There are many tests available to help your veterinarian determine presence and extent of disease. Many routine blood, urine and radiologic tests can be completed in your veterinarian’s office. Certain blood tests, such as those used to detect thyroid disease must often be sent to other laboratories. Other, more specialized tests such as CT scans or MRIs usually necessitate a visit to a major university veterinary hospital. The following descriptions are for tests that are most commonly ordered.
COMPLETE BLOOD COUNT (CBC)
RED BLOOD COUNT (RBC): Red blood cells are produced in the bone marrow under the stimulus of an enzyme produced by the kidneys. Attached to each RBC are hemoglobin molecules which give the RBC its red color and are the part of the RBC that binds oxygen. RBCs function in gaseous transport in the blood; picking up oxygen in the lungs and distributing it to all parts of the body while at the same time, collecting carbon dioxide from the cells and transporting it to the lungs to be blown off during respiration. Older or damaged RBCs are broken down by the spleen and liver. A low RBC count (anemia) could indicate: blood loss (obvious or hidden), renal disease, bone marrow failure, chronic illness, over destruction by the spleen, etc. High counts may indicate dehydration or overproduction of RBCs.
HEMOGLOBIN (Hgb): Each molecule of hemoglobin is made up of two substances, globin (a protein) and heme (an iron-containing portion). It is the heme portion which gives blood its red color and to which oxygen molecules bind. The amount of Hgb is related to the number of RBCs in the blood. Too few RBCs will mean a corresponding reduction in the amount of Hgb available. Hemoglobin is used to determine if the RBCs are normal in size and hemoglobin content.
HEMATOCRIT (Hct): The percentage of blood that is made up of RBCs. It is calculated from the RBC count and average RBC size. Abnormal values indicate the same problems that cause abnormal RBC and Hct concentrations. Packed cell volume (PCV) is a direct measurement of spun down whole blood. PCV is more accurate than Hct.
WHITE BLOOD CELL COUNT (WBC): White blood cells are also called leukocytes. There are several different leukocytes: neutrophils, lymphocytes, monocytes, eosinophils and basophils. Most are involved in destroying microbes either by dispatching them directly or by creating antibodies that render them incapable of causing disease. An increased WBC count can indicate infection, trauma, stress or inappropriate overproduction. A low WBC count can indicate bone marrow failure, overwhelming infection or auto-immune disease. By determining the various individual WBC types (differential count), it is possible to further determine the probability of infection or inflammation and whether the cause is bacterial, viral, parasitic, stress-induced, etc.
PLATELET COUNT: Platelets are small cells that respond rapidly to injuries that cause bleeding. They act, together with clotting factors produced by the liver, to seal off ruptured blood vessels by creating clots. Their ability to bind to injured vessels is mediated by von Willebrand’s factor. Low platelet counts indicate a number of clinical disorders that can be reflected by abnormal bleeding. These include immune-mediated disorders, bone marrow problems and several tick-borne infections. High platelet counts are uncommon.
SERUM CHEMISTRY TESTS
ELECTROLYTES: These include sodium, potassium, calcium, magnesium, chloride, bicarbonate and phosphate. Each of these is essential to cell metabolism and is maintained in a narrow range in the healthy dog. A severe alteration in any one these can disrupt cellular activity and, if extreme, lead to cell destruction. An electrolyte imbalance can be caused by inadequate dietary or water intake or a breakdown in the body’s balancing mechanisms. They often result from vomiting, diarrhea, and kidney, respiratory or endocrine disease.
GLUCOSE: Glucose is a sugar needed by all cells for energy production. The level of glucose in the blood is regulated by the interaction of several hormones including cortisone, and insulin and glucagon which are produced by the pancreas. Insulin must be present for most cell membranes to “open up” and allow glucose to enter. An underproduction of insulin by the pancreas means that glucose cannot enter the cells; instead it accumulates in the bloodstream and the condition known as diabetes mellitus ensues. Too much glucose in the blood causes detrimental changes to blood vessels, nerves, eyes, liver and kidneys. Other causes for high blood glucose include: Cushing’s disease, hyperthyroidism, adenoma of the pancreas, pancreatitis, diuretics and corticosteroid therapy. Too little glucose in the blood can be due to starvation, hypothyroidism, overexertion, AddisonÕs disease, pancreatic islet cell tumors, severe bacterial infection or extensive liver disease. In puppies there also is an enzyme deficiency that they outgrow (juvenile hypoglycemia).
