A research group evaluates a novel high-resolution ultrasound technique for diagnosing giant cell arteritis (GCA) in patients over 50 years of age presenting with new-onset headaches. A prospective study enrolls 1,000 such patients. Each patient undergoes the novel ultrasound followed by a temporal artery biopsy, which serves as the gold standard.
Biopsy results confirm the diagnosis of GCA in 150 patients. The novel ultrasound finding is present in 120 of these biopsy-confirmed cases. Among the patients with a negative biopsy, the ultrasound finding is present in 34 patients.
Based on these study results, what is the positive likelihood ratio () of this novel ultrasound finding for diagnosing giant cell arteritis?
Answer: 20
Answer
20
The positive likelihood ratio is calculated using the formula: LR+ = Sensitivity / (1 - Specificity). First, calculate the sensitivity: 120 True Positives / 150 Total Disease Positives = 0.80. Next, calculate the false positive rate (1 - Specificity): 34 False Positives / 850 Total Disease Negatives = 0.04. Finally, divide the sensitivity by the false positive rate: 0.80 / 0.04 = 20.
Step-by-Step Solution
Key Concept
The positive likelihood ratio (LR+) is calculated as Sensitivity divided by (1 - Specificity). It indicates how much more likely a positive test result is to occur in a patient with the disease compared to a patient without the disease.