“Blood Work” what is it … and what is it good for?
In short; blood work is a snapshot of how the body is functioning inside. It is highly dependent on age, species, breed, medication etc. It can be useful for screening, monitoring, planning etc if in the hands of an experienced practicioner. In my (Dr. Childs) experience it is more useful if the pet owner knows why we are performing such tests and what the results mean. So if you want some light reading I made this for you! 🙂
Just like in people, testing the blood is one of the best ways of determining ongoing internal health and is an essential part of screening, monitoring, and ongoing health assessments.
Blood circulates through the entire body and blood cells are replaced on a monthly bases and are thus a good way at assessing health, especially those aspects that cannot be detected on a physical exam.
There are several types of blood tests available, and each individual will require different types of testing depending on many factors (including, age, breed, health status, anticipated procedures, medications, pregnancy etc). The types of tests available often change and there are far more available than we will discuss here. If you have any questions at all please feel free to give us a call or email as Dr. Childs would be happy to talk with you further about your options and the current state of laboratory testing.
Despite the fact that blood work is notoriously dependent on individual factors such as age, breed, meds etc, there are some things that are rather standard and if you have the patience would be worth learning about and understanding.
Basic blood work typically consists of 2 samples:
1 – complete blood count (CBC)
2 – biochemistry (Chem)
These samples are taken from the vein, just like you would get done if you were donating blood or getting a blood test, except that we take less than 3 millilitres of blood.
The blood is then sent to a laboratory (which lab your vet uses will depend on their location, company etc). There are Bord-certified Veterinary Patholologists (Veterinary school (4 years) + a residency (4+years)) so they know their stuff!) who analyze each sample under a microscope and also with various high tech machines to get as much information out of each sample.
Complete Blood Count (CBC)
The CBC checks the number, type, health and other characteristics of red blood cells, platelets and other circulating cells.
CBC may be useful as a screening test for underlying infection, anemia and illness.
Sometimes, the CBC can help determine the underlying cause of an anemia or infection. Drugs that affect the bone marrow change the CBC. Certain types of cancers, especially leukemia, may be evident on a blood smear. Blood parasites and some microorganisms are found by careful inspection of the blood cells during the CBC. In some cases, the results of the CBC will prompt your veterinarian to recommend other diagnostic tests.
- WBC is an abbreviation for white blood cell count. These cells help fight infection and respond when an area of the body becomes inflamed. Elevated white blood cell counts indicate infection, inflammation and some forms of cancer or leukemia. Low white blood cells counts can indicate viral infections, bone marrow abnormalities or overwhelming infections and sepsis (blood poisoning). In this situation, the white blood cells are concentrated in the area of infection and are not circulating in the blood, resulting in a low count.
- RBC is an abbreviation for red blood cell count. These cells are responsible for transporting oxygen throughout the body. Oxygen is used as fuel for the body and is very important. High red blood cell numbers usually indicate dehydration but can also indicate uncommon diseases that cause an excess production of red blood cells from the bone marrow. Low red blood cell counts are referred to as anemia and can be a result of blood loss, active bleeding, bone marrow disease or excessive red blood cell breakdown that is seen in some immune diseases and toxin ingestion.
- HGB is an abbreviation for hemoglobin. This molecule is responsible for binding and releasing oxygen onto the red blood cells. Without hemoglobin, oxygen cannot be transported. High levels of hemoglobin usually indicate high red blood cell counts and dehydration. Low levels indicate anemia, bleeding or iron deficiency.
- HCT is an abbreviation for hematocrit. The hematocrit is a calculated percentage of red blood cells in the circulation. It gives similar information to the red blood cell count but the value is expressed as a percentage. The other part of the blood is serum, containing enzymes, proteins, electrolytes, etc. High hematocrits indicate dehydration or rare bone marrow disorders resulting in increased red blood cell production. Low hematocrits indicate anemia, bone marrow disorders, blood loss, active bleeding or excessive red blood destruction due to toxins or immune disorders.
- MCV is an abbreviation for mean corpuscular volume. This is the average size of the red blood cells. A high MCV usually indicated certain vitamin deficiencies. A low MCV indicated iron deficiency.
- MCH is an abbreviation for mean corpuscular hemoglobin. This is the average weight of hemoglobin in each red blood cell and is different than hemoglobin circulating in the blood. A high MCH indicates poorly oxygenated blood. A low MCH indicates iron deficiency.
