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What Screening Lab Work Can Do For Your Pet

Screening Lab Work for Young, Healthy Pets

When it comes to the health and well-being of our beloved furry companions, we often want to go above and beyond to ensure their safety. However, there are instances where certain medical procedures or tests may not be necessary, especially for young and healthy animals. In this blog post, we aim to shed light on why a Complete Blood Count (CBC), Chemistry Profile, and Urinalysis may not be indicated as a prerequisite for anesthesia or as a baseline for such animals. By understanding the rationale behind these recommendations, we can make informed decisions about our pets’ healthcare.

About Screening Tests

Screening tests for conditions that can’t be treated doesn’t make much sense.  For example, unless you were planning on breeding your German Shepherd Dog, it doesn’t matter whether or not she carries the genes for degenerative myelopathy.  Your dog is either going to get degenerative myelopathy or it’s not, and there isn’t a darn thing you can do about it.  If you were going to breed the dog, then screening for DM makes sense, as you wouldn’t want to breed a dog that would pass that horrific disease on.  Well, if you were a good breeder, anyway.  But that’s not a disease that shows up in a typical lab panel; it’s a very specific DNA test.  Your dog could have 2 recessive (abnormal) DM genes and have perfectly normal screening lab work.  Also, until DM is in the very late stages, at which point it is NOT a young healthy pet, there are no contraindications for anesthesia.  

The assumption we make about young, healthy animals is that the people assessing their health are not idiots.  Now, I could tell you some stories about people being wildly wrong about what was wrong with their pet.  Like the lady who thought her puppy’s legs were broken because the puppy wasn’t walking.  The puppy was dead.  Which was a darned good reason for it to be not walking (or breathing for that matter).  

That said, MOST of the time, the pet owner is most familiar with their pet’s normal personality, and tips the veterinarian off when something is wrong.  Sometimes the veterinarian finds problems that the pet owner isn’t aware of, like tiny kidneys.  But we’re not talking about these animals.  We’re talking about perfectly normal pets who have been thoroughly examined by a competent veterinarian.

At-Risk Populations

 Screening lab work consists of tests run on an at-risk population where early detection and intervention improve the health of the individual or prevent illness entirely.  While human men can get breast cancer, the risks are quite low, which is why men don’t get routine mammograms.  Women get mammograms because when detected early, breast cancer can be cured.  When detected too late, it can cause massive suffering, huge costs, and death.  

In young healthy dogs and cats, there is very low probability that they are at risk for anything that will show up in screening lab work.  

Certain breeds may be at risk for certain diseases, but to test for these diseases usually requires a specialized test.  For example, Main Coons are at risk for hypertrophic cardiomyopathy, which can be tested by echocardiogram.  This is a procedure only a specialist in cardiology, diagnostic imaging, or internal medicine who has high-end ultrasound equipment can provide.  It’s not a simple blood test done by your general practitioner veterinarian.  

When Is Your Pet a Senior?

Using human recommendations, we like to start at least annual screening laboratory testing in pets when their human equivalent age is about 50 years old.  For cats, that’s about 10 years.  Small dogs reach seniority at about 8 years of age, giant breed dogs at about 6.  

How old is your dog in human years? Depends on the size of your dog. We recommend at least annual senior screening lab work in your dog when their human age is about 50 years old.
How old is your cat in human year? We recommend at least annual senior screening lab work in cats 12 years and older.

Sensitivity and Specificity

Sensitivity: Sensitivity refers to the ability of a screening test to correctly identify individuals who have the condition or disease being tested for. In other words, it measures the test’s ability to correctly detect true positive results. A highly sensitive test will have a low false negative rate, meaning it rarely misses individuals who have the condition. Sensitivity is particularly crucial when early detection or ruling out a condition is important. However, high sensitivity may also result in a higher number of false positive results, where the test indicates the presence of the condition even when it is not present.

Specificity: Specificity, on the other hand, measures a screening test’s ability to correctly identify individuals who do not have the condition or disease being tested for. It indicates the test’s ability to provide true negative results. A highly specific test will have a low false-positive rate, meaning it rarely indicates the presence of the condition in individuals who are actually healthy. Specificity is important when a high degree of confidence is required to avoid unnecessary follow-up tests or treatments. However, high specificity may result in a higher number of false-negative results, where the test fails to detect the condition in individuals who actually have it.

Tradeoff between sensitivity and specificity in lab tests

Trade-off between Sensitivity and Specificity: The trade-off between sensitivity and specificity arises from the inherent characteristics of the screening test. As sensitivity increases, the likelihood of false positives also tends to increase, thus reducing specificity. Conversely, as specificity increases, the likelihood of false negatives also tends to increase, reducing sensitivity. This trade-off is a result of the threshold or cutoff value used to determine whether a test result is considered positive or negative. Adjusting this threshold can shift the balance between sensitivity and specificity, but there will always be a trade-off between the two. There is no such thing as a perfect test.  

