Donor Kidney Volume Predicts Graft Survival
MIAMI BEACH, Fla.—Abdominal computed tomography (CT) images from the work-up of kidney donors can be useful in predicting whether their recipients' kidney function is likely to improve significantly after the transplant, according to a new study conducted by researchers at the University of Michigan Health Systems in Ann Arbor.
Data presented at the 13th Annual American Society of Transplant Surgeons' State of the Art Winter Symposium show that patients who receive kidneys from people with relatively large kidney volumes have higher estimated glomerular filtration rates (eGFRs) up to five years post-transplant than recipients of relatively small kidneys. In addition, they have higher eGFRs when the donors have relatively large trunk muscles. Both kidney size and trunk-muscle area can be determined by examining CT images.
The researchers concluded that in the future it may be a good idea to include this information when assessing people who have offered to donate a kidney.
“A potential donor who is 65 years old and appears to be an average risk surgical candidate may in fact have the core muscle size, muscle density, and arterial calcification of a person 15 years older, and accordingly has higher surgical risk on par with that of the average 80-year-old,” said Kara Barnhart, a second-year medical student. “Although further research and validation are still needed, the concept of morphometric age may be able to provide an objective assessment of surgical risk that is intuitive for both clinicians and patients.”
Barnhart conducted the study under the supervision of Michael J. Englesbe, MD, Associate Professor of Surgery. They and five others reviewed computed tomography images and donation outcomes from 302 people who donated kidneys at the University of Michigan between 2000 and 2008. In their analyses, they divided the donors into tertiles of kidney volume and psoas major area. The psoas major is a trunk or “core” muscle that runs from the back of the spine to the front of the pelvis.
The donors' average age was 41.8 years, their mean eGFR was 113.9 ml/min/1.73 m2 and their psoas major muscles' average area was 2,609 mm2. Their average kidney volume was 198.7 cm3. Routine abdominal CT imaging also revealed that about one-fifth of the donors – 17.7% – had aortic calcification, and among those, the average portion of the aortic wall that was calcified was 4.5%.
The recipients' average age was 47.1 years and 40.1% were female. Furthermore, 41.1% had diabetes, 28.9% had coronary artery disease and their mean body mass index was 27.4 kg/m2.
When the investigators examined death-censored graft survival, they observed that neither donor kidney volume nor donor psoas area were significant risk factors for graft loss. However, when they examined post-transplant recipient eGFR, they found that recipients of the largest-tertile kidneys had significantly higher post-transplant eGFRs than did those of the smallest-tertile kidneys, starting at six months post-transplant and out to five years. In addition, recipients of kidneys from donors who had the largest-tertile psoas muscle area had significantly higher eGFRs from six months post-transplant onwards.
Barnhart said the study has several limitations. For example, it was a single-institution, retrospective investigation, and there was potential selection bias because only donors with pre-transplant CT scans were included in the analyses. In addition, aging is a complex process, and there are many other markers of physiological aging that probably should be taken into account in determining the age-related suitability of a potential donor, she noted.
“Future work will require a more comprehensive evaluation with other potential measures to provide a better understanding of this complex relationship,” Barnhart said.