CICM SAQ 2010.1 Q19
Questions
19.1. To evaluate a new biomarker as an early index of infected pancreatic necrosis, you perform the measurement in a consecutive series of 200 critically ill patients with pancreatitis. You find that 100 of these patients had subsequently proven necrosis. Of these, 60 had a positive biomarker result. Of the remaining 100 patients without necrosis, 35 had a positive biomarker result.
Using the above data, show how you would calculate
- a) Sensitivity
- b) Specificity
- c) Positive predictive value
- d) Negative predictive value
19.2. A randomized controlled clinical trial was performed to evaluate the effect of a new hormone called Rejuvenon on mortality in septic shock. 3400 patients with septic shock were studied (1700 placebo and 1700 in the Rejuvenon arms). The mortality rates in the placebo and the treatment arms were 30% and 25% respectively. Calculate:
- (a) The absolute risk reduction
- (b) The relative risk reduction
- (c) The number needed to treat
Answers
Answer and interpretation
19.1. Calculate sensitivity, specificity, positive predictive value and negative predictive value.
- Sensitivity = (TP/{TP+FN}) = 60/100
- Specificity = (TN/{TN+FP}) = 65/100
- Positive predictive value = (TP/{TP+FP}) = 60/95
- Negative predictive value= (TN({TN+FN}) = 65/105
19.1. Calculate ARR, RRR, and NNT.
- ARR = 5%
- RRR = 5/30*100 = 16.6%
- NNT =1/0.05 = 20
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CICM
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
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