The choice of whether to prioritize sensitivity or specificity depends on the clinical context and the consequences of false-positive or false-negative results. In some situations, such as screening for life-threatening diseases, it may be more important to have high sensitivity to avoid missing potentially affected individuals.  The mammogram still causes some women unnecessary costs in biopsies and needless worry with an abnormal result, however we still get tested because those risks outweigh the risk of not detecting breast cancer early.  In other cases, where follow-up tests or interventions have significant risks or costs, high specificity may be preferred to minimize unnecessary procedures for healthy individuals.  This is why most older men don’t get the PSA test any more.  It was too sensitive, causing men to undergo expensive and painful treatments for a disease that would have never caused them any problems.  

With screening lab work, every single assay has its own sensitivity and specificity.  ALKP (alkaline phosphatase) is a value that is associated with liver disease, but it can be elevated due to severe bone disease, rapidly growing bones in young dogs, hyperadrenocorticism, severe GI disease, or with a completely benign liver condition in older dogs.  Very sensitive, but the specificity sucks.  OTOH, creatinine is used to measure kidney function.  If the creatinine is high in a well-hydrated animal, that pet has kidney disease.  Unfortunately, if the creatinine is high in a well-hydrated animal, 75% of kidney function is already lost.  Great specificity but the sensitivity is crap.  You’d like to intervene before the animal has half of one functioning kidney!

Biologic Variability and Reference Change Value

Biologic variability refers to the natural variations that can occur in physiological parameters within an individual’s body over time. It is important to understand and consider biologic variability when interpreting diagnostic test results, including laboratory values. One method used to assess significant changes in laboratory values over time is the reference change value (RCV).

The RCV is a statistical tool that helps determine whether a change in a laboratory result is clinically significant or simply within the expected range of biologic variability. It takes into account both the analytical variation (the inherent variability in the laboratory test itself) and the biologic variation (the natural fluctuations in the individual’s physiology) to calculate the minimum amount of change needed in a laboratory result to indicate a true change, rather than random variation.  

Think of analytic variation like this.  You weigh yourself first thing in the morning.  You look at the number, decide you hate it, get off the scale, wait a minute, and get back on again.  This time it gives you a slightly lower number.  Your weight didn’t change in a minute (unless you took off your clothes).  It’s just the scale has some variation.  The same thing happens with laboratory analyzers.  The number it spits out for each assay is somewhere within the range of the real number.  And that range varies depending on the assay you’re talking about.  Some lab results are pretty darned close to the truth and others can be wildly variable.  I’m sorry, but the bathroom scale is not that variable.   

Biologic variability plays a crucial role in determining the RCV. Since laboratory values can naturally fluctuate over time even in healthy individuals, it is essential to consider the extent of biologic variability when evaluating changes in test results. The RCV helps establish a threshold beyond which a change is considered significant and likely reflects an actual physiological change rather than normal biologic variability.

Biologic variation refers to the changes that happen just because stuff fluctuates.  When you get on the scale in the evening, after you’ve had 3 healthy meals and drank your gallon of water and exercised, it’s going to show a higher weight than it did that very morning.  Did you really gain 6 pounds in 16 hours?!  Well, technically probably yes, but it’s all water weight and just a normal fluctuation in the day.  Fluctuations can also be monthly (you ladies know what I’m talking about), your “winter weight” and so on.  These are fluctuations that occur as a result of living- your body changes throughout the day in response to the things we do to it.  Your glucose changes, your temperature changes, all sorts of things changes.  That’s biologic variation.  

By using the RCV, healthcare professionals can make more informed decisions regarding patient care. For example, if a laboratory value shows a change that exceeds the RCV, it suggests a real change in the individual’s physiology and may warrant further investigation or intervention. On the other hand, if the change is within the RCV, it is more likely to be a result of normal biologic variability and may not require immediate action.

It is important to note that the RCV is specific to each laboratory test and should be established based on rigorous statistical analysis and validated data. Different tests have different levels of biologic variability, and factors such as age, sex, and underlying medical conditions can also influence biologic variability.

Unfortunately for us vets, we don’t know the RCV for most of the lab tests we run.  So if your pet’s lab test is normal, maybe it is, maybe it isn’t.  If it’s abnormal, again, maybe, maybe not.  It might just be normal variation.  We have to run a lot of tests on your pet to figure out if the variation is normal for your pet- remember, these are individual variations.  So one lab test, especially in a young growing animal, isn’t really a “baseline.”  We’d have to run a lot of tests to find out what your pet’s true baseline is.  And we’d have to know more about the RCV for each test.  

Ethical Considerations

Ethically, veterinarians should recommend tests that may change what they do.  For example, if I am recommending screening lab work prior to anesthesia, there has to be a good chance that the results of the test will change my anesthesia plan.  In the case of young healthy dogs and cats, it is extremely rare that anything will show up with screening lab work that will affect my choices for medications, dosages, or monitoring.   If I know that the results aren’t going to change anything, then why should I run the test?

One argument veterinarians make is CYA.  It’s not a terrible argument.  For example, what if after a surgical procedure your pet started showing signs of kidney disease.  If I didn’t run pre-anesthetic lab work, you could argue that something in my anesthesia plan caused the kidney disease.  That is highly unlikely unless we totally screwed up the dose of non-steroidal anti-inflammatory drugs that we administered or sent home, which is extremely unlikely because I use a spreadsheet to calculate each dose rather than relying on anyone’s math skills.  But let’s say that happened- your pet was normal prior to their spay/neuter, and afterwards started showing signs of kidney disease.  I’d have a hard time proving that the pet didn’t already have kidney disease such that the normal dose of NSAIDs exacerbated the problem.  

