June 02, 2021
Mayo Clinic has completed a study finding that carefully selected individuals with hypertension can safely donate a kidney. These results, which appeared in the March 20, 2021, issue of Clinical Transplantation, significantly widen the potential kidney donor pool.
Mayo Clinic was the first medical center in the world to accept living kidney donors with hypertension about 20 years ago. Other medical centers followed the Mayo Clinic lead several years later. Naim S. Issa, M.D., a nephrologist at Mayo Clinic in Rochester, Minnesota, and one of the study's authors, says this is the first formal study published with intermediate- to long-term outcomes of donors diagnosed with hypertension.
Dr. Issa is confident the study's results will have an impact. He says members of the public rarely know if they qualify as kidney donors if they have high blood pressure. "They think we will exclude them," he says. "If we now have an increasing donor pool because these individuals qualify, we can get more kidneys to patients who need them. This will save lives."
Previously, transplant physicians worried about transplanting kidneys from individuals with hypertension because of potential future donor health concerns, such as kidney or cardiovascular diseases. They wanted to ensure long-term donor safety while living with only one kidney.
Because of these issues, many transplant centers have considered hypertension an exclusion criterion for transplant. According to a 2021 article in Kidney International Reports, up to half of U.S. transplant centers reject living kidney donors with hypertension.
The Mayo Clinic kidney transplant team researched transplantation of these kidneys because extended-criteria organs could help with the current organ shortage if proved safe and effective.
Currently, the Mayo Clinic criteria for eligible living kidney donors with high blood pressure is strict. Individuals with stage 1 hypertension (blood pressure 130-139/80-89 mm Hg) or stage 2 hypertension (blood pressure 140/90 mm Hg or higher) are allowed to donate a kidney if they meet the following criteria:
- Over 40 years old in whites or over 45 years old in African Americans, as African Americans develop hypertension at an earlier age than whites
- Well-controlled hypertension on a maximum of two medications
- Absence of any target organ damage such as heart disease or proteinuria
- Normal kidney function for age
The Mayo Clinic transplant team does not accept those with severe hypertension, defining patients with hypertension as safe for potential kidney donation if the condition is mild or controlled. "We have to remain very selective, because the first intention is to protect the donor's future health," says Dr. Issa.
After starting to accept living kidney donors with hypertension in 2002, the Mayo Clinic transplant team first published short-term donor follow-up results in 2004. No investigators outside of the Mayo Clinic group observed living kidney donors with hypertension long-term. In the Mayo Clinic study, the investigators followed patients for an average of 10 years.
"This study's results were reassuring," says Dr. Issa. "The donors did well, including all categories of hypertension as defined by the more recent hypertension guidelines. None of the donors had significant kidney disease or went to dialysis."
In the medium- to long-term follow-up, Dr. Issa and the team found that kidney function in donors labeled hypertensive did not differ from kidney function in those labeled nonhypertensive. In addition, the researchers performed biopsies at the time of kidney procurement, in which they noted that patients' hypertension did not cause chronic kidney scarring. He indicates that all donors who had hypertension did fine over time.
Dr. Issa says he's not seen kidney recipients hesitate to receive kidneys from hypertensive donors, especially once they learn patients who have hypertension cannot pass the condition to the transplant recipient.
Dr. Issa points out another factor to consider related to allowing patients with hypertension to donate kidneys: The definition of hypertension has evolved. "In the '50s and '60s, blood pressure in the 160s range or higher was considered normal," he says, adding that the link between elevated blood pressure and increased risk of heart disease was discovered by the Framingham Heart Study researchers in the late 1960s and published in a 1971 issue of American Journal of Cardiology. "Now we use a different and by far lower cutoff to define high blood pressure."
Another aspect of hypertension that has changed over time is the gold standard of blood pressure measurement. Rather than using a brief, in-office, seated measurement with a sphygmomanometer, the Mayo Clinic investigators used the gold standard of blood pressure measurement with an ambulatory blood pressure monitor measuring all 900 trial participants for an 18- to 24-hour period. Dr. Issa mentions that Mayo Clinic is the only medical center to use this measurement to evaluate all potential kidney donors. Therefore, he believes that Mayo has done an optimal job of defining high blood pressure.
In the U.S., the National Center for Health Statistics' FastStats show that 49.6% of adults age 20 or older have hypertension. The risk of the condition increases with age, and Dr. Issa describes hypertension as highly prevalent after age 45.
Geography and ethnicity also play a role: Self-reported data on cardiovascular disease risk captured in the Center for Disease Control and Prevention's Hypertension Maps and Data Sources show that the highest U.S. prevalence is in the South. Dr. Issa notes that rates are highest in states with a higher population of African American and Hispanic individuals, as people of those ethnicities have a higher prevalence of hypertension than do whites.
The evolution of hypertension's definition over time has labeled even more Americans as hypertensive; currently, a 130/80 score marks the beginning of hypertension.
How physicians can help
Dr. Issa suggests that physicians can contribute greatly to finding kidneys for patients in need through education: explaining to loved ones of kidney transplant-eligible patients that even if they, another family member or a friend has hypertension, it is not a barrier to donation.
For more information
Merzkani MA, et al. Renal function outcomes and kidney biopsy features of living kidney donors with hypertension. Clinical Transplant. In press.
Ibrahim, HN, et al. Outcomes of hypertensive kidney donors using current and past hypertension definitions. Kidney International Reports. 2021;6:1242.
Kannel WB, et al. Systolic versus diastolic blood pressure and risk of coronary heart disease: The Framingham Study. American Journal of Cardiology.1971;27:335.
Hypertension. FastStats. National Center for Health Statistics.
High blood pressure. Hypertension Maps and Data Sources. Centers for Disease Control and Prevention.