Friday, May 24, 2013
The vapor trail
by Chet Hardin
click to enlarge
Here's a quick primer on the procedure that the Colorado Department of Public Health and Environment has adopted for blood tests, according to Vanessa Simmons, the work lead in the toxicology lab:
The lab receives the blood samples through the mail or by courier. They are checked into a secure storage area. Once the sample is logged in, it's given a barcode that corresponds to its paperwork.
When a sample is analyzed, through a process known as gas chromatography, it's first placed on a rocker to warm it and break up any clogs.
The blood from the individual sample is then pipetted into a vial, with water and n-Propanol, the internal standard used to quantify the test results.
The vial is capped with a stopper, and an aluminum cap crimped over that, and then it is transferred to the Headspace GC, the blood-testing instrument.
The machine pressurizes and heats the sample, creating a vapor. A needle punctures the vial, drawing out the vapor and injects it into the two columns — picture long, bendy straws — in which it will be analyzed.
They run every sample in duplicate, through the two columns, and they can run 40 samples at a time. The whole process for each sample takes about 10 minutes.
"All of the paperwork is generated as the samples are analyzed," says Simmons; these print-outs are called chromatograms. "Once the whole run is completed, which is usually the next day, the paperwork is taken off and reviewed for accuracy, to ensure everything meets our quality-control criteria."
Simmons says the two raw testing numbers from each sample's run have to be within 5 percent of each other; the single "blood alcohol content" number you get in the end is the average of those two raw numbers.
If the raw numbers aren't within 5 percent of each other, but are within 10 percent, either (1) a supervisor can OK the results or (2) the blood is re-tested. If the range is greater than 10 percent, they have to be re-tested.
The paperwork is reviewed by Simmons, or peer-reviewed, then goes to lab supervisor Cynthia Burbach for sign-off.
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