We recently implemented a procalcitonin assay in my lab in the evaluation of patients with clinically suspected sepsis with undifferentiated infections. How timely then that lead author Yahya Shehabi and members of the ProGUARD study group of the Australian and New Zealand Intensive Care Society (ANZICS) published quite interesting findings from a randomized prospective single-blind study of the use of procalcitonin to guide antibiotic decisions in ICU patients. This article was published in the November 15, 2014 issue of the American Journal of Respiratory and Critical Care Medicine.
One of the challenges in bringing this test online is determining an appropriate cut-off value for "rule-out." The authors report their results using an algorithm with a low cut-off but show that it did not achieve the desired endpoint of reducing antibiotic duration. The study did show, however, that the decline rate in log(PCT) over the first 72 hours independently predicted hospital and 90-day mortality.
In a personal communication with the lead author, Dr. Shehabi confirmed that this lower cut-off was used across different commercially available test methods (including the one we are using) that were used at the different participating centers.
If you are using or plan to implement procalcitonin in your facility, I highly suggest you review this paper.