Blood tests unmasked
There is an epidemic of macabre whodunit TV programmes and books at the moment and my job can also be a detective-type game, although with less of the red currant juice, dead bodies, glamour, hair-flicking blondes and racy cars.
But seriously, Dr Doolittle had it easy. Obvious, I know, but my patients can’t talk. They can wag their tails, purr, hiss, spit, growl and bark, but other than the odd cockatiel or parrot, I have never had a patient speak to me in English. So, at the pet hospital, we have to rely on lots of other things.
The one most important thing is your – the owner’s – observations and history. It amazes me every day when a patient comes in and the owner will say ‘‘she’s not quite right’’.
Where do I begin to look? But almost every time there will definitely be something wrong, which can often be a high temperature, for instance.
You know your best friend and companion, like any other member of the household. So what if an initial examination doesn’t find anything? That’s when it gets a bit tricky.
Or what if there could be a textbook full of possible causes – like all the possible causes for vomiting or all the hundreds of causes for diarrhoea?
We always discuss what we could do next and this could be several options, including trying a treatment, knowing that it will treat the most likely cause or the main symptom, or doing tests to find the cause or at least eliminate a few possibilities.
Usually a blood test is the first step. So what is a blood test? It seems to have a real prestige associated with it, as if a blood test will solve all the problems and find the cause. This isn’t always the case.
This is a huge subject, but here’s some of it. This is part one of two parts about blood. First, what is involved in a blood test?
Blood needs to be collected from an accessible vein. Interestingly, in the design of bodies, arteries are buried deep in tissues to protect them because if they are cut, the higher pressure in them will mean that they keep bleeding for longer and will lose a lot more blood than a cut vein. Veins are closer to the surface, which also allows them to play a part in heat control.
In my patients, the jugular vein in the neck is accessible and of a size that allows a sample to be collected. Leg veins in cats, for example, are often too small to collect from. The other consideration for us is keeping the patient still, so our patients often get a small sedative to relax them and make the whole experience a nice one, including stopping us getting shredded or eaten.
And what are all those different tubes the staff at Medlab collect off you? We use the same tubes. All the different tubes bar one just have different types of substances to stop the blood clotting. One tube hasn’t got anything in it, so the blood will clot.
Why? If you let blood clot, the clot will contain all the red cells, platelets and any other factors needed to form a clot. The remaining clear fluid above the clot is called serum. This serum is the main thing we use to test the state of various organs including the kidneys and liver. The tests are called biochemistry tests.
The blood in the other tubes won’t clot and is used to check the red and white cells.
White cells are principally involved in fighting infections. The red cell levels can indicate anaemia, for instance.
More about the actual tests next week.
So what is the main fallacy associated with blood testing? That it will indicate types of tumours. This is rarely the case, just like most tumours in people. However, tumours affecting the bone marrow where blood cells are made will show up and some tumours cause a couple of changes in levels of blood calcium and protein. Other than that, most tumours are not detectable with a blood test.
What about blood tests prior to an anaesthetic? This is a great idea and we often recommend it, especially with older patients whose kidneys and liver may not be functioning as well as they should be.
So, blood tests can confirm what we suspect, monitor how treatments are going, keep an eye on some diseases and rule out some things, but they also may be normal in an unwell patient.
Next week I’ll explain just a few of the tests we can do and a couple of great cases from this week that really benefited from those tests.