BLOOD UREA NITROGEN (BUN): Body proteins are constantly being created and taken apart largely by the liver. When proteins are broken down, an end-product called urea is formed from ammonia and carbon dioxide. Urea is usually eliminated from the body by the kidneys. An elevation of the BUN can indicate dehydration, kidney disease, obstruction to urine outflow, low blood flow to the kidneys, high protein diet, bleeding into the bowel, or conditions that cause protein breakdown such as fever, infection, or trauma. A decrease in BUN levels can indicate overhydration, liver failure or insufficient protein intake.
CREATININE: This is an end-product of skeletal muscle breakdown and is also excreted by the kidneys. An elevated creatinine level indicates dehydration, kidney disease, lack of appropriate blood flow to the kidneys or obstruction to urine outflow.
AMYLASE: Amylase is an enzyme produced by the pancreas and released into the small intestine. It acts to break down carbohydrates during digestion. An elevated amylase level may mean that a problem with the pancreas is present which can include inflammation, tumor, obstruction, or leakage. Amylase is excreted in the urine and thus may be elevated by many of the same causes as increased BUN and creatinine.
LIPASE: This is another enzyme produced by the pancreas. It acts to breakdown fats during the digestive process. An elevated lipase level can indicate pancreatitis or other pancreatic disorders, including pancreatic carcinoma. It also is excreted by the kidneys.
ALANINE AMINOTRANSFERASE (ALT): This is an enzyme produced by the liver that increases in amount when liver cell damage is present. An increase can indicate liver inflammation, liver necrosis due to toxins, portosystemic shunt or cancer.
ALKALINE PHOSPHATASE (AP or ALP): An enzyme found in many tissues (liver, bone, intestine, kidney and placenta). Only that from the liver and bone last long enough in the blood to be measured. In the liver it is present in the edges (membranes) of liver cells and the cells of the small ducts that carry bile to the gall bladder. It does not leak into the blood with damage to liver cells like ALT (see above). Many drugs especially cortisones and anti-convulsants cause the liver to make another form (isoenzyme) of AP. Some laboratories can separate bone from liver AP and liver AP from the drug-induced isoenzyme. Bone AP is increased in growing dogs and in some bone diseases including certain tumors. Liver AP is increased when there is decreased or blocked bile flow either within the liver or outside of it. This increase can occur before jaundice is seen. It is important to separate liver AP from the induced AP since so many cortisone family drugs are used in dogs (prednisolone, prednisone, dexamethasone, triamcinolone to name a few) and the occurrence of naturally occurring high cortisone levels in Cushing’s disease and prolonged stress. AP is also present in colostrum. Pups that have nursed colostrum will have very high levels for about 10 days.
GAMMA-GLUTAMYLTRANSFERASE (GGT): This enzyme is similar to AP but is found mostly in the liver and kidney. Serum GGT is of liver origin as kidney GGT goes out in the urine. It is not produced by bone. It is considered to be more liver-specific than AP. GGT rises in bile stasis like AP and can also be increased by cortisone-like drugs. Colostrum contains high levels of GGT. Newborn pups who have nursed colostrum will have very high GGT values in their blood for several days.
BLOOD AMMONIA: An elevated blood ammonia level indicates liver disease.
BILIRUBIN: As old or damaged red blood cells are broken down, bilirubin is released, removed from the bloodstream by the liver and excreted in the feces. If too much remains in the bloodstream, it can give a yellowish color to skin and eyes (jaundice). An elevated bilirubin can indicate hemolytic anemia (too rapid breakdown of RBCs), liver disease or obstruction of the bile duct.
SERUM PROTEINS ( ALBUMIN & GLOBULINS): Albumin is produced by the liver. Albumin serves to help regulate blood volume and blood pressure. Globulins are antibody proteins. They are made by the liver and lymphoid tissues. A decrease in the amount of these proteins in the blood can indicate a reduction in protein production due to intestinal malabsorption, malnutrition or liver disease. A decrease in protein can also indicate an increase in protein loss due to kidney or intestinal disease or chronic blood loss. An increase in protein levels can indicate shock, dehydration or infection.
This is a screening test for abnormalities of the kidneys and lower urinary tract. It detects the following characteristics and constituents of urine:
pH: Indicates the acidity of the urine. The kidneys play an important role in maintaining a correct body acid-base balance. It is affected by diet and many drugs. It must be measured from fresh urine.
Specific Gravity: Measures the concentration of particles in the urine. A high specific gravity indicates concentrated urine and a low specific gravity indicates dilute urine. It is affected by hydration and many drugs as well as kidney disease.
Color and Clarity: Normal urine is clear. Cloudiness can indicate infection. Color is affected by blood, bile, drugs (including vitamins) and other substances. Normal urine is pale yellow. Concentration (high specific gravity) may cause a deeper yellow coloration.
