Commentary: Considering Test Results in Context

KNOWLEDGE IS POWER. Actually, it's much more accurate to say "Factual knowledge in context is power."

Polymerase chain reaction (PCR) testing is an extremely sensitive test for biologic agents in horses. However, a positive PCR for Salmonella can indicate either the presence of live bacteria in the sample or dead bacteria with DNA still present. So, is the horse actively shedding live bacteria, or just DNA? The positive PCR test is a fact, but interpretation is everything.

Drug testing of human and animal samples for illegal substances has become extremely sensitive, in some instances detecting one part per billion of a substance. Is every positive drug test indicative of illegal drug use? The answer to this question is of obvious interest to high-caliber human athletes as well as horse owners.

Interpretation of ultra-sensitive test results has its own challenges. With the rapid advances in diagnostic testing technology in veterinary and human medicine, some people assume that test results are 100% sensitive (all positive samples are detected) and 100% specific (all negative samples are detected). However, no such test exists. In current biological diagnostic systems, some false positives and some false negatives are expected, with some procedures having 90+% sensitivity and specificity.

Even DNA testing is not 100% accurate, as the likelihood of confirming identity or paternity is dependent upon the number of DNA markers used in the test. The more markers tested, the greater the probability that two samples will match. However, probability is never 100%. Only an exclusion of identity or paternity can be made with 100% accuracy.

This doesn't mean that all diagnostic testing is worthless because of less than 100% sensitivity. Understanding of current technology--which is incredible compared to diagnostic capability of only 10 years ago and continually improving--makes diagnostic interpretation possible, and multiple tests can confirm results.

Weather forecasting is not an exact science, but horse owners have a significant interest in weather conditions. If property or animals are lost due to adverse weather events, people are affected both financially and emotionally. In addition, both fire and drought can directly affect nutrition, water supplies, and feed costs. Weather and drought predictions are based on history, facts, advanced computer modeling, and interpretation--not a crystal ball. Many people have complained about weather forecasts, but modern weather predictions for significant storms are impressive considering the difficulty of anticipating Mother Nature's tricks.

In today's world of high-speed communications, some misinformation or unverified information--even rumors--can run wild. The test of accuracy is in the reliability of the information source, understanding the overall situation, and monitoring updates for changes and corrections.

Whether it's accurate interpretation of diagnostic test results or predictions of adverse weather conditions, Factual information in context is power!

CONTACT: Dr. Roberta M. Dwyer, 859/257-4757;; Maxwell H. Gluck Equine Research Center University of Kentucky, Lexington, Kentucky.

This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd's, London, brokers, and their Kentucky agents. More articles from Equine Disease Quarterly...

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