Very true. There have been serious consequences of white doctors misdiagnosing serious emergency conditions coz of the skin tone changes related to flushing, hypoxia and other blood flow related color changes that are not readily apparent to the untrained eye when looking at the faces of African American patients.
Yeah, as I understand it, the thing about this variant red-blood-cell thing, is if you inherit genes for the variant from both parents, it's obvious, because it causes a form of anemia (sickle-cell being the most well-known one), but if you only inherit from one parent you end up with _slightly_ wonky red blood cells, that don't cause illness, but apparently _can_ make the HbA1c test come out wrong.
(Which makes me question, slightly, the way they've changed the diagnostic criteria for diabetes to be based on the HbA1c test rather than fasting glucose tests - I hope they know what they are doing and that won't lead to certain ethnic groups being misdiagnosed)
Also, I gather that they recently (in the course of the pandemic, I think) concluded that those finger-worn oxymeters don't always work reliably for black people.