Kitty recently had a blood test? Are you wondering about the results? Can't make sense of the various abbreviations and what they actually mean?
We have some answers for you.
Written by veterinarian Letrisa Miller, DVM, this article goes over the various elements of a blood panel in cats, aka a complete blood count or CBC.
Before we walk through the alphabet soup of blood test results, a word of caution. Interpreting blood test results on your own isn't wise.
As Dr. Miller explains, a qualified veterinarian has many considerations when reading a feline blood panel. That's why we avoided providing actual numbers for most of these tests. Doing so could be misleading. You could end up fretting over nothing, or worse, falling into a false sense of security that could delay treatment for your cat.
And now, we hand the virtual mic over to Dr. Miller.
Can Cat Owners Interpret Blood Test Results on Their Own?
Interpretation of the results within the right context is important. Hematology - the study of the blood's composition - has a lot of nuances that can make interpretation difficult.
- Blood collection methods
These nuances start with the tube of blood that is collected. The type of anticoagulant that is used can make a big difference, and how much blood is put into the tube can as well. Doctors have to know how to interpret the results in light of many variables relating to collection and storage of samples as well as methods of determining values.
- Result Ranges Used By Lab
What the normal range in one laboratory is may not necessarily be what the normal range is in another laboratory.
- The effect of stress on the cat
In veterinary patients, and in particular cats, there are often changes that are associated with the stress a cat feels from travel and being in an unfamiliar environment that can affect the numbers and types of cells found in the blood.
- The cat's level of hydration
Results have to be interpreted very carefully as well with consideration of the cat’s hydration. If a cat is dehydrated, the blood will be concentrated so the packed cell volume or hematocrit will be higher even though it is really an artifact of the dehydration, and when normal amounts of water are restored to the body, the numbers may change a great deal.
- The cat's age
Age can make a difference in what the normal ranges are. That goes for kittens as well as senior cats.
Cat blood test results explained
RBC: Red Blood Cells
RBC (mil/uL) stands for the concentration of red blood cells in millions per microliter of whole blood. This is a measurement made by a machine that counts cells.
HGB shows the hemoglobin concentration of whole blood. It's an indicator of how much hemoglobin is present, thus a crude measurement of how much oxygen can be carried by blood.
HCT provides an estimate of red blood cells as a percent of the total volume of blood. A normal value for a healthy adult cat is approximately 30% to 45%, but normals vary according to what method is used and the individual laboratory. This is the measurement used most often to determine anemia.
Mean Corpuscular Volume & Hemoglobin
MCV= Mean Corpuscular Volume: The volume that the average red blood cell occupies.
MCH=Mean Corpuscular Hemoglobin: How much hemoglobin is in the average red blood cell in picograms.
MCHC=Mean Corpuscular Hemoglobin Concentration: How much hemoglobin is in the average red blood cell in terms of volume.
MCV and MCHC are primarily used in interpreting anemias. They help to guide a clinician in identifying if a cat is making new blood cells as it should be when anemic. Cats that are chronically ill often will have what is called a non-regenerative anemia where the bone marrow is not able to make red blood cells fast enough to replace those being lost to old age. In these cases, both of these numbers tend to be normal.
When there is blood loss, there should be more new red blood cells present as the bone marrow starts to make new red blood cells to replace the lost ones. New red blood cells are larger than older ones so they have a higher MCV. If there is considerable blood loss, the bone marrow may not be able to produce hemoglobin as fast as it produces new red blood cells, and then hemoglobin concentrations go down. Because of this the red blood cell volume and hemoglobin concentration help the doctor figure out why there is anemia.
WBC: White Blood Cells
WBC (K/uL) stands for concentration of white blood cells in thousands per microliter of whole blood. This measurement can be done with a machine or by hand on a microscope with an instrument called a hemocytometer.
Total white blood cell counts are used most often to determine if there is infection, inflammation or (sometimes) cancer present, but very often it is difficult to tell which one might be causing an increase or decrease of white blood cells. Very acute infections or inflammation can cause low white blood cell counts or high ones, depending on the particular individual and the body’s response.
Chemotherapy is often toxic to the bone marrow, and so CBCs are used frequently to monitor the health of the bone marrow in these patients.
The types of white blood cells present give lots of clues as to what may be causing a disease process. Cats often also have changes in what types of white blood cells are present due to stress-induced release of adrenalin. This process causes abnormalities in a pattern called a stress leukogram that has to be recognized by the clinician as due to stress, not disease. This physiological reaction to stress can also mask abnormalities.
The white blood cell differential is actually more important in most of the cases that I see than the red blood cell values. I need to know how many of each type of white blood cell are present. Neutrophils, mature and immature, can tell me a lot about infection and inflammation. Eosinophils tell me if there could be a problem related to allergy or parasites. Monocytes and basophils can tell me if there is likely to be a disease like lymphoma or inflammatory bowel disease.
