Measurement of blood serum cyclosporine levels using capillary "fingerstick" sampling: a validation study

Capillary blood sampling as a means of monitoring blood cyclosporine levels has replaced venipuncture in some medical centers. As the validity of capi llary venipuncture for analysis of cyclosporine has not been documented, we sought to validate the capillary blood collection technique by comparing i t with serum samples collected simultaneously by venous phlebotomy. Forty p aired capillary- and venous samples were collected from 36 cardiac transpla ntation patients and analyzed, using a polyclonal immunoassay. The values o btained were compared using regression correlation The correlation coeffici ent for all 40 samples was 0.859. However, we discovered that the first 7 c apillary specimens were processed incorrectly. The correlation coefficient for the other 33 samples was 0.995 (99 % confidence interval 0.987-0.998), The excellent correlation between serum samples obtained from capillary sam pling and from venous sampling, together with the ease of obtaining capilla ry blood specimens, make "fingerstick" sampling the method of choice for mo nitoring cyclosporine levels in infants and children.