At The Laboratory With Your Pet's Doctor

In this ongoing series of columns on laboratory tests, we will look at individual tests or tests commonly grouped together to see why a doctor might choose them for a patient.

If you've ever experienced a serious, debilitating illness, your first stop after leaving the doctor's office was probably at the lab. Or, you may have been hospitalized and the doctor may have had the lab come to you, to your hospital bedside.

When you get to the lab, how does the technician know what tests to perform? The doctor has defined what is called a "minimum database". This is comprised of a set of tests that will provide the doctor with enough information to get him on the right track to either confirming a diagnosis he already suspects, or, if he's not yet sure which of a number of ailments might be your main problem, tests to narrow down the possibilities.

Depending on factors called "signalment", which include gender, age, height, weight, hair color and race, a minimum database for a young person with a mild illness might include CBC (complete blood count), chemistry profile and urinalysis. Today, let's learn more about the CBC.. In later columns we will investigate in depth additional common tests that are used.

CBC is a universally used term to refer to the complete blood count. It is complete because it examines all of the blood cells circulating in the body. It is a count because results report the number of each different kind of cell found by the laboratory technician.

First, let's look at red blood cells (RBCs). They are the most numerous cells in the bloodstream, and have the main duty of carrying oxygen and nutrients to all of the parts of the body, in addition to many other important functions. If a patient has too few of them, he is called "anemic". Anemia has many forms and many causes. The simplest is blood loss anemia, though sometimes the doctor's challenge is finding out where the blood is being lost! An obvious cause would be blood spilled from a wound in an auto accident. A less obvious cause would be gastrointestinal (GI) loss from stomach ulcers or parasites such as hookworms.

Other forms of anemia are caused by failure of the body to make new red blood cells as rapidly as old ones die or are used up. Many causes exist here, as well, including iron deficiency, bone marrow problems, chronic kidney disease and deficiencies of microminerals.

Now let's look at the other class of blood cells examined in a CBC: the white blood cells (WBCs). A common one is the Neutrophil, which comes in mature (segmented) and immature (band) forms. Presence of excessive numbers of these in circulation is usually associated with a source of inflammation, sometimes infection, but possibly from other sources of irritation in which infection is not a factor.

The next most numerous WBC in the normal patient is the Lymphocyte. Lymphocytes are cells produced by the immune system and primarily function in fighting illnesses, including cancer, viral disease, bacterial infections, fungal infections inside the body, etc. Numbers of these are increased in certain diseases as the body makes more to keep itself healthy, and decreased when the body is under such great stress that it can't make enough or when that stress results in the release of large amounts of a natural hormone called "cortisol". Lymphocytes are also increased in very large numbers in the cancerous disease "leukemia".

Eosinophils are WBCs that are usually associated with allergic and hypersensitivity reactions. Some allergic patients can have extremely high numbers of these.

Basophils and monocytes are WBCs that play a part in inflammatory conditions. Rarely do they reach great numbers in circulation.

In future editions of "At The Laboratory With Your Pet's Doctor" we will take a close look at the chemistry profile, urinalysis, thyroid screening tests, fungal assays, electrocardiograms, X-rays and more. Watch this space every week.

"At The Laboratory With Your Pet's Doctor, Part Two"

In the last edition of "At The Laboratory With Your Pet's Doctor", we studied the details of the Complete Blood Count. Today, we will look at a battery of tests called the "Chemistry Profile".

In the Complete Blood Count, we were examining physical bodies, tiny little cells that circulate in the bloodstream. With the Chemistry Profile, we're learning about the things in the bloodstream at the molecular level, truly the metabolic function of the body.

You've probably heard the doctors on ER or other hospital shows call for a "Chem 7". This is a tiny little panel of chemistry tests that tells us only about 7 parameters. What the laboratory we use calls a "SuperChemistry Profile" includes 26 parameters. Let's look at them one by one.

