When medical resources become limited, as in the case of transplantable kidneys, the criteria for deciding who gets the scarce organs change, a national survey found.

In times of scarcity, according to the survey, medical decisions are much more likely to take into account factors such as a patient's prognosis, age and ability to pay.

The survey, based on detailed questionnaires sent to 373 directors of kidney dialysis centers and 80 transplantation directors, was conducted by a medical ethicist at Asbury Theological Seminary and the University of Kentucky in Lexington.

Results were reported in the American Journal of Public Health.

Participants in the study were asked to rate each of 16 possible patient-selection criteria twice -- once for its importance in the current environment and once for its importance if supplies became scarcer.

For example, only 4 percent of the directors would reject a patient for inability to pay if the treatment were unlimited in availability. By contrast, 45 percent would do so if the supply were limited.

Only 10 percent of dialysis facilities currently consider a patient's age in deciding who should get lifesaving kidney dialysis. But if dialysis facilities became limited, 85 percent would consider a patient's age.

"Thus, the elderly stand to lose more than any other group when resources such as dialysis become scarce," said John F. Kilmer, the medical ethicist who conducted the survey.

Medical prognosis -- the length and quality of survival expected -- would become a consideration in nearly every such decision if resources for dialysis and transplantation were limited, the survey found.

Need is likely to outstrip supply for a growing number of high-cost technological advances in medicine -- such as genetic treatments and artificial organs -- forcing society to find ways of selecting patients, Kilmer said.

"Difficult patient selection decisions will inevitably be with us for the forseeable future," he said. "Like the provision of health care itself, the choosing and application of patient selection criteria is a matter of life and death."