The purpose of plotting blood sample counts against time in a plasma volume study is to:

In a plasma volume study, plotting blood sample counts against time serves multiple purposes related to analyzing the behavior of the radiopharmaceutical in the body. One significant reason is to facilitate correction for potential leakage of the radiopharmaceutical.

When a radiopharmaceutical is injected, it should ideally remain within the vascular system for an accurate assessment of plasma volume. Leakage can occur due to a variety of factors, including extravasation or poor vascular integrity, which can affect the concentration of the radiopharmaceutical detected in the blood samples over time. By plotting the counts against time, clinicians can identify inconsistencies or abnormalities in the expected decay pattern or concentration levels that might indicate leakage. This allows for adjustments to be made to ensure that the calculated plasma volume reflects true physiological conditions rather than artifacts from radiopharmaceutical leakage.

While presenting a visual representation of data is useful, the primary focus in this context is on ensuring that interpretations made from the data regarding plasma volume are accurate, especially by correcting for any extraneous factors like leakage. This ensures that clinicians can make valid assessments about a patient’s condition based on the study results.