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Vet on call: Beware, not all laboratory results are free of errors

Friday March 20 2020
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Wairimu Kanyiri with her dairy cows in Kirangi Village, Turi. A good veterinary doctor should always express their sentiments in questionable laboratory test results and engage the facility to try and understand the source of the error. PHOTO | JOHN NJOROGE | NATION MEDIA GROUP

By DR JOSEPH MUGACHIA

Laboratory testing in both veterinary and human medical practice is a crucial ingredient of disease diagnosis. It is nowadays considered the gold standard for best practice in health services.

Incidentally, just like in other areas of medical practice, the analysis reports sometimes may be inaccurate and lead to improper treatment or management of a disease.

In veterinary medicine, such results, if not detected early, may result in improper and expensive treatment. The disease may escalate, cause death to the animal and unnecessary loss to the farmer.

You may recall last month (Seeds of Gold, February 19), I shared a black quarter case in a cow where I had submitted samples for laboratory analysis. I have since received the lab report.

Unfortunately, the test results were completely out of sync with my post-mortem (PM) findings. Such results cannot be considered for confirming the diagnosis of the problem.

In veterinary practice, PM observation, testing for disease confirmation in the lab is the gold standard for diagnosis of diseases in the field.

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Most causes of death leave tell-tale changes in the body that inform the doctor on the disease and cause of death.

Laboratory testing, on the other hand, seeks to identify the agent or agents that caused the disease and death.

Post-mortem findings are more likely to be erroneous due to the doctor’s inadequate knowledge and experience than laboratory results.

This is because laboratory tests follow laid down protocols that use various standardised materials and equipment. PM examination is based on visual observations by the doctor. However, experienced doctors become PM “diagnostic machines” and give highly accurate diagnoses in most cases.

A good veterinary doctor should always express their sentiments in questionable laboratory test results and engage the facility to try and understand the source of the error.

If the various professionals involved in the diagnosis and laboratory testing transparently engage, they will always confirm the source of the error.

I found myself contesting the results I received from the laboratory on the black quarter case. My two intern doctors, Eddy and Joyce, were the first to notice the anomalies when they received the results on email.

GAS ACCUMULATION

Joyce was on duty regarding laboratory issues that day. She discussed with Eddy and they informed me the results did not look right.

The laboratory had suggested Daisy died of a bacterial infection. They said they isolated Corynebacteria species that were resistant to most drugs used in animal treatment.

I had no problem with the resistance findings as the bacteria species is notorious for drug resistance. My problem was with the bacteria family apparently isolated from my samples.

The laboratory test report was completely inconsistent with the PM findings. By all counts, there was no chance in the universe that the bacteria could cause sudden death with blackening of tissues and gas accumulation under the skin.

You see, most disease-causing microorganisms, including viruses, have unique footprints that they exhibit during infection and also by the time the animal dies.

That is why an animal health service provider in most cases diagnoses a disease and treats your animal without taking samples to the laboratory. Many farmers are witnesses that most of their animals recover after such treatment.

My PM findings had shown Daisy had died of black quarter whose signs of sickness and death I explained fully in the article.

Corynebacteria species commonly cause cattle diseases but their main footprint is production of pus in boils or mastitis.

The only time members of this bacterial group could cause sudden death is if the germs formed a large abscess on a major blood vessel and caused it to burst.

This would cause the animal to quickly bleed to death. I have only seen such abscesses in the lungs of cattle on three occasions in the entire course of my practice.

Daisy had no abscess in the body but had evident areas of severe tissue blackening in the heavy muscles of the neck and shoulders.

The cow also had heavy accumulation of a foul-smelling gas under the skin. It is only some members of the Clostridium species of bacteria that are known to have these signature effects.

INACCURATE TEST RESULTS

Therefore, the difference in the signs of diseases caused by the two bacterial species and the PM findings leave no room for confusion.

I called the doctor who signed off the report in the lab and expressed my disagreement with the results. I sent her the full post-mortem report, including photographic evidence. She was in agreement that something went wrong and would investigate.

There are many reasons why a laboratory can return inaccurate test results. Most of the causes are human errors because majority of laboratory tests are automated.

The most common errors are those related to sample recording, often called paper work mix-ups. Once a sample is submitted to the laboratory, it is given a lab number and comprehensive recording to fit with the testing and reporting protocol. Erroneous recording may invalidate the whole testing process and results.

There are also procedural mistakes where the sample may get contaminated with other microorganisms because of inappropriate handling. Faulty equipment calibration or choice of the wrong test may also cause fatal errors and unacceptable results.

Sometimes the circumstances of the animal at the time of sample collection may also affect the test results. For instance, a milk sample taken from an animal under treatment may give incoherent test results.

Such milk may show mastitis to be caused by fungi while in reality, the fungi would have grown because of severe suppression of bacteria by antibiotics used for treatment.

If the submitting doctor provides insufficient information to the laboratory such as incomplete set of clinical signs observed in sick animals or post-mortem findings, the laboratory could make a choice of an inappropriate test and return erroneous results.

Finally, there are test results that could be false, negative or positive. These are mainly tests for the immune reaction of the animal body.

They are called immunological tests. Vaccinated animals may show false positive results while those with a weak immune system may show false negative results.

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