Well black people in the US generally are a mix of central African + European + other. So like any group like that can have genetic factors that predispose them to certain diseases. Besides kidney disease problem people have much higher rates of sarcoidosis. It is what it is.

In this case sounds like dummkopfs decided to adjust the test to normalize black peoples rates of kidney disease to those of white people.

I'll be over here banging my head against my desk.