Two tests tell us about how much waste products the kidneys are (or are not) removing from the blood. BUN, or Blood Urea Nitrogen, measures nitrogen molecules broken off from protein molecules we've eaten. This nitrogen has to be removed from the blood as a waste item, or it becomes toxic.

Likewise, creatinine is a waste item produced by muscles that is removed by the kidneys. Together, the results of these two measurements tells us whether waste that is supposed to be removed by the kidneys is being removed from the blood quickly enough.

Now let's look at liver tests. Routine screening tests do not test the function, or capacity of the liver to do its job. All they do is to tell us whether the liver has been damaged. First, let's look at ALT, and important liver enzyme. Enzymes, by the way, are ingredients that help a chemical function to occur. If your pet's doctor finds that the chemistry profile is showing him that the ALT is elevated, he knows that the liver has been damaged and is leaking the enzyme. The damage could have been physical, such as a car accident, or chemical, such as a poison that killed part of the liver, releasing the enzyme. How high the number goes can, but doesn't always, tell us how bad the damage is, and a very high number doesn't necessarily mean that the situation is hopeless.

Likewise, a low ALT doesn't mean that everything in the liver is rosy. Remember we said that none of these tests tell us how well the liver is (begin italics) functioning (close italics)? A classic example is that of a patient with cirrhosis of the liver, or a liver which has been poorly supplied with blood circulation for a long time. These are examples of livers which will function poorly, but whose ALT level will likely be normal, because the liver isn't leaking the enzyme.

Are you starting to understand why it's not always clear-cut when the doctor can't tell you exactly what's wrong, even though he's run a lot of tests?

Other test results in a broad-based chemistry panel that will tell us about the liver include SGOT, Alkaline Phosphatase (SAP) and bilirubin. Unfortunately, there isne' space to go into detail about each of these.

Now let's look at another broad category of the Chemistry Panel: the Electrolytes. Electrolytes include Sodium, Potassium, Chloride, Phosphorous, Calcium, Magnesium, Bicarbonate and Sulfate. Most of those look familiar, don't they? Most of them are in your Gatorade, aren't they?

Electrolytes have the important job of maintaining normal function of cells in the body. It's how nerve cells conduct electricity to perform functions from movements to thoughts. It's how kidney cells remove waste products from the bloodstream. It's how liver cells detoxify some of the awful things we ingest.

There are two main things that have to be right about electrolytes: they can't be too high or too low, and they have to maintain the right relationship to each other. For example, if calcium goes up, and phosphorous doesn't go up with it (within limits), there can be serious, even fatal consequences. If calcium goes up, and phosphorous goes down, a whole different set of consequences comes into play.

"If a little bit is good, then a whole lot is better" definitely doesn't play with electrolytes.

"At The Laboratory With Your Pet's Doctor, Part Three"

In our ongoing series about how and why your pet's doctor chooses laboratory tests, and what the results mean, we continue our look at the Chemistry Profile.

Glucose. Everybody knows glucose. It's also known as blood sugar. Problems can occur when it's too high or too low. Rarely is low glucose, hypoglycemia, a problem in adult animals, though it can be deadly in kittens and puppies.

Hyperglycemia, or elevated blood sugar, on the other hand, is not uncommon, and is our best indicator to confirm clinical suspicions of diabetes mellitus, the most common form of diabetes in man and animals. As with people, diabetes is a very treatable condition.

Cholesterol. Everybody knows cholesterol. While cholesterol usually doesn't cause plaque and obstructions in arteries as it does in people, it can be a good indicator of other problems, such as low thyroid function and an growing problem in pets: lipemia.

Lipemia is the presence of fats in the bloodstream that are present in excessive amounts. Pets with this problem can usually be controlled with a low fat diet, but some may need cholesterol-lowering drugs. Failure to control the lipemia can lead to seizures and inflammation of the pancreas, a digestive organ that also produces insulin.

