Compared with other leukocytes, lymphocytes are long-lived and are capable of mitosis and/or transformation to more functionally active forms. Most are short-lived (about 2 weeks); however, others, such as memory cells, may live for years. Lymphocytes are also unique because they recircumate from the lymph systems to the blood and back. Recirculation promotes antigen stimulation of naïve lymphocytes.
The number of circulating lymphocytes tends to be be quite constant in health and decreases slightly with age. Epinephrine release from excitement can cause lymphocytosis. Lymphocytosis can be caused by antigenic stimulation; however, this does not correlate well with enlarged lymph nodes in acute stages of infection. During chronic infections, lymphocytes may increase dramatically, particularly in rickettsial type infections. Lymphocytosis may also occur with lymphocytic leukemia or lymphoma.
Increases in eosinophils are generally associated with parasitic infection or hypersensitivity. Parasites may be ectoparasites such as fleas or endoparasites such as roundworms or heartworms. Hypersensitivity may be immediate or delayed and include asthma, dermatitis or gastroenteritis. Eosinophilia may also occur with various neoplasms such as mast cell tumors and with some bacterial, viral and fungal infections as well as in drug reactions and hypoadrenocorticism.
Urea is synthesized by hepatocytes via the urea cycle, which is one method of incorporating NH4+ into molecules for excertion of excess NH4+ formed in tissues or the intestine. Urea is filtered by kidney glomeruli and is excreted in urine or resorbed by renal tubules. Fifty to sixty percent of urea present in glomerular filtrate is resorbed in proximal tubules and collecting ducts. Urea resorption in proximal tubules is enhanced by H2O resorption and by increased ADH activity. Urea enters the intestinal tract by blood or the biliary system where it is degraded by enteric bacteria and passively absorbed into portal blood, or excreted in feces.
Elevations in BUN may be caused by diseases that decrease urinay excretion of urea before the urea gets to the kidney, such as hypovolemia and decreased cardiac output. Decreased urinary excretion may also occur from renal diseases such as glomerulonephritis, pyelonephritis, amyloidosis, toxic nephrosis (i.e. hypercalcemia, myoglobin, ethylene glycol), and congenital hypoplasia. Post renal conditions include urinary tract obstruction or leakage into the abdomen or tissues of urine from the urinary tract. BUN elevations may also be caused by increased production of urea from intestinal hemorrhage or increased protein catabolism.
The ALP measurement is actually a family of enyzmes that are associated or attached to cell membranes. Many cell membranes have ALP activity but only a few produce enough ALP to increase serum ALP activity. One form of ALP (C-ALP) is a unique canine enzyme that is produced by hepatocytes when stimluated by corticosteroids. ALP enzymes are inducible by other drugs and hormones than corticosteroids, these include phenobarbital, and thyroxine. Young growing animals have elevated serum ALP and other causes of increased bone growth, such as increased growth hormone, can cause elevations. Bone damage, including neoplasia and fractures, can also cause elevated ALP.
Cholestasis, intrahepatic or posthepatic, can also cause elevations in ALP. These types of diseases include degenerative conditions causing hepatocyte swelling or necrosis; metabolic diseases such as lipidosis, hyperadrenocorticism or diabetes mellitus; neoplastic condition such as lymphoma, pancreatic or bile duct carcinoma; inflammatory conditions such as pancreatitis or cholangitis and toxic conditions. Many older dogs have ALP elevations, but the underlying cause is never identified.
RBC’s in urine may have many different appearances depending on the concentration of the urine. They will appear shruken in concentrated urine and will balloon or even rupture in dilute urine. More than 5 RBC’s/HPF indicates hemorrhage which may be traumatic or inflammatory in nature.
WBC’s in urine are usually neutrophils and appear round and granular. They are larger than RBC’s and smaller than epithelial cells. They may lyse in dilute or alkaline urine. More than 5 leukocytes/HPF indicates urogenital tract inflammation that may or may not be septic. Leukocytes are frequently associated with bacteruria, but significant bacteruria can occur without pyuria.
Decreased appetite +/- weight loss
Rule-outs for these problems include diet change, oral pain, medications, environmental stress, metabolic and endocrine diseases, gastrointestinal disease, pancreatitis, hepatic and renal disease. Neoplasia may also cause these signs.
Lethargy is a vague clinical sign that can be caused by many different things. These include primary CNS disease, cardiovascular disease, endocrine & metabolic diseases and neoplasia.
Occasional vomiting & soft stools
These signs can be caused by many different things. These include metabolic & endocrine disease, exocrine pancreatic insufficiency, gastrointestinal disease, diet change and environmental stress.