Who Was Missing From a Study of Blood Tests After Traffic Crashes?
A blood-testing study of injured drivers can describe its participants accurately and still leave important groups out. Brubacher and colleagues tested blood from 1,097 drivers at seven trauma centres in British Columbia. The way the specimens were collected defines the population the results describe.
How the drivers entered the study
The researchers analyzed leftover blood collected for clinical reasons within six hours of a crash. This approach reduced dependence on whether an individual clinician suspected alcohol or drug use. It still required a clinical blood draw within the study window, so injured drivers who were never brought to the participating hospitals or did not have blood collected were outside the sample. The study identified alcohol in 17.8% of the included drivers.
What the study can tell a driver reviewing a result
The percentage describes how frequently the laboratory detected alcohol in the eligible sample. The study did not include a comparison group of drivers who had not crashed. It therefore cannot tell a reader how much alcohol increased the chance of a crash, or whether alcohol caused one driver’s collision.
For an individual result, record the crash time, collection time and any treatment before the sample. Identify the compound reported and whether the result describes an active drug or a metabolite. The study’s overall percentages cannot substitute for those details.
