A clinically useful capillary blood-sampling technique for rapid determination of therapeutic levels of theophylline.

Two blood-sampling techniques, capillary and venous, were compared using the EMIT method. No difference was found in reproducibility. However, persistent positive bias of 0.628 micrograms/ml (p less than 0.01) was noted with the capillary sampling method. Any hemolysis that occurred in the capillary sampling technique did not significantly affect the assay.