Sorry, it’s 2am and I misread. The guy I was responding to is too high not too low. Normal range for blood pH is .1 unit, I would disagree that pH varies by 0.2 in normal conditions, 7.2 to 7.4 is a pretty massive difference as you presumably know.

But that’s largely irrelevant to my point, which is that pH is not so stable that it can’t be used for diagnostic purposes. It’s just that it’s not used for the diagnostic purpose that the OP asked about, and the behaviour of tau proteins etc as noted in the reference doesn’t lead me to think that it is likely to be.