Usually donors have be healthy..and ideally free of chronic problems especially Diabetes, cancer, strong family history of renal disease ending on dialysis, and without anatomical abnormalities like Polycystic kidneys.
So we are dealing with a group of healthy people. Consequences of donating may be divided into two...for the ease of explaining..
1. Issues with surgery - The surgery for removing is mostly done laparoscopically these days.(usually left kidney is removed due to ease of removal ). On a recent study in JAMA ,the mortality in the first 90 days is around 3/10,000 patients. Mostly due to bleeding, thromboembolic disease etc. After 1 year the mortality equals the mortality with a comparable healthy cohort.
2. Issues with loss of kidney mass - Since 50% of the nephron mass is lost, its expected that their left over kidney swells up a little to compensate, and creatinine can theoretically double. But usually creatinine goes back to normal or settles within 40% above baseline. The other theoretical risks that need to be watched for over the next 2 years are 1.Hypertension ( not significantly high than in normal population)
2. Protenuria (significance is not really known)
As I mentioned above, the mortality is the same for these people as for someone who has 2 kidneys.
One advantage of donating a kidney is...if in case the donor ends on Dialysis either due to trauma, cancer or CKD), then they will be considered as high priority, and will get transplanted (if they dont have a living donor) within 6 months.
So..go ahead ..encourage patients to donate...if they can...!!!!