Diagnosing Pancreatitis Before It’s Too Late
Pancreatitis is almost as frustrating for doctors to deal with as it is for dog owners. It’s one of those diagnoses that is incredibly difficult to make before it’s too late. The symptoms are vague, and the current tests are hard to perform, unreliable, or both. That’s why it’s so important that researchers continue to hunt for a simple and effective way to diagnose pancreatitis. It’s not an easy task.
Diagnostic tests are evaluated on two criteria – sensitivity and specificity. The sensitivity of a test measures how good it is at detecting dogs that have the condition it’s looking for. A diagnostic test for pancreatitis with a sensitivity of 85% would correctly identify 85 out of every 100 dogs with pancreatitis as having the disease. In contrast, the specificity of a test measures how well it identifies dogs who don’t have the condition of interest. A diagnostic test for pancreatitis with a specificity of 90% would correctly identify 90 out of every 100 healthy dogs as not having pancreatitis.
The thing is, the usefulness of a test depends on not just sensitivity and specificity but how common a condition is in the population where the test is being used. After all, in the vet’s office, you don’t know if any dog has pancreatitis or not – that’s what you’re trying to find out. However, if you know how common pancreatitis is, and the sensitivity and specificity of the test you’re using, you can determine its positive predictive value – the likelihood that any positive test you get is actually accurate. That’s important because you don’t want to treat a dog for pancreatitis if you don’t need to, but you do want to intervene if it will help. A positive predictive value of 85 tells you that 85 out of every 100 dogs who test positive are actually sick – a much more valuable statistic for the clinician than the sensitivity. In fact, it turns out that the positive predictive value is actually far more dependent on the specificity of the test than the sensitivity in most circumstances.
All of that explains why, with the help of support from the AKC Canine Health Foundation, researchers from the University of California, Davis recently set out to investigate the sensitivity and specificity of a new blood test for pancreatitis and compare it to several other blood tests that might be useful in detecting the disease. The developers of the test, known as the Spec cPL, had determined its sensitivity as 63.6%, but they hadn’t figured out how specific it was – which meant it was difficult to tell how accurate any positive results might be. One previous study had investigated the same question, but more data was clearly needed.
They got it. The scientists found that the Spec cPL was relatively sensitive and specific, depending on the specific cut off values used for the tests. There was a tradeoff, as there often is, found when they chose different cut off levels – increasing the sensitivity of the test came at the expense of specificity, and vice versa. However, Spec cPL clearly provided better diagnostic results than any of the other tests they tried, giving hope that it might one day ease the diagnosis of canine pancreatitis. Further research is still needed, particularly as the study contained few dogs with healthy pancreases, which could affect the calculated specificities. Still, this research moves us one step closer to a reliable blood test for canine pancreatitis – a safer, easier way to start treatment and improve the quality of dogs’ lives.
This work was funded by AKC Canine Health Foundation Grant 1227-A.
Trivedi, S., Marks, S., Kass, P., Luff, J., Keller, S., Johnson, E. and Murphy, B. (2011), Sensitivity and Specificity of Canine Pancreas-Specific Lipase (cPL) and Other Markers for Pancreatitis in 70 Dogs with and without Histopathologic Evidence of Pancreatitis. Journal of Veterinary Internal Medicine, 25: 1241–1247. doi: 10.1111/j.1939-1676.2011.00793.x
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