This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
The American Diabetes Association (ADA) recently lowered the cut off value for fasting glucose used in diagnosing diabetes mellitus from 140 mg/dL to 126 mg/dL. This reference interval change would be expected to produce which of the following alterations? 
Select and explain. 
A. Decrease the test's sensitivity, B. Increase the test's false negative rate, C. Increase the test's negative predictive value, D. Increase the test's positive predictive value
C: Increase the test's negative predictive value
Answer: C: Increase the test's negative predictive value 
Explanation: The negative predictive value of a test (PV-) refers to the percent chance that a normal test result is a true negative (TN; a healthy person with a normal test result) rather than a false negative (FN; a diseased person with a normal test result). It is expressed by the following formula: PV- = TN/(TN + FN) Similarly, the positive predictive value of a test (PV+) reflects the probability that an abnormal test result represents a true positive (TP) rather than a FP (a TP is an abnormal test result in an individual with disease, while a FP is an abnormal test result in a healthy person). PV+ is calculated using the following formula :PV+ = TP/(TP + FP)