You’ll often hear our vets talking about “running some bloods” or “doing a health screen”… but do you know what we’re actually looking for? Or what the results mean? If you want to know more about blood tests, this is the blog for you!
What tests can you run?
Well, we CAN run almost any test there is! However, the vast majority of blood tests we run in-house, in our own well-equipped laboratory. This means we can have the results in a matter of minutes, no more waiting for a courier to take the samples to the lab, and the results back in 48 hours… it’s almost immediate!
We have three sets of test equipment in our lab:
This machine measures the amounts of certain natural chemicals that are dissolved in the blood. By comparing those to the normal ranges (which are different from species to species), we can assess the function of a wide range of organ systems within the body.
For any one chemical, there are basically three things it can do – it can be normal (hooray!), higher than normal, or lower than normal. If the levels are elevated, that means either that whatever organ makes that chemical is leaking or working too hard; or that the organ that removes it isn’t working properly. If the levels are reduced, the opposite is true. So, most of the tests give us some information about two different organ systems (which is quite clever!).
This one measures the numbers of different types of cells in the blood. Not just red and white cells, but also platelets (that help the blood to clot) and all the different types of white blood cell. It can also tell us if the body is making new red blood cells unusually fast (e.g. in some types of anaemia), or not making enough (other types). The pattern of different white blood cells (neutrophils, lymphocytes, monocytes, eosinophils and basophils) can tell us a lot about how the immune system is working – is it fighting something, or is it depleted or unusually inactive.
This isn’t a machine sitting on the side, but a series of single-use test kits (they normally live in the fridge!). We use these to measure certain hard-to-detect substances in the blood, especially for signs of certain specific infections (e.g. Parvovirus, Feline AIDS, and Feline Leukaemia Virus).
OK, so what do the results mean?
Well, although there are lots of other tests we can run, some of the most important are:
Urea and Creatinine
OK, this is 2 tests, but we almost always run them side by side! These are good markers for kidney function – if they’re both high, it almost always means that the patient’s kidneys aren’t functioning as well as they could be. Occasionally we get a high creatinine with a normal urea – this can be normal in very heavily muscled dogs, as creatinine is made by the muscles; however, in most cases, elevations in these mean kidney issues.
Alanine transferase (ALT)
This is one of the “liver enzymes” that we routinely test. Normally, levels in the blood are very low, because the enzymes are carefully tucked away inside the liver cells. However, if the liver is damaged, many of the cells die and release their enzymes, so we see a spike in the levels in the blood.
Alkaline Phosphatase (ALKP)
This is the second liver enzyme. This one tends to rise in response to problems with the bile ducts, although we also get elevated levels in dogs with Cushing’s Disease, and animals on steroids or with bone problems.
This chemical is the yellow pigment that makes animals with liver disease turn jaundiced! However, even quite high levels aren’t always visible, so it’s really useful to measure it directly. Elevated bilirubin can occur in liver disease, but also some types of anaemia (as it’s released by damaged red blood cells), or problems in the bile ducts or pancreas (because the bile stops flowing).
This is a hormone made by the thyroid glands in the neck. One of the most common conditions seen in older, thin cats is an overactive thyroid – when we run an “old cat panel” we’ll often find that levels of T4 are sky-high, confirming the diagnosis!
Conversely, in dogs, underactive thyroids are more common, and can be detected in the same way, by an abnormally low T4 level. This also allows us to measure the effectiveness of treatment too.
Packed Cell Volume (PCV)
This is a measure of how many cells there are in the blood. Normally, red blood cells make up perhaps 30-45% of the blood volume (more in greyhounds, towards the lower end in most cats). An anaemic animal will have an unusually low count for their species, breed and age; whereas a dehydrated animal will be higher, because there’s less water in the bloodstream.
These cells are the immune system’s “shock troops” – they go into battle immediately when there’s an infection. However, they also die off in large numbers while fighting it (which, incidentally, is what pus mostly is – dead neutrophils that have sacrificed themselves to save the animal). So, in a suddenly very poorly patient, we might detect an infection by seeing a sudden drop in neutrophils (as they’re used up), and then a dramatic rise (as the body makes millions upon millions more to fight the infection).
While a blood test can’t always tell us everything that’s going on inside your pet, it can certainly point us in the right direction. It can also confirm which organs ARE working properly, and so help us avoid being misdirected! All in all, the “simple” blood test is one of the most powerful diagnostic tools available to us… and with rapid turnaround, it really benefits our patients!
If you’d like to know more, please feel free to pop in and have a chat with one of our staff!