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…

13 Weeks of Vet School… (Day 117)

Required Reading from first semester of vet school

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Something that has been my mantra of vet school so far is it is the quantity of information that I have needed to learn rather than the complexity (jinxed myself for next semester now!). Over the past semester my time has been very limited as its been stressful trying to balance fundraising for next semester with actually studying, revising and passing exams. So without further ado, lets put it all into context…

Required Reading from first semester of vet school
First semester of vet school required memorising!

Obviously this is a considerable amount over the 13 weeks, with a minimum of 30 hours a week in lectures and practicals I decided to try and break down my average week over the first semester. Depending on exams the amout of extra study per week did vary considerably.

There are 168 hours in a week
Minus 56 (8 hours a night) hours sleep = 112
Minus 30 hours scheduled practicals/lectures = 82
Minus 11 hours between lectures writting up notes = 71
Minus 3 hours a day for travelling, shopping, food + showering = 50
Minus 6 hours anatomy self study, 3 hours histology self study = 41
Minus avg 3 hours reading, revision & further study per subject (24 hours week) = 17
*** Minus whatever left doing diary, writting emails, and looking for funding = 0

*** – Depending on the urgency for grant applications or letter writting I did sacrifice study time to fundraising.

Anyways, onto what I am supposed to know now…

Was definately one of my most demanding subjects with a credit test every single week. During the 13 weeks the entire skeleton, all the muscles, joints and ligaments for the 7 major animals (Cow, Horse, Sheep, Goat, Pig, Dog, Cat) were covered. Whilst having similar bones and muscles there are differences in the shapes, size, attachment points and ligaments between species which all need to be known.

There were 3 credit tests this semester which involved being able to identify an organ by looking at its tissue and cell structure under the microscope in addition to knowing the function and normal structure. In the 13 weeks I covered epithelium, connective tissue, supporting tissue, blood, muscle tissue, nervous tissue, cardiovascular tissue, lympthatic system, endocrine system and the nervous system (whooo try reading that list out loud!).

One of the most practical subjects with plenty of laboratory tests covered. This looked at the different body systems, their normal function and diagnostic tests associated with them. It included blood, nervous system, cardiovascular system,  respiratory system, urinary system, immune system, digestive system, physiology of birds, metabolism. The practical sessions looked at different laboratory tests for each body system with around 25 different tests just for looking at blood!

One of my favourite subjects of the week this was a refresher to and built upon Microbiology in my previous degree. It included bacteria classification, identification, morphology, structure, reproduction, growth, distribution, genetics, plasmids, mutations, and horizontal transfer of genetic information. The practical sessions included a ton of different culture mediums, special staining methods, testing metabolic activity, molecular techniques such as PCR, and bacterial resistance.

The most intense subject nearly drowning me in infomation, its a single book of 122 pages, however the depth of the lectures was extensive and I used two textbooks to help me out here. The 6 year program has this subject over 13 weeks, where as we had everything crammed into the space of just 5 weeks so the practical time also went to lecture which I didn’t really like as I am an active learner. We covered antigens & antibodies, innate immunity, adaptive immunity, immune response, immune mediators, complement system, pathogenic mechanisms, serology, immunofluorescence, elisa, phagocytosis, lymphocytes, bacterial diagnosis, and hypersensitivity.

Ok I have a love/hate relationship with genetics; the practicals are usually very interesting and highly practical (I got to take bone marrow from a cow!) yet the lectures are very indepth and intense. Topics covered included genetic material, cell divisions, genetic analysis, pedigree analysis, chromosomes, sex and abnormalities, blood groups, inheritance, karyotyping, chromosomal abnormalities, genetic protection in breeding, genotype frequencies, mutagens and cancerogenes, gene mapping and GMO. Genetics involves a lot of maths which is a good thing, however the amount of information is staggering with 3 textbooks being given as additional reading to the 130 pages in the course text.

