Study questions usefulness of ‘rainbow draw’

The majority of extra vials of blood drawn for lab tests are never used, according to a study led by University of Iowa pathology professor Matthew Krasowski, MD, PhD, and published in the journal JAMA Internal Medicine.

Krasowski and Robert Humble, a medical student in the UI Carver College of Medicine, used the UI Hospitals and Clinics electronic medical record system to review six years’ worth of information on the number of extra tubes of blood drawn and how often those tubes were used for add-on testing. Of a total of 370,601 extra tubes of blood that were collected between May 2009 and June 2015, only 7 percent were used for add-on tests, and some tube types were used less than four times out of 1,000.

The researchers hope their data will raise awareness of the problem and help reduce the practice, which is often called the “rainbow draw” because each tube has a different colored top denoting which test the blood will undergo.

“Institutions and providers should reconsider routine use of extra tubes and instead define circumstances where extra tubes are likely to be needed,” Krasowski says. “The take-home message is not that these tubes are never used— that is not the case. But as a routine practice it doesn’t make sense.”