- MCHC is an abbreviation for mean corpuscular hemoglobin concentration. This is the average percentage of hemoglobin in each red blood cell. A high MCHC indicates that there is too much hemoglobin in the red blood cell, indicating a high iron level since an important component of hemoglobin is iron. Iron excess is just as damaging to the body as iron deficiency. A low MCHC indicates anemia.
- PLT is an abbreviation for platelets. The platelets are responsible for sealing any leaks in the blood vessels. When platelet counts are low, spontaneous bleeding can occur. High platelet counts usually indicate a disorder of the bone marrow or an overwhelming response to an immune blood disease. Low platelet counts indicate bleeding or excessive destruction of platelets caused by parasites or immune diseases.
- A differential is an analysis of the different types of white blood cells. There are five types of white blood cells and the distribution of these cells can help determine an underlying cause of illness.
- Segs is an abbreviation for segmental neutrophils. These are the primary white blood cells responsible for fighting infections. High levels of neutrophils indicate infection. Low levels can indicate sepsis. The neutrophils are concentrated in the area of infection or are rapidly being used, leaving less circulating in the blood.
- Lymphs is an abbreviation for lymphocytes. These white blood cells are also responsible for fighting infection and also develop antibodies to protect the body against future attacks. High levels of lymphocytes can indicate infection, viral disease or certain cancers such as lymphosarcoma. Low levels can indicate viral infections affecting the bone marrow or sepsis.
- Mono is an abbreviation for monocytes. This white blood cell helps the neutrophils fight infections. High monocyte counts indicate infection. It is unlikely that there will be no monocytes and a differential with zero monocytes does not indicate any specific ailment.
- Eos is an abbreviation for eosinophil. This white blood cell is primarily involved in fighting allergies or parasites. High eosinophil counts indicate an allergy or parasite causing illness. Low levels are not possible since zero eosinophils are possible in normal blood samples.
- Baso is an abbreviation for basophils. This white blood cell is not very common but can be seen in certain parasitic infection, primarily heartworm. High levels indicate possible parasitism. Low levels are not possible since zero basophils are possible in normal blood samples.
The Biochemical Profile
A biochemical profile is a blood test that assesses the function of internal organs, measures the electrolytes such as blood potassium, and identifies the levels of circulating enzymes. Understanding the biochemical profile can be difficult but reveals a wealth of information.
Components of the biochemical profile:
Glucose is the end product of carbohydrate metabolism and is the primary source of energy for the body. High levels indicate stress, Cushing’s disease, diabetes, pancreatitis or can be due to certain medications. Low levels can indicate liver disease, insulin overdose, severe bacterial infection, hypothyroidism and Addison’s disease. Toy breed puppies are prone to low blood glucose for unknown reasons.
BUN stands for blood urea nitrogen and is the primary end product of protein metabolism. High levels indicate kidney failure or disease, dehydration, shock, high protein diet, certain toxin ingestions, poor circulation to the kidneys and urinary obstruction. Low levels indicate liver disease or starvation.
Creatinine is the end product of phosphocreatine metabolism, which is important in muscle contractions. High levels indicate kidney failure or disease, dehydration, shock, certain toxin ingestions, poor circulation to the kidneys and urinary obstruction. Low levels indicate liver disease or starvation.
Sodium works in combination with potassium and is very important in maintaining normal function of muscle and nerves. It is also an important electrolyte in every part of the body. High levels indicate dehydration, lack of water, diabetes insipidus, Cushing’s and excess salt intake. Low levels indicate starvation, severe diarrhea, vomiting, Addison’s disease, hypothyroidism and metabolic acidosis.
Potassium works in combination with sodium and is very important in maintaining normal function of muscle and nerves. High levels indicate diabetes, certain toxin ingestions, urinary obstruction, acute kidney failure, severe muscle damage and Addison’s disease. Low levels indicate vomiting and diarrhea, gastrointestinal cancer, insulin overdose, Cushing’s disease, overuse of diuretics and starvation.
Chloride is important in maintaining the acid balance in the blood as well as combining with hydrogen to form hydrochloric acid for stomach digestion. High levels indicate dehydration, metabolic acidosis, Addison’s disease and kidney disease. Low levels indicate vomiting and metabolic alkalosis.
CO2 indicates the current acid balance of the body and is the end product of metabolism. High levels indicate an acidic condition and can be due to kidney failure, vomiting, dehydration or overuse of diuretics. Low levels indicate a basic condition of the blood and can be due to starvation, kidney failure (can also cause acidosis), diarrhea and poor liver function.
