Instructions on appropriate fasting prior to phlebotomy; effects on patient awareness, preparation, and biochemical...

This study investigated the effect of appropriate pre-phlebotomy instructions on patients' awareness of the need to fast, their fasting status at phlebotomy, and the measurement of specific biochemical analytes and indices.

While booking their phlebotomy appointments, two-hundred outpatients, with a wide range of pre-existing medical conditions, were recruited and randomly assigned to either control or intervention groups. The control group received no instructions while the intervention group was verbally instructed to fast for precisely 12 h prior to their appointment. Serum samples were collected from participants to quantify common biochemical analytes and serum indices, some of which were known to be influenced by fasting status, such as triglyceride and the lipaemic index. At the same appointment, participants completed a survey assessing their perception of, and adherence to, fasting requirements.

In the intervention group, 99% responded that they had fasted before phlebotomy vs. 16% of controls. Subjects stated they fasted for 12 h in 51% of the intervention group and 7% of the controls. Median concentrations for potassium and total bilirubin were statistically, but not clinically, significantly different. In the study, a single patient in the intervention group was found to have a lipaemic sample.

Without instruction, it appears few patients will fast appropriately prior to blood collection. This study suggests that most patients recall and adhere to verbal instructions regarding fasting. Though many in the control group stated they did not fast, triglyceride concentration and lipaemia were not significantly different from the intervention group, and biochemical analyses appear unaffected by fasting status.