ATC 2012 Report – Functional status could be useful tool in organ allocation

by Thomas R. Collins – The functional status of transplant recipients is a factor that is often overlooked as kidneys are allocated, but may be of value in an effort to get the most use out of them, according to a study presented here at the 2012 American Transplant Congress.

A study out of the University of Pennsylvania found that functional status is an important predictor of survival in all age groups, with the greatest differences seen in elderly patients, said Peter Reese, MD, Assistant Professor of Medicine & Epidemiology at the Perelman School of Medicine at the university.

As the transplant recipient population ages, there are challenges to allocating organs wisely. Older recipients enjoy fewer years of survival on average, compared to younger recipients, with a greater burden of co-morbidities among older recipients.

There is no clear way to best evaluate the global health of older transplant candidates and the best and most fair use of age as a factor in allocation is a topic fraught with controversy.

Functional status might help, though, researchers said.

They linked data from the United Network for Organ Sharing and a database of function scores (SF-36 test) kept by Frenesius Medical Care, a provider of kidney dialysis services and renal care products.

They analyzed a short form of the self-administered SF-36 test, focusing on 10 questions gauging physical function, including assessment of performance of vigorous activities, moderate activities, lifting and carrying groceries, walking, bathing and dressing and other activities.

The retrospective study included a cohort of 19,875 kidney transplant recipients added to the wait list between 2000 and 2006. The median age was 39.

Older patients generally gave themselves poorer marks on the physical function SF-36 questions.

The patients were broken up into four quartiles, according to how they graded themselves on those questions.

Researchers looked at how mortality related to function scores and how mortality related to age group.

They found, as expected, that the lowest-performance quartile corresponded to the worst survival, with a hazard ratio of 1.93. And the age group of 65 and older corresponded to the lowest survival, with a hazard ratio of 3.72.

What was the most telling, though, was comparing the highest functioning quartile with the lowest function quartile within each age group.

The biggest difference between those quartiles was found in the oldest age group. Within that elderly group, aged 65 and up, those with the lowest-function scores had a three-year mortality rate of nearly 30 percent, while those functioning the best had a three-year mortality rate of just 15 percent — a difference of almost 15 percentage points.

In the other age groups, the function levels didn’t account for nearly as big of a difference, with a difference of about seven percentage points or less.

Dr Reese cautioned that while functional status might be important to consider, age remains very important as well.

“Hazard ratios for older age remained very large and only diminished slighly with the addition of functional status,” he said. “Losing sight of chronological age is not helpful.”

They also calculated that functional status’ predictive value was modest — that if only that criterion were used in predicting survival after a kidney transplant, doctors would be wrong about who would live and who would die about 30% of the time.

Dr Reese cautioned that because the SF-36 is self-administered, it might not the best tool for allocation. Plus, older adults might overestimate their functional status, comparing themselves to people their own age rather than to younger people.

Nonetheless, he said, “Functional status is an important and powerful independent predictor of survival in all age groups…. This may be a neglected tool that we could use in a more standardized way.”