I’ve been a vet since 2008 and a vet assistant from 1997-2008 and I’ve never seen that happen.  It could happen, it probably has happened to someone, but the likelihood of that happening doesn’t warrant testing all young healthy animals for kidney disease prior to surgery.  

Another argument made by veterinarians is that pre-anesthetic lab work is the standard of care.  It may be THEIR standard of care, but it is not THE standard of care.  How do I know?  Because nobody has ever defined THE standard of care!  It sounds absurd but I promise this is true.  Legally, THE standard of care is defined only when someone tests it in a court of law.  And then, it is only applicable to the case at hand.  Shockingly, THE standard of care is the minimum treatment that one should expect.  You should expect your veterinarian to perform a complete examination prior to anesthetizing your pet if it is safe to do so.  I have some patients who are not safe to examine when they are not anesthetized.  So even an exam is not THE standard of care in all situations!  

There is nothing wrong with having higher standards than the law.  Most veterinarians do have higher standards.  For example, there is no law that states you must give pain medications to a pet undergoing surgery; that is MY standard of care.  


Maximizing Resources

We each have limited budgets for pet health care.  Some budgets are much higher than others, but everyone has a limit on what they are willing or able to spend.  One of my jobs as a veterinarian is to use these limited dollars in the best way possible.  It doesn’t matter to me if you have millions of dollars or tens of dollars, screening lab tests in young healthy animals is not a good expenditure.  

Additionally, lab work takes time and effort for your pet’s health care team.  The samples are sent to a lab causing environmental impacts in shipping and running the tests.  There is the potential that obtaining the samples will cause emotional harm to your pet.  Obviously, we do everything we can to minimize stress in each pet, including sedation, but this adds costs and risks as well.  

Lab work in young healthy animals has minimal impact on their health.  I’d rather spend your money on appropriate vaccinations, parasite prevention, and optimal nutrition.  I’d rather spend our time understanding your pet’s lifestyle and personality so I can make the best recommendations.  I’d rather you save the money for illness or injury or training.  These things have a huge impact on your pet’s health.  Lab work is a much lower priority.  

What Does That Mean for Your Pet

As pets age, the likelihood of finding early onset disease in apparently healthy animals changes.  For example, a 16 year old cat that is very active, eats well, and seems normal to the pet parent may have hyperthyroidism.  Most pet owners don’t know their cat has a heart murmur, or that their 16 year old cat should be sleeping 23.5 hours per day.  When I run screening lab work on this pet, I’m not at all surprised if the T4 (thyroid hormone) is elevated.  In fact, if the T4 is normal, I may think it’s biologic variation.  

Screening lab work before anesthesia has not been shown to improve patient outcomes in human or veterinary medicine.  That’s because successful anesthesia is about maintaining parameters that are not measured in lab work- temperature, pulse, respiratory rate, oxygen saturation, end-tidal CO2, hydration, and blood pressure.  Most anesthesia drugs are not metabolized through the liver or kidneys, and do not cause damage to those organs.  I mentioned NSAIDs earlier.  A short course of NSAIDs in a healthy young dog or cat is highly unlikely to cause any problems with the liver or kidneys.  It’s unlikely that a healthy young dog or cat has pre-existing liver or kidney disease.  So pre-anesthetic lab work doesn’t change anything in the vast majority of patients.  

When Is lab work indicated?

Why blood work is important in older cats
Why blood work is important for older dogs

Older pets should have screening lab work at least yearly because they are at risk for certain diseases that will cause abnormalities in their CBC, chemistry panel, T4, and/or urinalysis.  That’s just because older pets are more likely to get cancer, thyroid disease, kidney disease, and other illnesses.  If we can catch a condition early, we have a much better chance for successful intervention than after the pet is sick from the disease.  

We should also do lab work on pets that have been diagnosed with a chronic disease such as kidney disease, Cushing’s disease, thyroid disease, or diabetes.  And some chronic medications require routine lab work, such as NSAIDs and phenobarbital.  

What About Diagnostic Lab Tests?

Diagnostic lab tests are different, even though they are the same tests.  In this case, we have a sick patient and we’re trying to find out what the problem is.  The results may give me a diagnosis, or may mean we have to run more tests.  For example, when we see abnormalities in the liver values, all we know is there is something wrong in the liver, but we don’t know what.  It could be anything from inflammation secondary to GI upset, Cushing’s disease, to cancer.  We don’t know without further testing such as ultrasound, more blood tests, or a liver biopsy.  


Bottom Line

I don’t recommend screening lab work in young healthy dogs and cats.  If you want to have it done anyway, it’s OK as long as you understand what the results mean.  Some people like the added peace of mind and don’t mind paying for it.  I’m good with that too, as long as all other aspects of pet care are optimized.  It’s just not necessary, so if you want to save your money for something else, please do.  You have my blessing.

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