by George Taniwaki

As described in an earlier post, my CT scan angiogram shows that my left kidney is larger than the right one. A bit of research on the web shows this is a common occurrence, though I can’t find any data on what proportion of the population has this asymmetry. In severe cases where the smaller kidney does not function correctly, the condition is called unilateral renal hypoplasia, but again, I cannot find an incidence rate. (I do find reference to having only one kidney, called unilateral renal agenesis, and it is estimated to occur in 0.10% to 0.25% of births.)

In transplant surgeries, the larger kidney will remain in the donor (I guess a corollary of “do no harm” is minimize the chance of harm) while the smaller kidney is removed and implanted in the recipient. Immediately after the transplant, the one good kidney in both patients begins to work harder and increases in size to allow greater blood flow. Eventually, each kidney alone should provide about 70 to 80% of the capacity of the original two kidneys. This is more than adequate to live a normal life.

However, in my case, the difference in size between my kidneys is large enough that the surgeon and nephrologist would like to run a test to ensure that my smaller kidney has enough capacity to support the full needs of the recipient on its own. If it doesn’t, I won’t be allowed to donate.

What is it? Split renogram using gamma camera
Why is it needed? Ensures that the smaller kidney has enough capacity for the patient when transplanted
How is it done? A tracer is added to your blood and then a camera records how much flows through each kidney
Preparation None
Test time One hour
Risks None. The amount of radiation used is very small
Discomfort You have to unbutton your pants. You have to stay very still during the 40 minutes the test takes. The test is not painful


I arrive at UWMC today for my fifth hospital appointment. I am to undergo a procedure called a split renal function test, or a split renogram. First, I empty my bladder. Then I drink two cups of water and am given a small dose of radioactive tracer through an intravenous bag fed into my right arm. The tracer, called Tc-MAG3 (which stands for mercapto-acetyl-triglycine chelated with technetium 99, for those who are curious), will be filtered out by the kidney and thus be concentrated there and in my bladder. Technetium 99 has a half-life of only 6 hours, meaning I should not be exposed to too much radiation. Technetium 99 emits low-energy gamma rays that are detected though the use of a gamma camera.

After letting the IV flow for about a minute the operator positions the camera above my abdomen and tells me to lay still for 40 minutes. The camera takes a series of images at a rate of one per second to record the concentration of MAG3 within my abdominal cavity. Apparently, the images taken by the gamma camera will give a more detailed estimate of split kidney function than a CT scan can. (However, I found some articles that say CT scans alone can estimate split kidney function and the results match gamma camera estimates with r>0.9.)


I prepare for the split renogram with an IV in my right arm and my abdomen under the gamma camera. Photo by UWMC staff

After the procedure, I ask the operator if I can get the images on CD. She says yes, but unlike the CT scan, there is a post-processing step involved. A radiologist must select the regions of the image that denote the left kidney, right kidney, and bladder so that the software can calculate the filtration rate. I go to the cashier and pay my $13.50 fee for the CD. But I won’t be able to take the CD home with me, they will need to mail it.

For more information on becoming a kidney donor, see my Kidney donor guide.

[Update1: The CD arrives in the mail on Friday. Blog post here.]

[Update2: Added a summary table.]