Why negative tests at the vet suck…

Babesia blood smear - typical two tear drops

Today’s Diary Entry is sponsored by Spikes World

I am not quite sure how I got to this subject today, however it is something that I thought I would share my thoughts on from the past couple of months. After all as vets we will use tests to work out what is wrong, yet just what are we looking for?

Now diagnostics has played a big part in my life over the past 50 or so days, I’ve seen many physical exams, listened to tons of hearts, and watched countless breathes. I’ve looked at hundreds of radiographs, seen quite a few ultrasounds, and looked at blood and parasite slides.

I believe there are two ways that tests can be used. You can either confirm or eliminate a diagnosis. Personally when I look at a radiograph I am hoping to see something wrong. If we can see something wrong then can attempt to fix it.

So we look at a radiograph, and we see nothing abnormal. Is this really good? Personally I am on the fence here, not seeing anything means that I still don’t know what is wrong. Then there is the other problem, not everything will show up on a radiograph, so sometimes we use special foods or liquids to increase the contrast so we can certain things more clearly. Because we’ve not seen anything on the normal radiograph, does that mean we need to do a contrast radiograph? Or does it mean there really is nothing there?

Same with looking a blood slide under a microscope. If I see something is there it means I know what should be treated… If I see nothing is it because there is nothing? Or just nothing in that drop of blood? Or because it will not show up on the stain I used? Or worse, did I miss the 1 single abnormal cell within the 1000 cells that were on the slide?

Or how about the skin scraping looking for parasites causing the patient to have itchy skin… If I didn’t find anything does it mean that it is not there? Or did I not scrape deep enough? Or scrape in the wrong place?

The worse is the patient where all the diagnostic tests are normal, but the patient’s clinical signs show that they are sick… We can do test after test and they all come back negative…

Sometimes I think diagnostic tests are a dangerous thing, if not used properly they can be a time consuming and very expensive stab in the dark. However what are we supposed to do when they are negative and we are forced into the elimination route of diagnosis?

Is it because the test didn’t work? Or because it really is a negative?

Diagnostics are improving, yet it really is down to the skill of the clinician that uses them that determines just how useful they are….

P.S. For anyone wondering about the picture today, it is babesia, it is the third blood slide that was made for this patient as the first two were negative…

Why the urine is so important (aka Urinalysis)… (Day 122)

Urine Sample for Urinalysis

Todays Diary Entry is sponsored by Pet Webinars

One of the cheapest, quickest and most basic of tests used within veterinary practice is that of urinalysis, where the urine is examined and used to help diagnose disease. This test can be used as an indicator of disease in the kidneys, with digestion and within the urinary tract itself.

The first step in urinalysis is actually collecting the urine to examine, now unlike humans animals tend to have a problem with peeing in a cup. Now for certain parts of urinalysis such as culture in a microbiology laboratory a sterile sample is essential, and this is normally collected using cystocentesis which is where a needle is inserted directly into the bladder. For general tests however less invasive methods are used to collect the urine as it flows (takes practice) or with cats using a non-absorbing litter in their tray for example. If this fails when an animal is proving difficult to collect a sample from a catheter can be used instead and is passed along the urinary tract and into the bladder. It is important that urine is examined as soon as possible because it deteriorates with artifacts such as the pH changing and the formation of crystals.

Urine Sample for Urinalysis
Urine Sample

Now once a sample is collected the first thing to do is to examine the gross sample for the appearance and smell of the urine. Previously in history doctors actually even tasted the urine however luckily that is not done anymore (on purpose anyways!)! The colour of the urine should be slightly transparent and yellow or amber, it should not be cloudy and the odour should be faintly that of ammonia.

Next the urine’s specific gravity is tested, this can either be done with a refractometer or with a hydrometer (which is something new I learnt here). This tells us the concentration (the liquid:solid ratio) of the urine which is how many water soluble molecules (such as toxins, waste products, metabolic waste) there are in the urine. The reference (normal) values for the specific gravity depend on the species of the animal being tested. Though not a complete list some of the diseases that this points to include dehydration, renal failure, excessive drinking, diabetes insipidus, glycosuria, decreased kidney blood flow and many more.

A dipstick test is then carried out to check many different parameters at once, depending on the test stick used this can include pH, glucose, leukocytes, blood (hemoglobin) content, Nitrates, Ketones, Bilirubin and Protein. Some sticks contain specific gravity however its not as reliable as using one of the previous test methods. Something worth remembering here is that once urine is applied the stick should kept horizontal to prevent contamination between the tests. In fact some places actually pipette a drop of urine onto each test square instead of dipping the stick! All of these parameters point to different diseases and body systems.

Finally the urine is examined under the microscope for cells, crystals, parasite eggs, and fat all of which should not be present in urine. Cells can indicate problems physically with the tract and bladder, whilst crystals can indicate further problems with bladder stones. Parasite eggs obviously indicate parasites, whilst fat is an indicator for digestion and renal diseases.

This is just one piece of the diagnosis puzzle that a vet works with, and because of the relatively low cost of urinalysis and ability to perform the test instantly in house is one of the most valuable.