Patient cards: storage and input for medical data.

The literature concerning the diffusion of innovations reveals that it is not surprising that a promising technology is confronting obstacles in its development and implementation. Alternative technologies also often appear that address the same or similar problems. Better information enables physicians to provide medical care that is less expensive and less error prone. The prescription of medications is reduced in number and cost when the prescribing physician knows the current and previous medications of the patient. The ordering of clinical tests is reduced in number and cost, and the ordering of timely retesting is more likely when physicians have before them information about previous testing of their patient. The challenge is in how the portability of the patient card and its ability to be self-contained can enhance medical practice.