions and problems that could cause one
or more of these symptoms. These are called differential diagnoses. This is our
list of diseases to rule out.
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- heart disease
- anemia
- bacterial infection
- viral infection
- liver disease
- iron deficiency
- kidney disease
- bone marrow problems
- tumor somewhere
- parasites that infect red blood cells, e.g. Babesia
- immune-mediated diseases
- “food poisoning”
- toxicity of some kind, e.g. eating onions
- rodenticide poisoning
- antifreeze poisoning
- any disease that causes red blood cells to break apart
This is actually a short list. I’m not smart enough to list off
every single possible disease but you get the idea. There are SO MANY things
that can cause these generic problems.
We now have two options:
1. Do further diagnostic testing to try to narrow it down.
2. “Spray and Pray”-throw some antibiotics and maybe an NSAID
(think Aleve in humans) at it and hope that it resolves.
I think we can agree that “Spray and Pray” is probably not the
best option here. Let’s generate an estimate for some diagnostic tests and see
what Lela’s mom wants to do. Lela’s mom is recently divorced and finances are
really tight right now. We decide to start with a basic workup, a Complete
Blood Count aka CBC, and go from there. We take Lela to the treatment area and
draw her blood. Our assistant takes Lela back to her mom while we run the test.
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| Blood smeared onto a slide provides valuable information! |
We put a sample of blood into our fancy dancy blood machine and
prepare a slide to look at under the microscope. Just looking at the blood
under the microscope can reveal a ton of information. Are the red blood cells normal in size and color? Are there too many? Too few? Are there too many immune
system cells floating around? Are there any parasites on the cells or swimming
in the blood? Are there immature
red blood cells floating around? This can be an indication that the body is
working at overtime trying to make new cells and is spitting them out even
before they’re ready.
We look at Lela’s blood smear and immediately notice something
abnormal. Lela’s red blood cells are clumping together. This is called
agglutination and usually indicates that there is something “sticky” on the
surface of the cells that should not be there.
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Notice the red circles (red blood cells)
clumping together. The purple things are immune system soldier cells. It is
normal to have a certain number of those patrolling the blood.
|
Compare Lela's smear to a normal blood smear:
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You can see that all of the red blood cells are minding their own
business and not sticking together. There are a few immune cells hanging
out.
|
Ok. What we know so far is that the cells are clumping
together. You may not be able to see it but just trust me when I say that there
are also fewer cells than there should be.
As we finish looking at the microscope, the blood machine
prints out the results of the Complete Blood Count (CBC.) A CBC machine counts
the number of different cells in the blood. It tells us how many red blood
cells, platelets, and immature red blood cells we have. It also tells us if the
cells are paler, darker, smaller, or larger than they should be.
Lela’s results:
I realize that this literally means nothing to you. When I saw
this for the first time I considered dropping out of school to become a sexy plus-size lady mechanic or something. It took a whole semester for me to get it down. Don’t be scared. I’m going to walk us through this. If it overwhelms you, don't even look at it. I really just wanted to give you an idea what blood work results look like. The “L” and the “H” beside each value means that it is either Lower or Higher
than it should be. The “REF RANGE” tells us the normal value based on
the patient’s species, age, etc.
The first 3 values tell us that Lela is anemic. She has fewer red
blood cells (RBC) than she should. They are smaller than they should be
(MCV) but they are normal in color (MCHC.) Iron is important for making blood
cells the right color so we can probably rule out an iron deficiency.
A short but important detour: Did you know that your kidneys actually make the hormone
that signals your bone marrow to ramp up red blood cell production? Kidneys are proably the
most important organs in your body. They regulate everything from blood
pressure to blood cell production. Red blood cells are in charge of delivering
oxygen to all of the body’s cells. When you have too few red blood cells, a
condition called anemia, your organs don’t get as much oxygen as they should. When
the blood flows through the kidneys, they’re like “hold on just one damn
minute! I am not getting as much oxygen as I should. Something ain’t right
here.” Then they produce a hormone called Erythropoietin that tells the bone
marrow “hey what’s up…I’m not getting enough oxygen so I need you to make some
more red blood cells RIGHT FREAKING MEOW!”
