What is the best preferred injection and blood sample site for a plasma volume measurement?

For plasma volume measurement, the most effective method involves intravenous injection in an antecubital vein, with blood samples taken from the opposite arm. This approach is preferred because the antecubital vein is easily accessible, allowing for a straightforward and clean venipuncture, which minimizes the risk of contamination from the injection site. Taking blood samples from the opposite arm helps ensure that the sample is representative of the plasma volume without any interference that could arise from the injection site, such as volume dilution or local vascular changes due to the injection.

The technique benefits from maintaining separate sites for injection and sampling, which optimizes the accuracy of the measurement by preventing any alterations in plasma concentration that might occur if the sample were drawn from the arm where the injection was made. This method helps ensure that a true baseline plasma volume is measured, making the results more reliable for clinical assessments.

Considering the other options, intravenous injection in a femoral vein might complicate access and increase the risk for complications in a non-urgent setting. Intramuscular injection is not suitable for plasma volumetric measurements as it can lead to variabilities in absorption and distribution compared to intravenous methods. Using a centrally placed intravenous line for injection and fingertip for blood samples also raises concerns about the accuracy and