What Your Pet's Bloodwork Means
By Robert Skidmore, DVM
CBC (Complete Blood Count)
HCT (hematocrit) Measures the percentage of red blood cells in the blood. A low HCT is called anemia. It can be a little above the reference range due to mild or moderate dehydration. A very high HCT may indicate a fairly rare disease call polycytemia vera.
Hb and MCHC Hemoglobin (Hb) and mean corpuscular hemoglobin concentration (MCHC); hemoglobin is the substance of red blood cells that carries oxygen. MCHC is the hemoglobin concentration per red blood cell. Hemoglobin usually trends with HCT and the number of red blood cells (RBC). That is, if the HCT is low, hemoglobin is usually also low.
MCV (mean corpuscular volume) This is the average red blood cell size. May be increased if there is a regenerative anemia present.
WBC (white blood cells) White blood cells are immune system cells used to fight infection. Increases or decreases in WBC count may indicate infection and/or inflammation associated with certain diseases in the body. The total from the types of white blood cells should equal total WBC.
Types of White Blood Cells:
Neutrophils: the main infection fighter of the white blood cells; produced by the bone marrow.
Lymphocytes: consists of B and T lymphocytes derived from lymphoid stem cells in the bone marrow.
Monocytes: another specific type of white blood cell. Eosinophils: increases can be a clue of allergic or parasitic diseases.
Basophils: may play a role in anaphylaxis; increases often accompany increased eosinophils.
PLT (platelet count) A measure of the cells that are required for normal blood clotting. Very low platelet numbers (thrombocytopenia) can result in spontaneous bleeding. Too many platelets may indicate a disease called thrombocytosis and can be primary (bone marrow cancer) or secondary to other diseases.
RETICS (reticulocytes) These are immature red blood cells. Examining this number helps determine if an anemia (low HCT) is regenerative or not. A regenerative anemia is where the body is aware that the HCT is low and is actively making more red blood cells to put into circulation. A regenerative anemia is a better prognostic indicator than a non-regenerative anemia.
Blood Serum Chemistries
ALB (albumin) Albumin is the main body protein and helps determine hydration and intestinal, liver and kidney disease. If ALB gets too low edema (fluid retention and swelling) can develop. Reasons albumin may be low are either the liver is not making it or the body is losing it somewhere (through the gut or kidneys).
ALKP (alanine aminotransferase) ALKP is an indicator of liver disease or another disease called Cushing’s disease (hyperadrenocorticism). In puppies it may be elevated somewhat due to active bone growth. In Cushing’s disease ALKP is often moderately high to extremely high while other liver numbers are normal. A separate test is required to diagnose Cushing’s disease. Corticosteroid drugs like prednisone may cause an increase in ALKP.
ALT (alanine aminotransferase) This is an indicator of active liver disease/damage but does not indicate the cause. ALT is a sensitive indicator of liver (hepatic) disease, that is, if it is elevated there is liver disease of some sort present.
AMYL (amylase) Amylase is a pancreatic enzyme that is used by the body to digest food. Elevations of amylase may indicate pancreatitis. Although amylase can be mildly elevated with no other symptoms of pancreatitis.
AST (aspartate aminotransferase) AST is another liver enzyme often reported along with ALT. Taken along with other liver numbers it can help determine the type and severity of liver disease or damage.
BUN (blood urea nitrogen) BUN is an indicator of kidney (renal) function. Increased BUN may indicate acute or chronic kidney failure. It can also be elevated due to dehydration. An increased BUN is called azotemia.
Ca (calcium) An elevated calcium level is called hypercalcemia and may be caused by some cancers, kidney disease, primary hyperparathyroidism and Addison’s disease (hypoadrenocorticism). Low calcium levels is called hypocalcemia. Decreased calcium levels are not common and could be due to laboratory error. Low albumin (ALB) can make it appear calcium levels are low, but calcium may be normal when levels are corrected for low albumin levels. Diseases that may cause hypocalcemia include hypoparathyroidism, kidney failure, antifreeze toxicity, pancreatitis, eclampsia and enemas containing phosphate.
CHOL (cholesterol) Cholesterol is often elevated when there is hypothyroidism present. It may also be elevated in Cushing’s disease, diabetes mellitus and liver disease.
Cl (chloride) Chloride is an electrolyte (often reported along with potassium (K) and sodium (Na). Chloride may be elevated with dehydration and low due to vomiting and dehydration.
TCO2 (bicarbonate) This reflects the body’s acid-base balance and shows the severity of the imbalance. Some diseases that may upset acid-base balance include diabetes mellitus, Addison’s disease, kidney disease, vomiting and Cushing’s disease.
Cortisol Cortisol is a steroid hormone. Levels are checked when doing tests (ACTH stimulation test) to check for Cushing’s disease or Addison’s disease. Cortisol levels are too high in Cushing’s disease and too low with Addison’s disease.
