A serum chemistry panel is a conglomeration of tests for various chemical
substances that are common in the blood stream. Whole blood, which contains
red blood cells, white blood cells and plasma is allowed to clot in a tube
and then spun in a centrifuge to separate the cells from the liquid portion
of the blood. The liquid portion is the serum. The quantity of different
enzymes, proteins, sugars and other chemicals in the serum can tell a great
deal about how well the pet's body is functioning. The most common of these
tests will be discussed in this article and then in the coming months we'll
detail how these tests are grouped and combined with other tests to evaluate
the function of specific organs, such as the kidney and liver.
Blood glucose is checked on almost every chemistry panel. High blood
glucose (hyperglycemia) usually occurs when diabetes mellitus is present.
In a dog, blood sugar levels much above normal are almost always diagnostic
of diabetes mellitus. Normal blood sugar levels for a dog are between 60
and 115mg/dl. Normal blood sugar for an unexcited cat is between 70 and
125 gm/dl. Unfortunately, it is hard to draw blood and have an unexcited
cat patient at the same time. Cats can elevate their blood sugar substantially
in response to stress so it is important to evaluate hyperglycemia in cats
with that fact in mind. A stressed out cat may have a blood sugar value
of 180 gm/dl or more. The cat is just making sure it has enough sugar in
its blood to fuel its "fright or flight" response adequately. It isn't
a good idea to give a cat insulin for diabetes based on one blood sample
taken when the cat has to be peeled off the ceiling to get the sample.
Low blood sugar is also important. The brain of most mammals is strictly
dependent on sugar to function. When the blood sugar level is low enough
that there isn't enough sugar available for the brain to function a kitten
or puppy may faint, may develop seizures or possibly even die. Hypoglycemia
occurs sometimes in toy and small breed puppies even after they are several
months old due to problems with sugar storage or utilization in the liver.
It is important to remember that this is a possible problem when seizures
occur in young small breed dogs.
The total protein level in the blood stream is an important variable
that is usually checked in general chemistry panels, as well. There are
a number of different types of protein circulating in the blood stream
at any time but they generally fall into two major categories, albumin
and immunoglobulins. While the total protein level can be used to screen
for problems, its main use is to help in determining the levels of the
albumin and immunoglobulin. If there is some question about whether blood
loss has been chronic or if it has occurred acutely, the protein level
can help in the determination. When a bleeding episode occurs protein is
lost along with red blood cells. When anemia occurs without blood loss
the protein level tends to be normal despite the anemia.
Albumin is the workhorse protein. It helps to maintain the body's osmotic
balance, keeping the fluid portion of the blood inside the circulatory
system by providing the osmotic "pull" towards the inside of the veins
and arteries. It serves as a transport vehicle for some medications and
other molecules necessary for survival. Low albumin levels occur when the
body is not making enough albumin, not absorbing enough protein from the
digestive tract or when it is not being conserved properly due to organ
damage. The liver makes albumin. There has to be significant liver damage
for albumin levels to drop, though. The kidneys work to conserve albumin
and keep it from being excreted in the urine. When they are not working
properly albumin can be lost. Blood vessels are normally impervious to
albumin, keeping it on the inside of the vessel. Significant inflammation
of the blood vessels can allow albumin to leak and be lost from the circulation.
Starvation or inadequate protein in the diet can lead to low albumin levels.
Intestinal disorders which make it hard for the intestine to absorb nutrients
can also eventually lead to low protein levels in the bloodstream. Albumin
is determined directly by lab testing. Subtracting the albumin level from
the total protein level gives a good estimate of the quantity of immunoglobulin
in the blood stream since it is the other major protein component of the
blood. Immunoglobulin levels vary pretty widely but very high or very low
levels can indicate immune system disease or indicate that infections may
be chronic rather than acute. Feline infectious peritonitis often causes
very high immunoglobulin levels in the bloodstream and this is one hint
that this disease, which is hard to diagnose with certainty, is present.
Blood urea nitrogen (BUN), which is sometimes referred to now as serum
urea nitrogen (SUN) is an indicator of how well the kidneys are functioning.
