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INDEX OF ARTICLES

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LAB and PHARMACY

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The Laboratory

The laboratory is where the real detective work takes place. Often, tests on the patient's blood, urine or tissues are the final bit of evidence the veterinarian needs to close a case. Lets take a look at a typical example of how utilization of laboratory techniques can assist in making a proper diagnosis...
Muffin, a seven-year-old Collie, is presented because of a depressed appetite, increased thirst, and lack of energy. The veterinarian performs a thorough physical exam and cannot find anything overtly painful or otherwise noteworthy. Her temperature is normal although the dog seems slightly dehydrated even though she has been drinking large amounts of water. So what's going on with Muffin? She is obviously sick.  Usually the veterinarian will make a tentative diagnosis, and performing laboratory tests will either rule out the suspected disorder or add more evidence for a diagnosis. In this case there are a few systems that certainly need checking. The veterinarian suspects a kidney problem because of the increased thirst and urination (a dog can be in kidney failure and still put out large amounts of urine!) and her depressed attitude and poor appetite.

Let's check a urine sample first. If a clean catch of urine can be collected into a clean container, that is used; otherwise the dog may need to be catheterized. On any laboratory test a result is compared to an expected NORMAL value. The usual substances checked in the urine are Protein, Acidity, presence or absence of blood, bile substances, ketones, sugar and concentration of the urine. In this case the dog's urine was much more acid than normal, had a trace of blood, had a high protein content, no sugar or bile, and was high in concentration.

Right away the veterinarian can rule out diabetes mellitus since no sugar was showing up in the urine. And kidney failure is not a likely diagnosis since the urine concentration (called Specific Gravity) is higher than normal and shows that the kidneys are working hard trying to conserve water in her body. Dogs with kidney failure almost always have very unconcentrated urine (very low Specific Gravity).

So now the technician takes a small amount of urine and spins it in a centrifuge to cause the solid components of the urine to settle to the bottom of the test tube. This sediment is then examined under the microscope. Sometimes there is so much sediment that it is visible in the test tube! In Muffin's case, the technician sees large numbers of a type of white blood cell called neutrophiles, and a moderate number of red blood cells and moderate numbers of bacteria.

With this information the veterinarian is beginning to get a better picture of what isn't going on as well as what is. There appears to be an infection somewhere in the urinary or reproductive tract (Muffin has not been spayed.) Usually dogs with even substantial urinary tract infections still eat, play and drink normal amounts of water. A little more detective work is needed to decide how to help Muffin. Before a method of treatment can be designed the veterinarian must know what he is treating the dog for!

To gather a little more data on what's going on inside this dog a blood sample is taken and a few basic things are checked. For example in this case the white blood cell count, which can normally range from five to nine thousand cells per milliliter, is an amazing fifty-two thousand! Muffin really has a severe infection and interestingly does not have an elevated temperature. The red blood cell count is normal but remembering that the dog is dehydrated, the veterinarian doesn't believe this red cell count to be accurate. In fact the red cell count is falsely reflected to be normal because of the dehydrated condition of the dog and the dog is actually anemic...an important consideration if surgery is required.

Just like the urine sample, the blood sample is centrifuged and the solids (the red and white blood cells and platelets) are packed to the bottom of the test tube so that the fluid portion (the plasma or serum) can be tested. A simple test shows that the kidneys are clearing waste products from the blood but not quite efficiently enough. The test (called a BUN for blood urea nitrogen) is only slightly elevated, adding to the veterinarian's confidence that the kidneys are not the primary problem. The kidneys are simply doing the best they can and can't quite keep up with the large amount of waste and toxins being produced by the infection. The blood sugar is analyzed and it is slightly low, not surprising since the dog hasn't been eating well.

So now here is what we know:
Before the laboratory tests were done the suspicion was that the Muffin had kidney failure. Now, thanks to the detective work done in the lab, we know that she does NOT have Diabetes or kidney failure. We know that the dog DOES have a severe infection that is being responded to strongly by the dog's immune defenses. Since it is very typical of uterine infections to trigger very high white blood cell counts (fifty-two thousand certainly qualifies as very high!) the probability is that the uterus is the site of the infection. Since the uterus connects with the urinary tract, any infection and resulting pus formation in the uterus may likely pass into the vagina and be washed out in the urine. This explains all those neutrophiles (white blood cells) and red blood cells in the urine! The kidneys and bladder are actually not the source of the infection.

The veterinarian goes back to the dog and with probing fingers palpates the dog's abdomen in an attempt to feel the uterus. Muffin seems slightly tender and tenses her abdominal muscles, making a reliable abdominal exam impossible. Since the probable diagnosis is an infected uterus, called pyometra, X-rays are taken and sure enough, an abnormal density typical of an infected uterus shows upon the film! Thanks to the laboratory workup, the veterinarian was able to do a little internal exam on the dog that disproved the original suspicion and directed the search toward the actual cause of the problem.

It looks like Muffin's headed for surgery!  (But before that, learn all about The Blood Chemistry Profile)  Antibiotics won't help this kind of infection.

The Biopsy

This is a view of a very nasty cancer of an intra-abdominal lymph node.  But is it really cancer?  Maybe the lymph node is actually severely infected and just appears to be cancer.  A small section is cut from the diseased tissue (biopsy) and sent to the lab in order to have a pathologist actually look at individual cells under the microscope. All doubt was removed when the final report in this case was determined to be a spreading (metastasizing) cancer.

Many animal hospitals rely on off site laboratory help.  A good example of this is Marshfield Labs in Marshfield, Wisconsin.  This well respected human medical and surgical center also developed a Veterinary Laboratory employing a number of veterinary specialists in pathology.  The lab's Outreach Program employs carriers who pick up test specimens and transport them back to the Lab where tests are performed the same day. Results are phoned or faxed to the animal hospital the next morning.  This service is a great way for animal hospitals in a wide radius from Marshfield Labs to get specialized services from competent and experienced veterinary pathologists.  As well, Marshfield Labs receives many samples from veterinarians from all over the country that are mailed in for testing.  Capable of performing literally hundreds of different laboratory tests, from hormone level assays to platelet counts to tissue biopsy analysis, Marshfield Labs brings professional laboratory expertise to even the single practitioner working in a rural area.

One area that is extremely important for reaching a diagnosis for your pet is in the area of tissue biopsy analysis.  In these cases a sample of tissue is removed surgically or via a needle punch biopsy.  The sample is placed in special preservative solution and brought to the lab where very thin slices are made, the tissue stained with special dyes, placed on a glass slide and viewed by a pathologist.  Most commonly used to diagnose cancer, tissue biopsies are invaluable for visualizing exactly what is going on at the level of the cells.  So not only are cancer types and severity analyzed but also such disorders as degenerative diseases, allergic reactions, neuromuscular disorders, and infectious processes.  The tissue biopsy services are a modern requirement for any animal hospital.  The help of regional laboratories such as Marshfield Labs plays a very important role in providing your veterinarian with an important tool for protecting the lives of our dogs and cats.

ortunately for the veterinarian and their dog and cat patients, there are major corporations, such as the Idexx Laboratory, that have pioneered rapid and accurate diagnostic tests that the veterinarian can run right in the animal hospital. From Feline Heartworm tests to the state-of-the-art Blood Chemistry Analyzer with its multiple test menu, Idexx Labratories and companies like them have greatly assisted the veterinarian...and ultimately our pets!