What does african american glomerular filtration rate in a blood test stand for?

Their GFR. Glomerular filtration rate is a test that tells how well the kidneys are doing their job. That is, how well/how fast they clear out fluid from the blood stream, which has impurities in it. African americans tend to have a different rate than the rest of the population, hence the designation in a blood test, since it is a more clear indication of how well their kidneys are doing.