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Diagnostic testing-pick from the menu

horse menuAn unfortunate legacy of COVID-19 is the critical importance that better diagnostics tools could have played to mitigate the virus’ impact on human health and the world’s economy. And the lost lives.  As widely known in the industry, lab services account for less than 3% of total U.S. healthcare spending today, even though their test results impact a majority of all clinical decisions regarding patient care. Just as importantly, diagnostic testing saves horses lives.

The following case scenarios illustrate the folly of skipping diagnostic testing

A patients gums are very pale and anemia is a likely diagnosis.  In this case, the course of action is not directed with diagnostic point of care (POC) tests to provide actionable information, treatment commences with an iron supplement.  The intent is to “observe a treatment response”. You can take your pick of species in this example, be it goat, horse, or human.

If you picked a goat the most likely cause of anemia is parasitic and no amount of iron supplement will save the patient. The correct treatment is an effective anti-parasitic agent.  The anti-parasitic drug must be selected based on the parasite target--be it strongyle or coccidia.  An incorrect guess as to the parasite is just as lethal as treating parasites with iron. Picking the diagnostics from the a la carte menu is the best option.

If you selected horse as the example, a cause of anemia might be blood loss that is due to a guttural pouch mycosis. An iron supplement could help with chronic anemia, but supplements won’t prevent the eventual acute onset of lethal exsanguination—these horses often die because they hemorrhage from the nose.  Instituted early, surgery and medical treatment with various antifungal preparations can be effective.

Chronic anemia can be due to an inability of the bone marrow to produce red cells and differentiated from anemia due to blood loss.  Toxins, metabolic diseases-such as renal disease, and cancer can result in a lack of red cell production in humans and animals.

Diagnostic tests are selected and yield enhanced directed information, ultimately improving patient care and outcomes. Diagnostic tests save money.

What drove some people to rely on treatment response in dealing with equine sarcocystosis, a cause of equine protozoal myeloencephalitis (EPM) instead of pursuing diagnostic testing?  Perhaps it was confusing early messaging from leading experts in the field. The Western Blot was unable to distinguish between infection and disease. The Western Blot test failed to distinguish between species such as neurona, fayeri, and falcatula.  Experts failed to get the message out that antibodies vary in response to exposure, infection, and central nervous system disease.  An important lost message was that different tests measure different things.  It wasn’t the testing that failed, it was the messaging on what information the tests could reveal that missed the mark.

It took many years before three serotypes of Sarcocystis neurona were recognized. Once the serotypes were discernable, it was no longer necessary to use non-specific detection of apicomplexans that required reducing data to a probability.  And then there are the confusing experiments that absolved S. falcatula of infecting horses.  Failing to recognize that S. neurona, serotype SAG 6, is antigenically (highly) similar to S. falcatula made these infections indistinguishable with the available testing. And then there is the question of relapses.  Ineffective treatment led to the myth that most horses  with EPM will relapse. However, relapses are often a manifestation of another disease.  A disease that is a bystander to S. neurona…and not treatable with anti-protozoal agents.

The effects of an infection with Sarcocystis are innate immune responses that result in a peripheral neuropathy.  There are other causes of peripheral neuropathies.  The bystander mechanism, inflammation, results in non-demyelinating or demyelinating disease.  The pathophysiology of polyneuritis is a spectrum, from initiation to end-stage disease. Diagnostic tests can indicate the difference between non-demyelinating and demyelinating disease and direct appropriate treatments. With careful interpretation it is possible to stage the disease and that can help with clinical decisions.

The diagnostic menu for equine disease is constantly being developed and refined.  Each test gives a clue to the disease process and most importantly, diagnostics help predict the effect of a drug on the disease process.  A diagnostic test is used in conjunction with patient history, clinical signs, and clinician experience.  A diagnostic test can save money, time, and often lives. Once familiar with testing options, (https://pathogenes.com/w/epm-testing/),  rational treatments can be planned. If you need help reading the menu, give us a call.