In a recent trial that was monitored by CTU Bern, lab samples had to be taken within 10 Minutes prior and 2 hours after administration of study drug (i.e. a -10 minutes and a +2 hours sample), and lab results including sampling date and time point had to be recorded in the study database (the eCRF).
For 5 patients that had their visit early in the morning on the same day, it was noted by the monitor that no lab values were recorded in the eCRF for the +2 hour sample while the -10 minutes values were all there as needed.
The study nurse was convinced that she had taken all samples as required but assumed that the +2 hour samples must have been lost somewhere on their way to the central lab although she stated that this was quite unlikely.
As turned out later, she had indeed drawn all samples as required, they were all analysed by the central lab, and results were all available on the lab reports.
What could be the explanation for this mystery?
It’s actually pretty simple: The time points of the lab results that are indicated as “Probenentnahme” (sampling) on the lab reports are not the time point when the samples were drawn but when the tube labels were printed.
The tide of events was the following:
To prepare for the labour intensive early morning visit with the 5 patients, the study nurse had pre-printed the labels for the -10 Minutes samples in the evening before the visit. She then draw the samples at the right time point on the next day, attached the pre-printed labels (that had the date of the day before) to the tubes and sent them for analysis. She then also immediately printed the labels for the +2 hour sample. Two hours after drug administration, she attached the labels (with time point a few minutes before drug administration) on the +2 hour sample.
When completing the eCRF a couple of days later, she recorded the values of the +2 hour samples for the -10 minutes time point, because the lab report misleadingly indicated that sampling was done within the 10 minutes window prior to drug administration. And since on the lab reports, the results for the +2 hours were apparently missing, the corresponding fields in the eCRF were left empty.
Lessons learned?:
Be careful with lab sampling time points in clinical trials, in particular when lab sampling time points are important (and they are in many cases).
In the present case, the study nurse will now record the actual lab sampling time points together with the time point when the label was printed. Since only this will allow her to unambiguously link the results on the lab reports to the samples she actually drew. She will also prepare a note to file to explain that the “Probenentnahme” time point on the lab report is actually the time point when the tube label was printed.