Cautionary wisdom on Cdiff testing

By  |  November 3, 2008 | 

Although most current rapid assays for Cdiff toxin A and B tout very high sensitivity and specificity, the cautionary wisdom elucidated in this study (abstract) is to consider the positive predictive value (PPV) of the test, which depends on the prevalence of the disease in the population you are testing. The authors note that only about 10% of hospitalized patients with diarrhea will have Cdiff. If there are 500 stool samples submitted, even if the sensitivity and specificity of your Cdiff test is 95% and 97%, the PPV is only 78% (which means that 22% of +tests do not represent true Cdiff).  The assays evaluated in this study had median sensitivites from 76-95% and specificities from 93-100%. You can determine the PPV of the cdiff test at your hospital by determining the sensitivity and specificity of the assay, and the # (and % of total) of positive tests .  This will greatly help you interpret your cdiff tests!

About the Author:

Danielle Scheurer
Dr. Scheurer is a clinical hospitalist and the Medical Director of Quality and Safety at the Medical University of South Carolina in Charleston, South Carolina, and is Assistant Professor of Medicine. She is a graduate of the University of Tennessee College of Medicine, completed her residency at Duke University, and completed her Masters in Clinical Research at the Medical University of South Carolina. She also serves as the Web Editor and Physician Advisor for the Society of Hospital Medicine.

Categories

Related Posts

By  | June 29, 2013 |  0
This large systematic review found rectal NSAIDs significantly reduced the risk of post-ERCP pancreatitis compared to pancreatic duct stents (abstract).
By  | June 22, 2013 |  0
This large population-based cohort found the most common causes of drug induced liver injury to be augmentin and diclofenac, followed by herbal and nutritional supplements (abstract).
By  | May 25, 2013 |  0
This large trial of patients with a relative contraindication for enteral feeds were randomized to early TPN or usual care. There were no differences in the groups in 60 day mortality or LOS, but those on TPN did have a shorter time ventilated and less muscle/fat loss. It is unclear based on this trial if […]

One Comment

  1. CArlos Gutierrez MD MSc November 24, 2008 at 11:55 pm - Reply

    It is an amazing job summarizing a paper in just a few words. Congratulations.

    For a test with sensitivity of 95% and specificity of 97%, the PPV is 78% for a pretest probability (“prevalence”) of 10% as you correctly stated. However, 5% +test would “not represent true CDiff” (not 22%), if by this you meant the proportion of false positives.

Leave A Comment