The kidneys keep the BUN levels within normal limits when they are able
to function normally. In cases of dehydration the BUN level may rise above
normal even though the kidneys would be functioning normally if there was
sufficient volume of circulating blood. Usually BUN levels rarely exceed
70 without some actual kidney damage, though. While the increased urea
nitrogen level in the bloodstream is an indication of problems, the urea
nitrogen itself is not harmful to the pet. It just rises in concert with
other toxins in the blood stream that are a problem. Most dogs and cats
are reluctant to eat when the BUN is above 100 or so. BUN rises quickly
when the kidneys are damaged so it is an earlier indication of problems
than the creatinine level, another test related to kidney function. Creatinine
levels are normally 0.5 to 1.6 in cats, with slightly higher normals in
dogs. The creatinine level is a good indicator of chronic renal damage
and accumulative kidney damage. The BUN and creatinine levels are both
monitored to measure the success of treatments aimed at helping the kidneys
to function. To give you some idea of why these lab values are compared
when kidney failure is suspected consider two patients; one has a BUN of
130 and a creatinine of 2.6, the other has a BUN of 90 and a creatinine
of 5.5. Which patient probably has acute kidney failure? The one with the
BUN of 130 and Creatinine of 2.6. The high BUN indicates a pretty severe
problem but the lower rise in creatinine level indicates that the damage
probably came on quickly rather than being a chronic problem. Even though
its BUN is lower the other cat may actually be in more trouble.
Alkaline phosphatase and alaminotransferase (ALT) are two liver enzymes
that are also usually compared in tandem, although both values have meaning
on their own. The alkaline phosphatase (ALK PHOS, ALKP) level rises when
there is an obstruction to bile flow. It is not solely a liver enzyme and
can rise for reasons unrelated to the liver, such as bone damage, bone
cancer and muscle damage. Most of the time increases in the ALK PHOS occur
because of disorders that are affecting the liver, though. This particular
enzyme frequently rises due to the influence of drugs on the liver. Corticosteroids
such as prednisone frequently cause the ALK PHOS level to rise. Phenobarbital
can do this. It is not unusual to see ALK PHOS levels as high as 350 U/L
when cortisones or phenobarbital are being given to a patient. We used
to see astronomical rises in the ALK PHOS when we used caparsolate for
heartworm treatments. I can remember dogs with alkaline phosphatase levels
over 15,000 who recovered uneventfully after heartworm treatment. It is
possible to have rises in alkaline phosphatase without having corresponding
rises in the other liver enzymes. It is very important to rule out interference
from a medication being administered to a pet as a cause of the rises in
ALK PHOS when evaluating the significance of rises in this liver enzyme.
Alanine transferase ( ALT, sometimes still referred to as SGPT for serum
glutamic pyruvic transaminase ), is an enzyme produced inside liver cells.
It is released from the cells when they are injured or when they die, so
it is an indication of direct damage to the liver. This is a pretty specific
enzyme for liver damage in dogs and cats. Rises in ALT can be pretty high,
sometimes 10 to 15 times normal levels, but any rise should be considered
to be important enough to monitor. This is especially true in cats. ALT
is also sensitive to administration of a number of medications, including
all of the ones that affect ALK PHOS and several antibiotics. It is therefore
important to consider medication administration as a potential factor when
ALT levels rise, too.
Calcium levels are usually included in most larger screening panels.
Seizures can occur when calcium levels are too high or too low. Calcium
is necessary for proper functioning of nerve cells and muscles. When levels
get below 8 or above 12 there are usually problems. High calcium levels
occur when there is metastatic cancer, particularly lymphomas. Low calcium
levels are most commonly associated with "milk fever" or eclampsia, which
is a disorder of seizuring and tremoring that occurs in the first few days
after a bitch delivers puppies.
Potassium is an important electrolyte in the serum. It moves in conjunction
with sodium but the potassium levels tend to vary more when disturbance
in electrolyte balance occur. Potassium is important in the control of
muscle function. Low potassium levels are common in cats with kidney disease
and if they get low enough the cat will have a hard time moving. Problems
due to low potassium levels are sometimes mistaken for arthritis in older
cats. Vomiting and gastrointestinal disease can cause potassium loss as
well. High potassium levels are life threatening. Hypoadrenocorticism (Addison’s
disease) is one cause of high potassium levels. When potassium levels get
high enough they interfere with regulation of the heart muscles and lead
to cardiac arrest. While it is sometimes necessary to have both the sodium
and potassium levels in order to discern the cause of potassium changes
screening panels often provide only the potassium level. Further testing
is often necessary when this value is abnormal.