Protein: Normally not present. If present, can indicate renal disease or infection/bleeding anywhere in the urinary tract.
Blood: Normally not present. Presence of blood can be due to infection, renal stones, trauma or a tumor in the urinary tract.
Glucose: Normally not present. If present, can indicate a high blood sugar due to diabetes, kidney disease or the patient has recently eaten.
White Blood Cells: Normally not present. Presence can indicate infection or inflammation in the urinary tract. It can also be affected by the method of urine collection.
Ketones: Normally not present. Ketones in the urine can indicate diabetes, starvation or an abnormally low carbohydrate diet.
Crystals: Microscopic mineral particles of many different kinds. Presence affected by diet, pH, drugs, specific gravity and disease.
Casts: Cylindrical clumps of material derived from red blood cells, white blood cells or cells from the kidney itself. They require protein and an acid pH to form.
Bacteria: Not normally present. Presence can indicate urinary tract infection, depending on the method of sample collection and the interval between collection and analysis.
This is usually performed after a routine urinalysis is abnormal or other signs (e.g. incontinence) exist. A urine culture requires as sterile a specimen as possible; that is, one that is not contaminated by the bacteria that normally inhabit the area around the urinary meatus (the opening through which the urine leaves the body). To do this, your veterinarian may insert a flexible tube (catheter) through the meatus and urethra and into the bladder. Another technique is to insert a sterile needle directly into the bladder through the lower abdominal wall(cystocentesis)and withdraw a specimen into a syringe. This is the preferred method. A urine culture provides valuable information on the type of bacteria present and which antibiotics it will be most susceptible to.
A chest x-ray is performed to determine the presence of lung, cardiac or esophageal disease. Several views with the dog in different positions may be necessary although the standard is one side-to-side and one bottom-to-top.
COMPUTERIZED AXIAL TOMOGRAPHY (CT/CAT)
An x-ray technique that produces cross-sectional images of the inside of the body. Useful in detecting soft-tissue and some bony abnormalities. Anesthesia is required.
MAGNETIC RESONANCE IMAGING (MRI)
The MRI scanner produces a magnetic field that causes the nuclei of cells to line up in a uniform manner at which time, radio frequency pulses are applied causing these nuclei to resonate and emit energy signals which are converted via computer into images. An MRI image can provide clearer differentiation of certain tissues than a CT image. However, the process takes longer than a CT scan and it is less available due to its higher expense. Also, the presence of any iron-containing metal precludes the use of MRI since the metal can become dislodged from its usual site. All metallic objects locally disrupt the magnetic field induced during an MRI causing a distortion of the desired image and making diagnosis impractical. For instance, a dog with a prosthetic joint containing ferrous (iron) metal could not have an MRI. Anesthesia is required.
Sound waves are used to produce images of internal organs and to identify abnormalities. These waves pass best through liquid and worst through air. Most procedures require shaving to bare skin. Anesthesia is not required.
Rigid or flexible tubes are inserted into various areas of the body to visualize internal structures. Within the tubes are lighting and magnification devices. Devices can also be inserted through the tube to allow for the collection of tissue specimens for culture, cytology or biopsy. Anesthesia or heavy sedation is required.
Electrodes are placed on the legs and chest to detect the electrical impulses produced by different locations within the heart. These are translated into a tracing that provides information about the heart’s rate and rhythm. Used to diagnose irregularities of the heart and to monitor the heart of critically ill dogs.
CYTOLOGIC EVALUATION (CYTOLOGY)
A microscopic examination of a tissue or fluid specimen that has been fixed onto a glass slide and stained to enhance cellular detail. The tissue or fluid is often collected by means of aspiration with a fine-gauge needle attached to a syringe inserted into a questionable lump or swelling. This test is done to identify inflammatory or infected lesions, benign cysts and cancers.
Surgical or cutting needle biopsy of a tissue or organ that ultimately provides a thin section which is fixed ontoa glass slide, stained and examined under a microscope. This gives more information than a cytologic evaluation.
SEROLOGIC TESTING (SEROLOGY)
The detection of antibodies to or parts of bacteria, viruses, parasites, etc. in the serum or plasma.
Samples of cells or tissues are collected for microscopic examination. An excisional biopsy would remove the entire lesion and possibly an area of surrounding normal tissue. An incisional biopsy would be a specimen collected from part of a lesion or tumor. Needle biopsies are incisional. The sample is placed in a fixative and further processed (see Histopathology). A frozen-section biopsy is a method of rapid tumor identification while the dog remains under general anesthesia. This equipment is not commonly available and requires the presence of a pathologist during surgery.
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