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…