What does it mean when the blood chemistry values are all within normal
limits but the pet is obviously very ill? Infectious illnesses affecting
the organs for which lab values have little meaning, such as the lungs,
heart, intestines, bladder, etc. will cause little disturbance in serum
chemistry values, although they often affect the complete blood cell count
to a greater degree. Cancer can be very severe without disturbing serum
chemistry values. Sometimes this is just an indication that more specific
testing has to be undertaken or that additional , less common serum chemistry
tests must be run. The need for further testing can often be determined
by the history of the illness and the results of a physical examination.
Even in these cases knowing that the serum chemistry values are normal
can be very helpful, even if it doesn’t provide a diagnosis.
What does it mean when the lab results are not normal but the patient
appears to be completely normal? This situation is much harder for veterinarians
to evaluate, especially early in their careers. A veterinarian who is not
highly confident in his or her diagnostic skills is highly likely to believe
that the lab values have more meaning than their physical exam. Veterinarians
who are overly confident in their physical exam skills may ignore a lab
value because it doesn't fit with the diagnosis they would like to make.
Laboratories make mistakes. In a large panel there is actually a reasonably
good chance of an error on one of the tests. Medications administered to
the pet may cause false lab values. Falsely high glucose measurements have
been observed when cephalexin is administered, for instance. Handling of
the blood sample can affect the results. Even the patient's condition can
have an effect on the blood samples. Hemolysis of the blood, lipemia (fat
globules in the blood stream) or icterus (yellow discoloration of serum
that occurs with liver disease or hemolysis) can affect the results of
some tests. It is important to evaluate the patient carefully and to correlate
the findings of the exam with the labwork. Sometimes the labwork looks
really bad but the patient is healing. This is particularly true of high
ALT and alkaline phosphatase levels in a patient recovering from an acute
insult to the liver. It is important to remember that lab values, while
generally reliable, have to be considered to be just one part of the diagnostic
picture. Even though there is an expense involved, it is often better to
recheck lab values when they seem odd, rather than just dismissing them
or making too much of them.
When should screening lab panels be run in normal pets? There are times
when it is probably a good idea to consider a screening chemistry panel
even when a pet does not seem to be ill. Prior to elective surgeries many
veterinarians are much more comfortable if they have run a blood chemistry
panel to rule out hidden illnesses. It is not a bad idea to consider having
blood chemistries evaluated a couple of times during the lifetime of a
pet, just to have baseline values for that pet or to begin to screen out
disorders associated with aging, such as chronic renal failure in cats.
While there isn’t a general agreement on when it is best to consider routine
screening of blood chemistry values other than prior to surgery, I think
that it is reasonable to consider doing this at five or six years of age
and then periodically as pets gets older.
Pets Traveling by Air
During the time I have been in practice a number of my patients have
been flown on airplanes, either in the passenger compartment or in the
cargo holds. When it is possible it is obviously better to take a pet on
board in the passenger compartment. Their carrier must fit under the seat,
though. This limits this choice to very small dogs and cats, usually. When
pets must fly in the cargo hold it is worrisome for their owners. Many
pet owners want to sedate dogs that must travel by air but this may be
a very bad idea. In a review by the USDA and the airlines of pet deaths
that occurred during airline flights the most common cause of death was
sedation. The two main reasons cited for this were oversedation and unpredictable
effects of sedation associated with high altitudes. Most cargo holds are
pressurized to at the equivalent of 8000 feet or so. It appears that sedatives
exert a stronger effect at high altitudes. In addition, many owners appear
to oversedate their pets, probably because the sedatives may not appear
to be working while the dog is excited during the process of preparing
to fly due to the car rides, being confined in an unfamiliar crate and
the separation from family members. The temptation to give an additional
sedative during this time is very high. Once the pet is in the cargo hold
and settles down the effect of the sedatives becomes more obvious but no
one is there to monitor the pet. The second most common cause of death
was environmental stress -- temperatures that are too hot or too cold.
