A Comparison of the Urea Nitrogen Content of Cutaneous and Venous Blood by Micro Gasometric Analysis.

Svensgaard (1) using the micro urea method of Rehberg (2) compared the urea concentrations in blood from the arm vein with that of cutaneous blood from the lobe of the ear. In 29 of 32 analyses of the blood of normal fasting subjects she found the urea of the capillary blood higher thamn that of the venous blood. The average difference was 10 per cent of the venous urea content, but individual differences were as high as 24 per cent. Such results, if confirmed, would indicate that the use of cutaneous blood from the ear for analysis could introduce errors up to 24 per cent in tests of renal function, such as the blood urea clearance used in this clinic (3, 4, 5), which depend upon blood urea determinations. It was therefore thought advisable to make a series of determinations of the urea content of samples of cutaneous and venous blood taken simultaneously and both analyzed by the Van Slyke micro gasometric method (6) in order to ascertain whether the variations found by Svensgaard could be confirmed. A report of the analyses is given in this paper.