North American Veterinary Licensing Examination (NAVLE) Practice Test

What is the predictive value positive (PVP) for a FeLV test with a prevalence of 5%?

1. 45%

2. 48%

3. 55%

4. 90%

The correct answer is: 48%

To calculate the predictive value positive (PVP) for a feline leukemia virus (FeLV) test, we need to consider the test's sensitivity, specificity, and the prevalence of the disease in the population being tested. PVP is influenced by the prevalence of the disease; as prevalence increases, positive predictive value generally increases. Conversely, with lower prevalence, the PVP may decrease even if the test is somewhat accurate. Given a 5% prevalence for FeLV, it indicates that out of 100 cats tested, approximately 5 would have the disease. The PVP helps estimate how many positive test results are true positives based on that prevalence. Assuming the sensitivity (true positive rate) and specificity (true negative rate) of the FeLV test are reasonably high, the positive predictive value can be effectively calculated with the formula: \[ \text{PVP} = \frac{\text{True Positives}}{\text{True Positives} + \text{False Positives}} \] With a low prevalence like 5%, this indicates that while the test may identify some true positives, the number of false positives could be proportionately higher compared to how many true positives are identified. This situation means the positive predictive value won't