Inflammation of the pancreas is a fairly common presentation, and most commonly occurs when a pet has gotten into fatty foods he wasn't supposed to have access to, such as from the garbage can. Two enzymes are used to measure damage to the pancreas. Lipase is a pancreas-specific enzyme, while Amylase is produced by the pancreas and the digestive tract. The pancreas can be very inflamed, even fatally inflamed, without either of these enzymes being elevated beyond normal ranges.

Protein measurement is an important part of the chemistry panel. Albumin is an important protein that is produced by the liver. Low albumin levels can be caused by failure of the liver to produce enough, or it may be caused by loss of albumin through the intestines or kidneys or both. Low albumin levels can lead to osmotic balance problems in the blood, as well as failure to carry adequate calcium in the bloodstream. High albumin levels occur in dehydration and, rarely, in cases of overproduction of the protein.

Another important protein measured in the chemistry panel is globulin. Globulin is actually a combination of several proteins, and is an indicator of activity in the immune system.

Bilirubin is commonly a measurement made in chemistry profiles. It can be a measure of a liver's ability to perform a usual daily liver function. Bilirubin will also be elevated when bile is unable to flow out of the liver and into the intestinal tract through the bile ducts. In that condition, a liver enzyme, Alkaline Phosphatase (mentioned above) will usually also be elevated.

Next time in "At The Laboratory With Your Pet's Doctor", we'll look into the urinalysis and culture of the urine.

Stay tuned, every week!

"At The Laboratory With Your Pet's Doctor, Part Four"

In an ongoing series, Your Pet's Doctor has informed you about laboratory tests your pet is likely to have performed as routine screening tests, as preoperative tests, and as tests designed to diagnose illness.

Today we're going to look at tests commonly performed on urine.

The most basic is urinalysis, which is performed in two parts. First, let's start with the chemical parts of the urinalysis. These are usually performed with a dipstick, so-called because it is dipped into a urine sample to begin the testing process. A dipstick is a strip of plastic with paper squares attached, onto which have been added certain chemicals which can detect components in the urine both normal and abnormal. The amount of each urine component is indicated by the amount of color change on the square. The color on the strip is compared to colors on the chart to determine the test result.

Let's start at the top of the dipstick and work down.

pH is the first test square. The pH of the urine tells us how much acid is present or absent. Most dogs' and cats' urine should be a pH of 7.0 (neutral) or less (meaning more acid). A high pH may indicate a recent high-carbohydrate meal, an abnormality in metabolism that is causing the urine (and possibly even the blood) to have a pH that's too high, and in some cases can indicate urinary tract infection caused by bacteria that are splitting nitrogen molecules, thus creating base, the opposite of acid. So far, we've looked at only one square, and we already have a lot of information.

Color change in the next test square indicates the presence of blood in the urine. The presence of blood in the urine is always abnormal. If there is enough blood in your pet's urine that you can see red with the naked eye, you should call your pet's doctor right away. A positive test for blood may result from infection, physical trauma to the urinary tract (such as a blow from a car or a blunt object), bleeding growths or stones in the bladder. Sometimes tiny blood vessels are damaged in the process of obtaining the urine sample. If the amount of blood is very small, the clinician may take that possibility into account.

A test square to indicate protein in the urine is very important, because several kinds of urinary tract disease "spill" protein into the urine. Infections in the bladder may damage blood vessels, releasing protein from the blood, infections and other diseases may damage the kidneys themselves, causing loss of protein. Anything more than the tiniest amount of protein in the urine is considered abnormal. Some inherited diseases of the kidneys that occur in certain breeds of dogs and cats will first be detected in the very young animal by testing the urine for protein.

Never should there be glucose (sugar) in the urine of a normal patient. Under certain circumstances a diabetic patient may be allowed to have glucose in the urine temporarily, but even then not for long periods of time. The presence of glucose in the urine may mean kidney damage is allowing glucose to be "spilled" into the urine. It can also mean that blood levels of glucose are excessively high, as occurs in diabetes mellitus. Extreme excitement or short-term stress can also elevate blood glucose, especially in the cat.

