An Analogy: Seatbelts
Consider two studies designed to test the effectiveness of seatbelts in reducing motor vehicle deaths.
Study 1: sample (n)=drivers equipped with seatbelts.
Study 2: sample (n)=drivers wearing their seatbelts.
With seatbelts that have been proven to provide adequate safety restraint, drivers who were mandated to wear their seatbelt in Study 2 would likely produce a higher rate of reduction.
In Study 1, in which drivers have access to but must choose to use their seatbelt, voluntary compliance is tested. Assuming some drivers will not wear the seatbelt, Study 2 would produce a lower rate of reduction.
However, in the real world, where people have choices, only Study 1 accurately represents the impact of seatbelts given human factors.
Making Sense of Initial Specimen Diversion Study Data
Three factors influence the efficacy of diversion technology in reducing contaminated blood culture (CBC) rates:
- Sample Definition
The percent reduction in CBCs is dependent upon the definition of the study sample.
- When n= blood cultures drawn with the diversion device, the resulting “perfect-world rate” reflects how well the device works when used.
- When n = ALL blood cultures collected, the resulting “real-world rate” reflects how the introduction of the device impacts clinical care. All results are calculated inclusive of collections with and without the diversion device. This real-world rate factors in the level of caregiver compliance achieved.
- Method Inclusion
Reduction rates are also impacted by the inclusion of various methods of blood sample collection: direct venipuncture, syringe draws, and peripheral IV catheter. A real-world rate includes cultures taken by all methods, while a perfect-world rate may include only samples taken by direct venipuncture. The gap between these two rates may signify an opportunity to enforce compliance with the hospital’s existing blood culture collection policy. And, although perfect-world rates trend higher than real-world rates, they may not represent an accurate metric for clinical nor financial impact of diversion technology. Accurate measurement requires the inclusion of all blood culture collection methods.
- Environmental Control
When diversion compliance is heavily policed, CBC rates decline further than when clinicians autonomously chose when to use the technology. To be effective in clinical practice, a specimen diversion device must perform consistently and present no operational challenges for the clinician, fitting seamlessly into the standard blood culture collection procedure.
With each new study, ask yourself the following questions…
- Does the study include all collections or only collections using the device?
- Does the data include collections by all methods or a subset of methods?
- Was caregiver practice monitored/guided beyond routine levels?