Hang on to your hats because this gets a little complicated. I am NOT a medical professional so this is just for information and referral to other sources. Please consult a medical professional if you have this issue or are curious about it.
Glomerular filtration rate (GFR) is a test used to check how well the kidneys are working. Specifically, it estimates how much blood passes through the tiny filters in the kidneys, called glomeruli, each minute. Older people will have lower normal GFR levels, because GFR decreases with age. Your age, race and gender are factors in determining what is normal. The traditional stages of kidney disease as defined by GFR:
OK, are you with me so far?
My GFR saga began one day a few weeks ago when my doctor called me. She didn’t like my GFR number–it was too low–so she wanted me to re-test but without fasting beforehand. Her theory was that maybe I hadn’t had enough fluids before the test. So…I re-tested and the GFR rate was still too low. Technically, my number falls in the stage 3 Chronic Kidney Disease (CKD) range. Well that sounds scary.
Her next sentence made me freak out a little. “We want to ultrasound your kidney.” EEEK. I pulled myself together and started to think. My doctor is great and I am glad she is vigilant, but general practitioners don’t always understand what a nephrologist would. Maybe we should talk to the kidney people. So she called my coordinator at University of Michigan. In the meantime I work at a library so I got my hands on as much as I could about GFR rate. A lot of what I read indicated that the GFR rate will go down for kidney donors but this doesn’t necessarily mean that your kidneys are failing. Often it will go down then back up. It is an estimated number. Also, you need to look at it in relation to other measures such as albumin and proteinuria levels, your blood pressure and blood glucose.
My other kidney numbers are normal so my transplant coordinator advised to re-test in a year. I am taking this seriously, but I don’t think I am in chronic kidney failure. If kidney donors were experiencing kidney and heart disease in great numbers as a result of low GFR rates, we would have heard about this by now. Many kidney donors experience a drop in GFR, and there is some discussion that there is a need to re-classify these numbers for kidney donors.
All pretty confusing. The lessons from this I think are: Get your kidney panel tests done yearly. General practitioners (not their fault, just the nature of medicine) don’t always know enough about kidney issues so consult a nephrologist or your transplant coordinator if the numbers aren’t normal. Don’t assume that you have CKD but don’t ignore your numbers either. Read as much as you can. Some helpful sources for me were:
- NKF KDOQI Guidelines
- Medline Plus GFR
- Frequently Asked Questions About GFR Estimates
- Does Reduced Glomerular Filtration Rate Equate to Chronic Kidney Disease? BMJ 2012;344:e1167
- CKD Develops in Many Living Kidney Donors
- What low GFR Means for Kidney Donors
- Living Donors Online Message Board