Vet Talk

Eliminating the Impossible: Diagnostic Tests

Medical cases are like mystery stories

May 14, 2013 (published)

“When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.” – Sherlock Holmes, “The Adventure of the Blanched Soldier,” Sir Arthur Conan Doyle

To a mystery fan, there is nothing better than following a trail of clues and slowly eliminating suspects, knocking them off one by one. I spent my youth honing detective skills by helping Hercule Poirot gather the members of the house party in the library over port, tromping through the swamps of Dartmoor with Watson and Holmes, and lingering over manuscripts with Lord Peter Whimsey. In veterinary school, the thing that helped me cling to the shards of sanity was the realization that medical cases were mystery stories.

All of the elements were there:

  • The victim – played by the patient
  • The suspects – potential causes of the disease
  • The clues – history, examination results, and diagnostic tests
  • The arrest and wrap up – the treatment plan

All that was missing was a deerstalker cap and meerschaum pipe.

I’ve spoken with other veterinarians who feel the same way about our amateur detective status. In fact, it’s a bit surprising that more of us aren’t walking around with monocles or oversized magnifying glasses, saying “Hmmm…verrrry interesting.”

However, I’ve found that the image of veterinary medicine held in the animal owner’s subconscious tends to involve more of a magic wand/crystal ball motif. I wish! It would be really cool to go all Dumbledore and wave a wand, and then pronounce a diagnosis that can be cured by finding all of the dog’s horcruxes plus a magic lamp.

For the sake of realism, however, let’s look at the diagnostic process, some of the more common tests, and maybe you too can be converted to the fun of the mystery.

Got your cap? Monocle? Mustache? Ok, the game is afoot! (or apaw or ahoof).

Our scene begins in a country mansion – or a busy veterinary clinic.

Mrs. Jones calls. She has found Fluffy surrounded by a perfect spiral of vomit. She swears that Fluffy was “fine that morning.”

Immediately, Mrs. Jones summons the local constabulary. Alternatively, she wipes up the kitchen floor, carefully preserving the contents of one bilious puddle in a Ziploc baggie, and brings Fluffy to the clinic.

The investigation begins:

Fluffy is a 5-month-old, unvaccinated, intact female Hell Hound. Unlike many Hell Hounds, she is of the rare single-headed variety, and suspiciously resembles a Rottweiler.

Clues 1-4: age, vaccination (or lack thereof), reproductive status, breed.

Upon interrogating the witness – I mean interviewing Mrs. Jones – the veterinarian learns that Fluffy takes daily walks to the dog park, is extremely obliging about cleaning the kitchen trash can each evening, eats “whatever we had for dinner; she’s a member of the family, after all,” was given three adult ibuprofen because she looked a little stiff after being hit “just a little bit” by a passing car, has never been dewormed, and that several of the family’s socks and Fluffy’s Easter bunny ears are missing. Also, there is an old family legend suggesting that a curse has been placed on the first Hell Hound born in every generation until the statue of a bird from Malta can be found.

Clues 5-12: dog park, kitchen trash, diet, ibuprofen, hit by car, no deworming, missing socks and bunny ears.

Clue 13: Family curse.

Forensic evaluation (examination) of the victim (patient) reveals a mildly lethargic, well-grown Hell Hound puppy. Her temperature is slightly elevated, heart and respiratory rate are normal, gums are a bit dry, heart and lungs sound good, abdomen is obviously tender, and Fluffy’s eyes glow ever so slightly.

At this point, the detective begins to generate a list of suspects with means, motive and opportunity. In medicine, we call this a list of rule-outs. Eliminating the impossible and all…

Just as the detective doesn’t have one method for evaluating fingerprints, footprints, the mysterious liquid in the vial, and the return of the squire and his manservant from a colony of warrior penguins in Antarctica, the veterinarian can’t assess each of the possibilities with one test.

In this case, our intrepid detective first heads in the direction beloved of all veterinarians: poop. She suggests testing Fluffy’s stool to look for parasite larvae and also to rule out a nasty critter called parvovirus.

Fluffy does have a small number of roundworms, but not enough to account for her current symptoms. However, starting a deworming program is discussed. The parvo test is negative even though Fluffy’s adorable Hell Hound skin has never been so much as kissed by a vaccine-wielding needle.

Since parvovirus alibied out (eliminating the impossible) and parasites have dropped further down the suspect list, the veterinarian recommends a test almost as classic and mythical as fingerprinting – blood-work.

To be fair, “blood-work,” “profile,” or “panel” usually indicate a series of tests wrapped up into one. Just like fingerprints don’t necessarily tell the detective who the murderer was, few blood tests actually produce gold-starred results saying “Your patient has disease X.” Fingerprints may (if the detective is lucky) reveal who was at the scene of the crime. Most of the factors analyzed in standard blood profiles show indications of damage to certain organs or imbalances in electrolytes and other nutritionally derived factors, or indications that the immune system may be responding to a virus, bacteria, or some other invader.

In this case, Fluffy’s blood work shows an elevated red blood cell count (referred to among savvy detectives/veterinarians as hemoconcentration, which is the opposite of anemia), and elevated protein and sodium levels. After a puff or two of the meerschaum pipe, the detective surmises that Fluffy is dehydrated. Her pancreas, liver, and kidneys appear fairly happy, bumping the kitchen trash can and ibuprofen down the list. The trash can, ibuprofen, dog park, and parasites are chatting over coffee in the break room and congratulating themselves on having got off.

The car, the bunny ears, and the curse are looking better and better.

Curse detection generally requires referral to a specialist, but there are diagnostic tests that are pretty good at bringing to light conditions such as trauma and bunny ear/sock impaction.

Of these, radiography (x-ray) often gives the most bang for the buck. On an x-ray, things that are the most dense (bones, Hellhound heads) look white; softer tissues like intestines, liver, stomach, and heart look grey-ish; and air (in lungs, outside lungs, in intestines) is black. Foreign objects, such as bunny ears and socks, might show up in changes in the patterns of air, fluid, and tissue in the intestines, or may require a contrast medium (a liquid that shows up white on radiograph) to outline them.

Fluffy’s radiographs showed several cracked ribs and changes in the intestine. A contrast study showed a spot where contrast was pooling but not continuing through the intestine.

At this point, the veterinarian has narrowed the suspect list to the car and the bunny ears. She recommends one more test – surgery.

Most folks tend to think of surgery as more of an answer than a question. But just like sometimes the detective has no choice but to round up the suspects and force a confession to discover the murderer, some patients have to be literally opened up to the light in order to reveal the cause of the illness.

In surgery, the veterinarian removes a stray sock from the intestine. It turns out that the oldest child tried to put the bunny ears on his younger sister’s head and she threw them over the fence.

Oh, and the curse? The butler did it.

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