July 31, 2006 -- Kidney donors appear to have higher than expected blood pressure years after donation, according to an analysis of the existing research.
The findings suggest kidney donation is associated with a slight, but potentially significant, long-term increase in pressure.
However, researchers say better studies are needed to confirm this link and to adequately counsel donors about any potential risks.
"The 48 [reviewed] studies of living donors varied greatly in rigor, methods of blood pressure assessment, and conclusions about whether donation increases blood pressure and the subsequent risk for hypertension," the researchers wrote in the Aug. 1 issue of the Annals of Internal Medicine.
Little Follow Up
Currently, 67,000 Americans with ailing or failed kidneys await transplants.
Only 16,477 kidney transplants were performed in 2005, with 6,896 involving living donors, according to figures from the United Network for Organ Sharing.
More than 80,000 people have donated kidneys worldwide. Medical ethicist James F. Childress, PhD, says the lack of medical follow-up of these donors has made assessment of long-term risks impossible.
Childress chaired a committee on organ donation sponsored by the National Academy of Science's Institute of Medicine. The committee focused mainly on ways to increase the available pool of organs from deceased donors.
But in its report, published last May, it also called for "a careful review and assessment" of the practice of living donor transplants.
"We don't have a registry of living donors or any long-term follow-up in any meaningful sense," Childress tells WebMD. "How can potential donors give voluntary informed consent when we don't have enough information to tell them what they need to know?"
Blood Pressure Rise
In the newly published analysis, researchers reviewed 48 studies involving 5,145 living kidney donors from 28 countries. Their average age was 41 immediately before donation.
Before donation, the donors' average systolic blood pressure (the top number of a blood pressure reading) was 121 mm Hg, and their average diastolic reading (the bottom number) was 77 mm Hg.
A blood pressure of less than 120 mm Hg systolic and 80 mm Hg diastolic is considered normal by most guidelines, including those of the American Heart Association.
High blood pressure is defined as having a systolic pressure of 140 mm Hg or higher or a diastolic pressure of 90 mm Hg or more.
The researchers found that among donors followed at least five years (range: six to 13 years), both systolic and diastolic pressures were approximately 5 mm Hg higher than would have been expected with normal aging.
It has been suggested that every 10 mm Hg increase in systolic blood pressure and every 5 mm Hg increase in diastolic blood pressure is associated with a 1.5-fold increase in death from heart attack and stroke.
"Whether an increase in blood pressure from kidney donation is similarly prognostic requires further consideration, because closer surveillance and early intervention in otherwise healthy adults could offset any such risk," researcher Neil Boudville, MD, and colleagues wrote.
They said counseling potential kidney donors who have a history of high blood pressure poses a particular challenge.
And they concluded that "it remains prudent to counsel and follow all donors, regardless of the pre-donation health state, to manage risk factors in an attempt to prevent hypertensionand future cardiovascular disease."