Effect of drawing blood specimens proximal to an in-place but discontinued intravenous solution. Can blood be drawn above the site of a shut-off i.v.?

To assess the effects of drawing blood specimens from a site proximal to an intravenous (IV) infusion line, 24 volunteers were infused with approximately 30 mL of 5% (w/v) dextrose in 0.9% (w/v) NaCl solution. Specimens were drawn proximal to the IV line, while the solution was infusing, and at 1, 2, and 3 minutes after discontinuance of the infusion and assayed for glucose, sodium, chloride, and red blood cell (RBC) count. Control samples were obtained simultaneously from the opposite arm to determine any residual or dilutional effects from the infusing solution. Statistical analysis using the paired sample t-test showed no significant difference of RBCs between arms at or beyond 1 minute. Statistical power analysis reveals that there is a 95% level of certainty that there is less than 1% dilution of the test arm specimen. Analysis of sodium and chloride levels showed no contamination of the test arm specimen at 1 minute, but glucose concentrations still showed an average elevation over control of 5% at 3 minutes. The authors concluded that the drawing of blood specimens proximal to an IV infusion, 3 minutes after its discontinuance, has a clinically negligable dilutional effect but substances present at relatively high levels in the infused solution may still be detected.