Milk Hygiene
Another topic that I did enjoy was milk hygiene, basically if you think about everything you know about milk and then every product ever made from milk this is what it covered. The most memorable moment was when we accidently set butter on fire in the lab! Now this semester we covered milking procedure & equipment, legal requirements, butter, cheese (cow/sheep/goat), cream, yougurt, icecream, diseases of milk, microbiology of milk, components of milk, sheep milk, goat milk, pastuerisation, sterilisation. And in the practical sessions we covered all the different tests that were used in quality control of milk and milk products and the tests used to ensure milk is safe for human consumption.

Slovak Language & Latin
Both of these languages are very different to english (they use things like genders for words etc) and language has never been a particulary strong point for me. With Latin I now know enough to describe most medical problems, and with Slovak can have basic conversations, shop and order food. I do still prefer English though!!!

Now with 13 weeks gone, I have passed some exams however still have the big 3 (Genetics, Anatomy, and Milk Hygiene) to go. In addition I am also working furiously to try and raise the additional £1700 for tuition I need to continue studying next semester!

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Hypersensitivity (allergic reactions) and washing cats… (Day 92)

Drying a cat

Today was the last Immunology lecture and was looking at hypersensitivity reactions in animals. Hypersensitivity is when the immune system exagerates the response to allegens (which is the name for antigens involved in hypersensitivity reactions) and is the cause of most allergic responses. There are four different types of hypersensitivity reactions…

  • Type I – Reaction mediated by IgE – atopy
  • Type II – Reaction mediated by IgG and IgM -cytotoxic
  • Type III – Reaction mediated by immune complexes
  • Type IV – Reaction mediated by cells – delayed type hypersensitivity DTH

Now type 1 hypersensitivity is usually caused by genetic or environmental factors, with the levels of IgE (a immunoglobulin responsible for the immune response) being higher than normal. The reactions are usually localised and form your general allergic reactions such as hayfever, asthma, conjunctivitis, food alergys and atopic dermatitis. This is usually tested for using intradermal tests where small amounts of the substance are placed under the skin and the results monitored or by using serum tests in a laboratory.

Type 2 hypersensitivity usually involved IgG and IgM and the complement pathways (the cell interactions for destroying cells). The IgG and IgM cells are produced that act against the bodies own cells, with the activated complement pathway which then destroys the cells. This often occurs with transfusion reactions or against red blood cells in new born animals such as foals which are born healthy and then sicken several hours after suckling for colostrum. This is tested for by a direct or indirect coombs test which works by testing the blood against the antibodies showing agglutination (cells sticking together) when it is positive.

Type 3 hypersensitivity involves soluble immune complexes, the complement system and neutrophils. These soluble immune complexes are deposited in tissues and organs which then activates the complement pathways causing inflammation and distruction of tissues. It is often responsible for pneumonitis, rheumatoid arthritis, rheumatic fever and associated conditions. There are ELISA tests available to test for this in addition to testing of the levels of the immune complexes or the presence of antibodies.

Type IV hypersensitivity (also called Delayed Type Hypersensitivity) involves Th1 memory lymphocytes, macrophages and cytokines. As it is cell mediated it has a prolonged onset (hence the “delayed type”). Generally this is contact allergy where as exposure to a substance for a second time causes a exageratted inflammatory response. The most well known of these is the response to TB, if the body has been previously exposed to TB, then when the skin test is taken an abnormally large response is recorded.

I am at the stage now where I can see the stuff I am learning being directly beneficial to me when I reach practice and start seeing animals which is pretty cool. Animals are fun when they are well, however sometimes they are not. This evening (well more like 10pm) I helped a friend wash her cat after he laid down in his own urine. Most cats would try to kill you if you washed them, however this guy is so tame that he barely objected, and most definately enjoyed being toweled dry…

Cat being washed = I'll get youAnd off course the cuteness here makes it all worthwhile…

Drying a cat