Related to diabetes mellitus and glucose metabolism is the ketone test square. The presence of ketones in the urine is always abnormal, and represents an abnormality is glucose metabolism. Ketonuria is a condition most commonly seen in poorly regulated diabetics.

Urobilinogen and Bilirubin are tests to help differentiate liver disease from destruction of red blood cells in the bloodstream.

A refractometer is used to determine urine specific gravity (SG). Here's an easy way to understand SG: Fill a drinking glass with water, and add a heaping tablespoon of mud. At this point, the specific gravity of the contents of the glass (muddy water) is pretty low, meaning you have a little mud in a lot of water.

Now, take that glass outside and leave it in the hot sun for a couple of days. As the water evaporates, and the mud stays behind, the contents of the glass gets thicker and thicker. That means that the specific gravity is going up. And, so it is with urine specific gravity.

When you're watching the Super Bowl with a room full of your friends, and you're drinking glass after glass of iced tea, the body tells the kidneys to get rid of the excess fluid you're taking in, while continuing to rid the body of the usual amount of waste products. Thus, the urine specific gravity is quite low (lots of water, not much mud).

Alternatively, if you're in the desert with no canteen, your body still has to get rid of the waste products it's producing, but there's no excess of water to spare. So, the kidneys form urine that has all the waste in a very small amount of urine, a high specific gravity. When your pet's doctor asks you to withhold water from your pet before testing, he's simulating those desert conditions, forcing the kidneys to "do their best". How they perform on the specific gravity test tells the doctor a lot about your pet's kidney health.

Next comes the microscopic portion of the urinalysis. This part is harder, and more time-consuming, but both parts must be performed if the doctor is to have a complete picture of the patient's urinary tract and metabolic health.

The microscopic portion of the urinalysis can be performed either or both of two ways: stained, or unstained. No, we're not talking about spilling the urine on the veterinarian's clothing, we're talking about applying stain to a thin layer of wet urine on a microscope slide. Some like it plain, some like it stained. There are advantages both ways and often a single specimen will be evaluated both ways.

On this part of the test we're looking for cells, mostly. Normal cells that line the bladder are called transitional epithelium. Like any other cell in the body, they can become cancerous, so we're keeping a sharp eye out for cancer cells under the microscope.

Sometimes bacteria can be seen. Normal urine is sterile, meaning that there are no microorganisms present. Therefore, if bacteria are seen, the immediate meaning is that the urinary tract is infected. Often the presence of bacteria will stimulate the doctor to order a culture of the urine. The purpose of a culture is to grow, identify and further refine the nature of the infection. We will discuss cultures in detail in a future edition of the Your Pet's Doctor In The Laboratory series.

Another common finding under the microscope is the presence of casts. Granular casts are formed as cells or proteins take on the shape of the architecture of the interior of the kidneys. Seeing a few is normal, seeing a lot of them can indicate a serious problem.

Crystals are important when seen under the microscope. Sometimes they are indicators of stones, or there may be small numbers of crystals in a patient who hasn't yet formed a stone, but the crystals tell the clinician that the patient is predisposed to forming stones. This early indicator may allow the doctor to change the patient's diet, thus preventing a bigger complicating factor.

Some crystals mean worse news than others. For example, seeing crystals of ethylene glycol, antifreeze, usually means that the patient is in a lot of trouble.

Parasites. When you think of parasites, you usually don't think of the urinary tract. However, there are parasites that live there, and the microscopic portion of the urinalysis is one of the best and least invasive ways to identify their presence.

The single most important thing to understand about urinalysis, chemical and microscopic, is that it's not just about the urine and the urinary tract. Tests performed on the urine tell us much information about the function of the body as a whole. April 10, 2003

"At The Laboratory With Your Pet's Doctor, Part Five"

Here we are back in the laboratory with your pet's doctor. Today we'll be discussing the test called bacterial culture and sensitivity.