Calcium is a mineral found throughout the body. It is the basis for bones, teeth and muscle contractions. High levels indicate certain forms of cancer, Addison’s disease, excess intake of vitamin D and an overactive parathyroid gland. Low levels indicate eclampsia, severe pancreatitis, dietary imbalance, intestinal absorption disorders, low intact of vitamin D, Cushing’s disease and certain toxin ingestions.
Phosphorus is often associated with calcium. It is important in all aspects of metabolism. High levels indicate kidney disease, dietary imbalance, excess ingestion of vitamin D and severe tissue trauma. Low levels indicate dietary imbalance, certain cancers, overdose of insulin, diabetes, eclampsia and an overactive parathyroid gland.
Total Protein (TP) is an important substance in all parts of the body. High levels indicate dehydration, inflammation, chronic infection and certain cancers. Low levels indicate intestinal absorption problems, liver disease, Addison’s disease, severe burns and losses through the kidneys.
Albumin is the major protein found in the body. It carries various substances through the blood and is important in maintaining pressure within the vessels. High levels indicate dehydration. Low levels indicate chronic inflammation, liver disease, kidney disease, starvation and blood loss.
Bilirubin is a bile pigment and is the end product of red blood cell breakdown. High levels typically result in jaundice and can be due to bile duct obstruction, gall bladder obstruction, liver disease and rapid breakdown of red blood cells. Low levels are not considered clinically relevant.
Cholesterol is important in the synthesis of certain hormones. High levels are not as important as in people. Low levels indicate liver disease, starvation, kidney disease, Cushing’s, pancreatitis, diabetes and hypothyroidism.
Triglyceride is important in storing fat and releasing fatty acids. High levels have been associated with seizures in schnauzers. Low levels indicate starvation or malnutrition.
ALKP is important in metabolism and is found in liver cells. High levels indicate bile duct obstruction, Cushing’s, liver disease, certain cancers and may be due to certain drugs such as steroids or phenobarbital. Low levels indicate starvation or malnutrition.
AST is important in the breakdown and elimination of nitrogen. High levels indicate muscle damage, heart muscle damage, liver damage, toxin ingestion, inflammation and various metabolic disorders. Low levels indicate starvation or malnutrition.
ALT is also important in the metabolism of nitrogen and is most often associated with the liver. High levels indicate liver damage, toxin ingestion, Cushing’s disease and various metabolic disorders. Low levels indicate starvation or malnutrition.
GGT is also important in nitrogen metabolism and is found within liver cells. High levels indicate bile duct obstruction, liver disease, pancreatitis, Cushing’s and can be caused by high levels of steroids. Low levels indicate starvation and malnutrition.
Amylase is secreted by the pancreas and is important in normal digestion of starch. High levels indicate pancreatic inflammation or cancer, kidney disease, prostatic inflammation, diabetic ketoacidosis and liver cancer. Low levels can indicate malnutrition or starvation.
CK is very important in storing energy needed for muscle contractions. High levels indicate muscle trauma or damage such as due to seizures, surgery, bruises, inflammation, nutritional and degenerative diseases. Low levels are not clinically relevant.
thyroid hormone: Dogs and cats have circulating thyroid hormone levels that are important for everyday cellular function (see more in my thyroid posts in resources (link coming soon!)). Put simply, the thyroid gland secretes thyroid hormone and different issues (illness, autoimmune disease,cancer, medication, etc) can cause the thyroid gland to produce too much or too little thyroid hormone. This is detected in blood work (in the biochemistry portion).
Again, the blood test taken today is only a snapshot of the today. Your pets individual health, medical record, current and past medications, and anticipated procedures, and many other factors, are going to be very important in determining the type of tests appropriate and the interpretation of the resutls.
Furthermore, there are certain combinations of tests and monitoring intervals (repeated or additional testing) that may be recommended depending on various factors.
I find it much more rewarding when pet owners understand a bit more about the testing, why we do it, why certain tests are valuable in certain circumstances, what the results mean, and what future tests may be necessary. I hope this post helps, but it IS a very complex topic that is frequently changing and I welcome you to ask about anything that is unclear (or perhaps simply interesting) to you at your next appointment. I am always happy to try to explain things with respect to your pets unique situation.
Dr. Helene Childs