NeedlesA health care worker hurried in to the ED after being poked with a needle.

‘It was an old 18G needle with dried blood’, she said. Her puncture had drawn blood. You discussed the very low risk of contacting HIV and the side effects of postexposure prophylaxis (PEP). She asked, ‘What does very low risk mean?’

Is there another way to covery risk for patients?

Trick of the Trade

Convey probabilities with everyday risks.

This article uses a risk stratifying tool to convey probabilities that compare to everyday risks such as flying, cancer diagnosis, having an MI, etc. Below is the calculation tool from the paper.


Using this tool, the risk of contacting HIV for this patient would be: 5/ (1000 x 100 x 100) = 1/ 2,000,000

According to the everyday risk table in the article, this is similar to the risk of dying in the next 12 months from lightning. You left her to decide on PEP.

My take

As the author pointed out, the risks cited are probabilities instead of exact measurements. This is an important caveat. I find this helpful to provide context, especially for those who have difficulty deciding on PEP.

Vertesi L. Risk Assessment Stratification Protocol (RASP) to help patients decide on the use of postexposure prophylaxis for HIV exposure. CJEM : Canadian journal of emergency medical care. 2003, 5(1), 46-8. PMID: 17659153

Stella Yiu, MD

Stella Yiu, MD

ALiEM Blog Contributor
Assistant Professor, University of Ottawa Staff Physician, The Ottawa Hospital
Stella Yiu, MD


Emergency physician and clinician educator in Ottawa, Canada. Own opinions. Go #FOAMed!