As the name implies, it's a two-part test: The culture part of the test tells you that something is going to be grown. In fact, laboratory technicians will take the specimen the doctor sends in and attempt to grow any and all bacteria present in the specimen.

"Now, how in the world do they do that?", you might ask. It is truly part of the best testing that modern medicine has to offer.

Let's assume that the specimen we're trying to grow bacteria from is a urine specimen. The doctor collects the specimen from the patient in a sterile fashion, meaning he does his best not to allow any contamination from other parts of the patient's body, from his own hands or from surfaces such as the table the patient is sitting on. A urine specimen is usually collected into a sealed tube or bottle.

When the container arrives at the lab, the lab technician is also careful not to contaminate the specimen as she opens it and transfers it to a culturing device. A tube-shaped device is made up of several sections which contain different foods and conditions for bacteria to grow in. Down through the middle of the tube the sample is introduced, inoculating each section. Different types of bacteria will grow in each different section and what-grows-where, and the effect the growing bacteria have on the medium in which they're growing actually tells the technician what kind of bacteria is causing the patient's infection!

All bacteria have names, so when the test is finished, the technician can call your pet's doctor and tell him what the name of the infection is, and, almost as important, whether there are a lot or a few of them.

At this point, the test is only half finished. The sensitivity portion of the test remains to be performed. But, if the doctor has begun a medication for infection of the urinary tract, and now, armed with the information that the infection is being caused by such-and-such bacteria, he can change the medication if necessary while he awaits the sensitivity test.

The first step in the sensitivity test is to obtain some of the bacteria that grew in the culture. Now, feed them well, put a light on them, keep them warm and allow them to grow again.

Now that she has a good stock of the bacteria causing the infection in our patient, the technician will subject those bacteria she so carefully grew to antibiotics to try to kill them. All of this is done in a single Petri dish with antibiotic sensitivity discs. These are small pieces of special paper, about the size your hole puncher makes, saturated with a known amount of antibiotic. Ten or so discs are placed in each Petri dish. The choice of antibiotic discs is based on previous knowledge of what antibiotics usually kill the bacteria identified in the culture step.

In a few days, the technician will examine the dish for zones of inhibition. The size of the area of dead bacteria around the antibiotic disc tells us which antibiotics are working and how well. Now, a report in generated and faxed to the clinician so that he can choose an antibiotic known to kill the bacterial infection in his patient.

What good is this? Before bacterial culture and sensitivity, all a doctor could do for a known infection is say, "Let's try this medicine and see if it works." If it didn't he tried another medicine, hoping it would work. If it didn't, he kept trying medicines until he hit on the right one.

Wow, sounds like a perfect test, doesn't it? Are there any drawbacks? Well, yes.

One, it's labor-intensive and uses high technology devices. That means it isn't cheap. And if the culture yields two or more types of bacteria, there is a charge for each sensitivity that follows the identification. Ear infections may grow three or more organisms, and that extra cost adds up.

Two, sometimes your pet's doctor takes a specimen, handles it carefully, sends it to the lab and it doesn't grow. Some bacteria are just so fastidious that they won't grow in an artificial environment, but that doesn't keep them from growing in your pet's body! Likewise, urine cultures in our feline patients can be frustrating because of a natural ingredient that cats' urine contains that prevents bacterial growth. Again, it may not keep the infection from growing in your pet, but the infection may die at the lab before it can be identified.

It is also important to understand that a specimen for bacterial culture and sensitivity is different from a biopsy specimen and testing. And that's the topic for our next trip to the laboratory.

"At The Laboratory With Your Pet's Doctor, Part Six"

Biopsy.

It's a scary word, isn't it?

But it doesn't have to be, because a biopsy can just as easily bring good news as bad.

First, let's define biopsy: "The removal and examination of tissue, cells or fluid from the living body."