PLT (m/uL) stands for concentration of platelets in millions per microliter of whole blood. This is a measurement made by machine in almost all cases. For cats, this measurement is almost always wrong because cats’ platelets clump when blood is drawn, and machines can’t count clumps.
Blood Test Procedures in Cats
Blood collection in cats can be done in many ways. In our clinic, we believe that there should be nothing done with a cat that we are not comfortable with our clients seeing, so we draw blood in the exam rooms. Most of the time we use a vein on one of the front legs in cooperative cats.
I can often draw blood from a cat with no restraint other than my holding the leg with one hand while I draw blood with the other. If the cat is fidgety, a nurse will hold the leg for me and I will use one hand to hold the paw while drawing blood with the other.
Some cats are better suited to drawing blood from the inside of a back leg. This is a better location for cats that are declawed, because of atrophy of the front legs from the loss of toe function, or cats that have arthritis in the front legs. Some cats that have arthritis in all limbs or do not like to be touched except on the head will have blood drawn from the jugular vein in the neck. The jugular vein draw is what is taught in most veterinary schools.
I, personally, won’t use the jugular vein in a cat that we can’t hold still because I don’t want to have the cat move in a way that could cause damage to the throat.
We don’t use sedation to draw blood unless a cat will not tolerate any restraint of any type. It is unusual to have to do this if fear-free methods are used unless it is a cat that cannot be touched without sedation.
Getting the Results
We do most of our hematology (CBC) in our clinic, and it takes about 20 minutes. We do not measure hemoglobin in our laboratory, rather we look at the red blood cells on slides and look at the color of the red blood cells as was done before the automated machines were available. The mechanized cell counters have a difficult time with cat blood and return errors that indicate a blood smear needs to be looked at in order to determine accurate data.
Because of this I have not purchased an expensive machine and have taught my technicians to interpret what they see on microscope slides. When people look at a lot of blood smears, they get good at recognizing abnormalities in the cells and can actually get a lot more information than from a mechanized count. It just doesn’t generate numbers for red blood cell size and hemoglobin concentration, rather, changes are indicated by mild, moderate or marked. If we need the numbers for hemoglobin, we will send the blood out to a reference laboratory.
When cell counts are done by machine, whole blood is examined by a cell counter and it determines what type of cell is going through a laser and what size it is. When platelet clumping is present, which happens in about 95% of cats, the machine cannot determine platelet numbers and a slide has to be looked at to see if adequate numbers are present. Most “in house” machines also cannot consistently accurately determine what types of white blood cells are present in cat blood, although the technology keeps getting more accurate every year.
Changes that machines absolutely cannot see are whether or not neutrophils have toxic changes or if there are inclusions in any of the white blood cells or red blood cells. Toxic changes are most commonly seen with infection, and the presence of toxic changes in neutrophils is very useful in determining if a cat has a bacterial infection vs inflammation.
Inclusions or membrane changes in red blood cells that cannot be seen with machine counts can also add a huge amount of information.
Cats are prone to getting a type of anemia from toxin exposure called Heinz body anemia from damage to the red blood cell membranes. Heinz bodies are easily seen on blood smears.
Some infections are also best diagnosed by looking at white blood cells or red blood cells under the microscope. The most common of these is a mycoplasma infection of the red blood cells called feline infectious anemia. Many practitioners now use a PCR test to diagnose this disease, but looking at a slide on a microscope can give a much faster diagnosis that can be confirmed by the PCR test that takes longer to send to a reference lab and get results.
Changes in the shapes of red blood cells can also point to liver diseases and other disease processes.
If the CBC is sent to an outside reference laboratory, results are usually received the next day. The majority of the extra time is due to transportation of the blood to the laboratory. The advantage of sending the blood to one of these laboratories is the expertise associated with having someone who only does lab work looking at the samples.
Vets generally use CBC information in sick cats, although looking for anemia in cats that appear healthy can help catch chronic diseases earlier in some cases. It is a very useful tool in getting a better idea of the whole picture of how the body is functioning and what could be causing an illness.
Dr. Miller is a founding fellow of the International Association of Cat Doctors and served as president in 2012 and 2013. She is also a member of the American Veterinary Medical Association, the Connecticut Veterinary Medical Association, the International Society of Feline Medicine, and the Veterinary Information Network. From 2006 through 2011 Dr. Miller was a board member of the American Association of Feline Practitioners AAFP) and for several years she was the chair of the AAFP's research committee. In 2010 she represented the AAFP at the founding of the Cat Health Network, a collaboration among the American Veterinary Medical Foundation, Morris Animal Foundation, Winn Feline Foundation, and AAFP to fund and promote research in feline medicine.You can read more about Dr. Letrisa Miller on her website.