[Difficulties of the microassay of plasma aminoacids (author's transl)]

The difficulties encountered in developing a microassay of plasma aminoacids are presented. Blood was collected by capillary puncture simultaneously at the heel, finger tip and from the lobe of the ear and the results were compared with those obtained from venous blood. Capillary plasma was shown to be contaminated by free aminoacids from the skin, which causes a considerable elevation especially of the serine level. Glycine, ornithine and histidine were also often increased. Our findings suggest that caution is necessary when interpreting aminoacid results estimated on blood collected by capillary puncture.