So, though we may usually think of a biopsy in terms of taking all or part of a solid tumor, there are other forms of biopsy as well.

FINE NEEDLE ASPIRATE---One of the least invasive and best-tolerated procedures to help diagnose a condition in a patient involving a mass, swelling or fluid collection is the Fine Needle Aspirate. To perform it, your pet's doctor will usually use a big syringe wite a small needle. After clipping the hair from the area to be biopsied, and preparing it as one would for surgery, the needle is inserted into the suspicious area, a big vacuum is pulled with the big syringe. If everything goes right, fluid or cells enter the needle (and the syringe, too, if there's enough of it and it's free-flowing). The material is now spread on a microscope slide so that the clinician can send it to a pathologist. The pathologist will stain the slide with special stains that allow him to see the details of the cells/fluid/material in hopes of making a diagnosis.

Potential drawbacks of the fine needle aspirate are:

>a growth may not consist of a cell type that "gives up" or exfoliates cells easily. Therefore the material removed may not contain diagnostic characteristics.

>because the needle is entering a very small part of a bigger problem area, a tiny needle may miss the most important information. For example, some cancerous tumors may have normal tissue inside them. If the needle happens to enter normal tissue, even though it's immediately adjacent to cancerous tissue, the result may be a misdiagnosis of normalcy.

That said, a fine needle aspirate is easy, inexpensive and relatively painless. If it gives the practitioner the answers he seeks, it's great. If it doesn't, it is still easy to go further to more aggressive biopsies.

TISSUE BIOPSY: Tissue biopsy is usually thought of as removing the entirety of a mass and submitting it to a pathologist for study. In some cases the mass may be too large to remove completely, and a portion is submitted for the purpose of making a diagnosis. Then, if the diagnosis is grave, more aggressive treatment may be chosen.

An example might be a large mass on an extremity. If the pathologist returns a non-cancerous verdict, the mass might be handled conservatively, such as debulking. Debulking involves removing a large portion of a mass when the entire mass cannot be removed. On the other hand, if the verdict is that the growth is likely to spread and endanger the health of the entire patient, removal of the limb might be indicated (please see www.AnimalGeneralHospital.com . Click on the link for Archived Columns and read the column on amputation success stories.)

So, your veterinarian has removed tissue from your pet. What happens to it next? When it arrives at the pathologist's office, a technician will take the entire growth from its formaldehyde-filled container and place it in a histiotome, a device to slice thin portions of the growth. Those thin slices are then affixed to a microscope slide and subjected to specially-colored stains that bring out the characteristics of the tissue that help the pathologist make a diagnosis. Using a microscope that can achieve very, very high magnification, the pathology doctor will examine the tissue's most detailed points to come to a conclusion about the nature of the growth.

Notice I said, "come to a conclusion." Tissue samples don't come with little signs that say, "I'm a malignant melanoma," or, "my diagnosis is..." Pathology is a very advanced science in the practice of medicine, but, like so many other diseases, many cancers look alike, even in the fine details under a microscope. Sometimes a judgement call has to be made as to the type of cancer observed. Sometimes the pathologist will give us a list of possibilities, from most to least likely.

FLUID ANALYSIS: Recall that the definition of "biopsy" includes the removal and analysis of fluids from the body as well as tissue. Examples include diseases of the chest cavity in which there is pus, transudate, modified transudate, exudate, lymph or chyle. In the abdomen, fluid collection caused by heart disease is called ascites. A traumatic encounter with a car might call for analysis of abdominal fluid to determine whether the urinary bladder has ruptured.

Sometimes fluid from a mass can give clues as to a diagnosis of the rest of the mass, and what treatments might be appropriate for the mass.

The pathologist is our friend. He is an invaluable member of your pet's doctor's health care team, and his renderings on cytologies, histopathologies and fluid analyses can help chart the course for your beloved pet's successful treatment.