The significance of the arterial-venous plasma concentration difference in clearance studies.

Arterial-venous blood or plasma concentration differences and their implications for renal clearance studies are reviewed. In common practice peripheral venous blood or plasma is used for absolute clearance studies employing timed-interval methods following single dosing. However, this is theoretically inappropriate or incorrect because of the systemic arterial-venous blood or plasma concentration difference. Many examples showing arterial-venous differences, together with brief theoretical discussions of factors affecting the differences, are presented. The implications in clearance studies of other organs such as lungs, liver, and the gastrointestinal tract are also discussed.