Back to our patient. The CBC machine measured the number of baby red blood cells and indicated that there are more than there should be (Reticulocyte.) This means
that the bone marrow is spitting out red blood cells so fast that they don’t
even have time to grow up before they’re released into the blood. Based on this, we know that the kidneys are telling the bone marrow to make red blood
cells and the bone marrow is responding appropriately.
There are only two things that can lead to a situation in which we
have small, normally colored cells and lots and lots of baby red blood cells.
1. Hemorrhage: the dog has suffered some kind of trauma that is
causing it to bleed or it is slowly bleeding internally (a blood clotting problem, for example)
OR
2. The dog isn’t bleeding but there aren’t enough red
blood cells so something must be happening to them. This usually means that
the red blood cells are abnormal in some way and the spleen notices and starts killing
them because they’re weird. Maybe they have parasites attached to them.
Maybe the body’s immune system is accidentally labeling its own red blood cells
as “foreign.”
Which one is it in Lela’s case? The smoking gun is the clumping
red blood cells. This indicate that the body's immune system soldiers have decided that red blood cells are foreign and have coated them in antibodies, much like they would do with bacteria. These antibodies are tacky and cause the red blood cells to stick together. They also serve as little flags so that when the
blood is filtered through the spleen, the soldier cells in the spleen see the
antibodies and KILL KILL KILL! They actually physically
eat the tagged red blood cells or take a chunk out of them causing them to burst and die. Then all of
these broken dead red blood cells go through the liver, the organ responsible
for cleaning up the mess. This includes converting some of the compounds in the
red blood cells into a form that can be peed out. If there are too many dead
cells, the liver will be overwhelmed and some of these chemicals will spill back
out into the blood before they can be converted into the form that is peed out.
Then that blood will be circulated around and those yellowish compound give the
tissue a yellow tint. This is called jaundice.
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| Oh my gosh! Lela's gums were yellowish!! |
To summarize what we have learned from the blood work: Lela doesn’t
have enough red blood cells but her bone marrow is working hard to make more. She is
not bleeding from anywhere so the body must be inadvertently destroying its red blood cells.
Her liver is being overwhelmed with all of the cleanup, which explains her yellow gums. Lela is weak because she doesn't have enough red blood cells to supply her body with the oxygen it needs. She doesn't want to eat because she feels crappy.
We remember the hours we spent in Clinical Pathology looking at hundreds of cases and immediately know what this is.
This is a textbook presentation of Immune-Mediated Hemolytic
Anemia (IMHA.) IMHA can be caused by many different things and can happen
without warning. It just means that the body is destroying its own red blood
cells-causing an anemia, possibly a result of a drug or an infection. The good news is that this
is treatable!!!
We explain to Lela’s mom that Lela has an immune disease which can be
treated. We give Lela a blood transfusion and prescribe drugs to suppress her
immune system. Lela’s mom calls us a couple of days later to report that Lela has
perked up and is inhaling her dinner the way that she used to.
This diagnosis was made possible because of the blood work. Just
looking at Lela, we could not have known that she had an immune disease. If we
had opted for “Spray and Pray” it is very likely that Lela’s body would have
continued to destroy it’s red blood cells. Eventually her body would have given
out and she would have died due to a lack of oxygen to her vital organs.
This is why your veterinarian wants to do blood work!
This is just one example of the value of diagnostic blood work. Reaching a diagnosis often requires additional blood tests but I wanted to keep it relatively simple. The next time your pet gets sick, I hope that you feel empowered to ask your vet why he/she
is ordering a certain test. What can the results show? How will this help with
a diagnosis? You are in a relationship with your veterinarian and, as in any relationship, communication is key.
Liked what you read? Stay tuned for the next installment...Does my dog really need heartworm prevention year round?
Special thanks to the Clinical Pathologists at the UGA Teaching Hospital for providing this awesome case!
3. Lela's blood smear: http://www.eclinpath.com/ngg_tag/imha/nggallery/slideshow
4. Normal blood smear: http://www.eclinpath.com/atlas/hematology/blood-smear-features/
5. Lela's results: Clincal pathologists at the UGA College of Veterinary Medicine
6. Jaundice gums: http://www.shootinguk.co.uk/answers/my-friends-dog-went-yellow-recently-whats-bilirubin-13756
7. Happy Cocker Spaniel: http://www.spockthedog.com/breeds/medium/cocker-spaniel/
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