A PEN-FAST score less than 3 is associated with which predictive value?

• A. Negative predictive value
• B. Positive predictive value
• C. Overall accuracy
• D. Sensitivity

Answer: (A)

A low PEN-FAST score is used to rule out penicillin allergy in a patient. The most relevant measure for a negative classification is the negative predictive value—the probability that someone who scores below the threshold truly does not have the allergy. Because a score under 3 designates low risk, the chance that these individuals actually lack an allergy is high, so the NPV is high. In practical terms, many patients with a low score can safely proceed with penicillin without further allergy testing, reflecting a strong negative predictive value. Predictive values depend on how common penicillin allergy is in the population, so in settings with low allergy prevalence, the NPV is even higher. The other metrics describe different aspects: positive predictive value relates to how likely those with a high score are actually allergic, sensitivity concerns how well the test catches all true allergies, and overall accuracy mixes both false positives and false negatives without focusing on the reliability of a negative result.