CREA (Creatinine) Creatinine, along with BUN, is an indicator of kidney function. In kidney failure conditions, usually both the creatinine and BUN are elevated. One example of BUN being elevated but creatinine is normal is dehydration. So creatinine can help determine if an elevated BUN is due to kidney disease or something else.
CK or CPK (creatine kinase) This is an enzyme expressed by various tissues; elevations may indicate muscle damage. Sometimes confused with the kidney number creatinine.
GGT (gamma-Glutamyl Transferase): GGT is another liver enzyme like ALKP. Elevations indicate live disease. Mild elevations can be due to steroid (prednisone, dexamethasone) drugs.
GLOB (globulin) Globulin is a blood protein. Inflammatory diseases may can cause an increase.
GLU (glucose) Glucose is the level of sugar in the blood. It is increased with diabetes mellitus. Decreased glucose levels is called hypoglycemia. Causes of hypoglycemia include insulin overdose, insulin secreting tumors, anorexia in very young dogs or cats. Signs of hypoglycemia may include extreme lethargy/weakness, collapse or seizures.
K (potassium) Potassium is an electrolyte. Elevated potassium levels is hyperkalemia and can be caused by Addison’s disease, kidney disease (failure), urethral obstruction (e.g., blocked cats) and dehydration. Increased potassium levels need to be treated aggressively since it can cause heart problems (cardiac arrest). A low potassium level is called hypokalemia. Causes of low potassium levels include vomiting, diarrhea, kidney disease, diuretics (e.g., Lasix), IV fluids, some drugs and postobstructive dieresis (may occur after “unblocking” a cat that cannot urinate due to a urethral obstruction).
LIP (lipase) Lipase is a pancreatic enzyme. Increased lipase may indicate pancreatitis and may be a little more reliable than amalyse (AMYL) when trying to assess the health of the pancreas.
Na (sodium) Sodium is an electrolyte often measured along with chloride and potassium. The most common cause of low sodium (hyponatremia) is vomiting and diarrhea. Low sodium levels can also be seen with kidney disease and Addison’s disease. Common causes of high sodium levels (hypernatremia) include gastrointestinal tract or renal water loss in excess of sodium and intravenous (IV) fluid administration. Addison’s disease often has low sodium and high potassium levels.
PHOS (phosphorus) Phosphorus levels are influenced by parathyroidhormone (PTH) and Vitamin D. Interaction of these hormones with other parts of the body a ect phosphorus levels. Common causes of increased phosphorus levels (hyperphosphatemia) are kidney failure, hypoparathryoidism, excessive bone resorption, phosphate enemas, hyperthyroidism, Vitamin D toxicity and some other less common diseases. Low phosphorus levels (hypophosphatemia) could be caused by laboratory error, reduced intestinal (poor diet) or renal reabsorption, Vitamin D deficiency, and administration of the drug Mannitol (sometimes used to decrease pressure in the eye in the case of glaucoma).
TBIL (total bilirubin) Most bilirubin comes from the breakdown of heme-containing proteins (red blood cells). Elevations in total bilirubin (hyperbilirubinemia) can be due to liver/bile duct causes or hemolytic disease. In liver disease the bilirubin processing ability may be impaired so levels increase. Hemolytic disease is when the body’s red blood cells are destroyed (hemolyzed). Bilirubin is a byproduct of red blood cell breakdown and if it occurs in large enough numbers it may exceed the liver’s ability to process it resulting in increased levels. Hyperbilirubinemia with no anemia (low HCT) is likely due to liver disease. Hyperbilirubinemia with concurrent anemia and with the other liver numbers normal is probably due to red blood cell destruction by the immune system (e.g. Immune Mediated Hemolytic Anemia).
TP (total protein) Total protein can help determine hydration status as it may be elevated in a dehydrated animal. If TP levels are low either the body is losing protein somewhere (gut, kidneys) or is not making enough protein (liver disorder).
T4 (levothyroxine) Thyroxine is thyroid hormone. A low level is called hypothyroidism and is common in dogs and uncommon in cats. High levels is called hyperthyroidism which is common in middle aged to older cats. As a general rule, dogs get hypothyroidism and cats get hyperthyroidism and almost never vice versa with the exception of congenital hypothyroidism or inappropriate drug therapy (i.e., a dog may become hyperthyroid if overdosed with the drug to treat hypothyroidism). T4 levels are often all that is needed to diagnose hyperthyroidism. Dogs however may have borderline T4 levels. In this case a Free T4 should also be examined and this level typically provides a yes or no answer as to whether hypothyroidism exists in the dog. T3 levels are not a reliable indicator of thyroid disease in dogs.
FT4 (Free T4) Free T4 is a more sensitive indicator of thyroid disease. It is often run in conjunction with the T4 in dogs since the T4 may not give a firm diagnosis.