What is the preferred injection and blood sampling site when performing a plasma volume?

The preferred approach for performing a plasma volume study involves giving the injection in one arm and drawing blood from the opposite arm. This method minimizes contamination of the blood sample with the injected material, providing more accurate results in evaluating plasma volume.

When the injection and blood sampling are performed from the same site, as in some of the other options, there's a risk of altering the concentration of the tracer in the sample due to recirculation or mixing, which could lead to inaccurate measurements of plasma volume. By injecting in one arm and sampling from the opposite arm, there is a clear separation that helps maintain the integrity of the sample collected for analysis.

This approach is essential for ensuring that the data gathered reflect the true plasma volume without interference from the injected substances.