It is often inconvenient to arrange shipping around the daily temperature
but it is important to avoid airplane trips in the middle of the day in
summer or even to consider a trip when the temperature is staying about
85 degrees most of the day. Pets are usually OK once the plane is off the
ground but a one hour delay sitting on a hot runway without air-conditioning
can be fatal for a pet confined in the cargo hold. The third most common
cause of death was acute illness from diseases that were not apparent at
the time of the mandatory health exam prior to flight. Diseases like parvovirus
have an incubation period in which they are inapparent. If the patient
is incubating a disease but showing no clinical signs when the exam for
the health certificate is done the disease may manifest itself during the
flight. Having an acute illness during a flight is dangerous to the pet’s
health. The least common cause of death was accidents attributable to handling
errors. These do occur. I have seen a dog crate fall out of an airplane’s
cargo hold at O’Hare Airport while I was traveling and these sort of accidents
are inevitable if enough pets are shipped in airplanes. Fortunately, they
seem to be rare occurrences. I don’t know if it really has any effect but
several of my clients decorate the crates with signs that say the crate
contains a really nice dog or cat whose owners love it very much and one
even has several photos of their dog on the crate, just in case it does
get loose and to reinforce the notion that it is a special pet.
It seems apparent that sedation should be reserved for pets that really
need it and that when it is necessary the directions for dosing the sedative
should be followed exactly after making sure that your vet is aware that
they will be used for an airplane trip. Take your pet to the airport yourself
and make sure someone will be there to pick it up as soon as it is off
the airplane. Sitting around in a hot airport can be just as bad as flying
for a pet’s health. If you suspect your pet is ill, don’t send it on the
trip. If the weather is hot schedule trips at the cooler times of the day.
Sometimes it will be necessary just to accept that shipping a pet won’t
be possible for a few days or even a few weeks due to hot or cold weather.
Most pets do fine when they fly but you can help their chances by paying
attention to these basic rules.
New Format for the VetInfo Digest
Sometime in the next two or three months we are going to have to go
to a new format for the VetInfo Digest. We appreciate all of our early
subscribers who get the mailed version accepting our photocopied format
without one complaint. We are mailing over fifty subscriptions now and
photocopying and collating the pages is becoming time consuming. We are
negotiating with a printing firm and hope to go to a more traditional newsletter
that is professionally printed soon. We will probably have to stick to
an eight page format. Please let us know if you have suggestions for the
new format now or comments after we make the change.
We are trying to work out a way to have an easy to access subscription-only
site that we will develop while we maintain the current open access site.
We will try to develop an interesting and useful subscriber site that enhances
the value of the newsletter and the VetInfo web site.
Christmas tree and Hera
Pets almost always make Christmas more interesting. Sometimes they make
it more difficult, too. Our Christmas tree is usually fastened to the wall
with nylon fishing line because we have learned over the years that our
cats will climb it eventually. Our ornaments are all reasonable sturdy
because the rottweiler has a habit of running into the tree as she chases
the other pets around the house. We don’t put gifts that contain food under
the tree. We don’t use tinsel because I operate on cats that swallow it
occasionally. For the most part, our house is well prepared for Christmas
with pets. But sometimes the pets still find a way to make us remember
them at Christmas time.
For a while we had a Moluccan cockatoo at our house whose name was Hera.
Despite being named after a female god, Hera was a male. His eye rings
were visible and he really should have been a girl according to the books
we had read. We have a history of naming our parrots prior to finding out
what sex they are, so we also have a male Amazon parrot named Suzy. Not
knowing enough to use unisex names was only the beginning of our ignorance
about owing parrots.
Moluccan cockatoos are big parrots. They are very social and want to
be with companions at all times. They are also very adept at destroying
anything wooden and most things that aren’t wood, when they set their mind
to it. At least that has been our experience with them. They are also pretty
intelligent and capable of defeating reasonable measures for cage security.
Hera could open almost any type of snap, buckle or device used to keep
his cage door shut. Most of the time we just let him roam around with us
when we were home but you can’t take a parrot with you everywhere so there
were times when it was necessary to secure him in his cage. Despite a genuine
effort to watch Hera, our house had lots of evidence that we had a parrot.
There was a hole in the plaster wall that Hera created one day. He had
eaten the molding off the doorways in a couple of spots in the house and
there were always wood chips around his cage from chewing up the wood we
let him have to satisfy his chewing urges. We were on our second or third
attempt to find a method of keeping him in his cage when we left to go
Christmas shopping, hoping that this time we had figured out a way to keep
him in.
After being gone for several hours we came home and noticed that the
Christmas tree lights were on. No one remembered leaving them on but we
weren’t too concerned because we were home and there hadn’t been a fire.
A sudden flash through the window did cause us to drop everything and run
into the house, though. We couldn’t figure out what the popping sound was
as we rounded the corner to the living room. It didn’t take long to figure
it out, though.
