Journal Club Summary

Methodology Score: 4/5                  
Usefulness Score: 4.5/5
Perry, Jeffrey J. et al. 
This prospective observational cohort study identified a cutoff as 2000 x 106/L RBC on the final CSF tube and no xanthochromia as a reasonable cutoff to reliably differentiate traumatic LP from aneurysmal SAH. The combination of these two findings resulted in a sensitivity of 100% (74.7 – 100), specificity 91.2% (88.6 – 93.3) and a LR+ of 11.4 (8.8 – 34.6). This diagnostic cutoff will help better inform clinicians when making the critical decision of whether or not to pursue further testing to diagnose SAH. 
By: Dr. Krishan Yadav
(Presented May 2015) 

Epi Lesson: Bayesian approach to pre-test and post-test probabilities

Thomas Bayes, an English mathematician, developed the idea of generating pre-test probabilities before applying a given test and then adjusting the post-test probability accordingly i.e. “a subjective belief should be rationally changed when presented with evidence”. We use this concept routinely in clinical medicine but it is important to understand this context when interpreting likelihood ratios and using diagnostic tests.  It is critical to establish the pre-test probability of disease prior to ordering a diagnostic test and to use the post-test probability when making clinical decisions. 
By: Dr. Lisa Calder