Hera was sitting in the top branches of the Christmas tree, with the
string of Christmas lights in one foot and the other foot grasping one
of three remaining branches on the tree. He had apparently walked over
to the Christmas tree after foiling our latest attempt to keep him in and
methodically climbed up it one branch at a time while stopping long enough
at each branch to bite off the branch immediately below the one he was
standing on. Either he had turned the switch on at the extension cord or
we had left it on. Somewhere near the top of the tree he had decided to
grab the Christmas tree lights and had bitten the bulbs, breaking them
one at a time. We saw him bite two as we ran towards him and he really
looked happy with the sound they made. These were the old style big tree
lights, not the little ones used more frequently now. He was passing the
connecting electric cord through his feet as fast as he could, biting off
each bulb as it went by.
Why Hera didn’t kill himself chewing on the bulbs is more than I can
figure out. Good luck, I guess. Why it hadn’t occurred to us to buy a Master
lock for his cage door before this episode is also hard to figure out.
Buying a new Christmas tree a couple of days before Christmas was expensive.
Our mantel looked nice with all the evergreen boughs, though. We were thinking
of changing Hera’s name to Houdini after a couple of weeks, though. We
found that it took two padlocks to keep him in! And we don’t use a switched
extension cord for Christmas tree lights anymore. We just unplug the cord
in an effort to prevent future electrocutions.
New Cancer Vocabulary Terms
There are several terms related to cancer that are becoming important
to know. Cancer therapy is evolving rapidly and a great deal of the new
research revolves around several areas that you may not have heard of.
Apoptosis is the process of "programmed cell death". For some
reason the word is pronounced "apotosis", probably because it is a Greek
word that has something to do with falling leaves. Cells in the body could
theoretically live very long life spans. Nerve cells and some white blood
cells have the potential to live the entire life span of the pet. But many
other cells live much shorter life spans. Knowing how these cells are "programmed"
to die may help to understand why cancer cells don’t die or even help in
the development of a treatment that will trick them into dying when they
ordinarily wouldn’t. Conversely, an increased rate of cellular death sometimes
occurs in tumors that are spreading, apparently a group attempt at suicide
to stop the tumor spread. High levels of cells exhibiting signs of apoptosis
can be an indication that a tumor is dangerous. Even though researchers
have known for a long time that there was a process like apoptosis going
on in cells it seems to be only recently that researchers realized that
increased cell production was only part of the cause of cancers -- that
decreased cell death was also a factor in some tumors. As is the case in
many diseases and disorders it is unlikely that one factor alone leads
to tumor formation but knowing how and why cells die under normal circumstances
really might help to understand why the don’t die in tumors.
Angiogenesis is the name of the process that occurs when a tissue,
normal or cancerous, attracts a new blood supply. Cells have to have a
source of blood within 10 to 15 microns ( about 0.1 to 0.15mm) in order
to live. So a tumor can’t grow larger than this size unless it attracts
a blood supply. There are some cancer researchers who believe that cancers
may be pretty common -- perhaps present in most pets -- but that these
tumors never grow because they can’t cause angiogenesis. Without being
able to attract a blood supply they just exist at a small size until they
die or the pet dies before they can grow. Shark cartilage is perhaps the
most high profile inhibitor of angiogenesis. Thalidomide is another powerful
inhibitor of angiogenesis. It may resurface as an important cancer therapy
despite its previous problems due to this. Researchers are studying other
natural inhibitors of angiogenesis. It is important to remember that inhibiting
blood vessel infiltration doesn’t kill tumors, it just stops them from
spreading. This is very important but it does mean that inhibitors of angiogenesis
will probably have to be given lifelong to patients suspected of having
a primary tumor.
Oncogenes are aberrant genes that may be produced from normal
genetic material involved in cellular growth. When the normal genetic sequences
are altered in some way they may cause increased cellular reproduction
or other effects that help to produce cancer. There may be a link between
oncogene formation and the problem with vaccine induced sarcomas in cats.
Tumor suppressor genes are normal genes that are present in the
cell DNA and that inhibit the formation of tumors or activate apoptosis
when tumor formation begins to occur. Activating these genes or preventing
their inactivation in some cases, would help to control tumor formation.
Control of one or more of the above factors will aid in the control
of cancer formation and cancer growth. These are important areas of research.
Some successes with control of these factors have already occurred in mice
and other laboratory animals but it will probably be some time before there
is widespread success with use of these compounds in pets or humans. Hopefully
we can look forward to the day when that will occur, though.
Thanks for supporting us!
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This page was last edited 06/21/04
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