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ELI-PGY5 t1_iu4v6gs wrote

Reply to comment by DudoVene in Does the cerebral spinal fluid of people with Alzheimer's have a notably different pH from 'normal' people's? by wrhollin

The normal range for pH is 5 times that. And we see sick or sick-ish people outside that range pretty regularly. Pretty much everyone at my local hospital who gets blood drawn gets their pH checked.

But as to OPs question - my answer is no. We don’t have any simple tests for Alzheimer’s. MRI and PET provide decent info. But if pH on an LP was different, we’d suddenly have a simple, cheap-ish test for the condition.

pH isn’t a useful test on CSF in normal circumstances btw. We do care about pH in other fluids - pleural fluid, vaginal samples, blood etc.

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mirrim t1_iu4wf9y wrote

This is not true. Normal blood pH is 7.35-7.45. A pH of 6.4 or 8.4 would be fatal. The instruments in my lab can't even read lower than 6.8.

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Grogfoot t1_iu50dpc wrote

"Fluids" is pretty broad, and would include things such as urine, which can be quite variable. But, OP and the thread is referring to fluids that would likely be those continuous with blood and would definitely not vary by an entire pH unit!

Typical pH values of blood are ~7.3. A blood pH less than 6.8 wouldn't even be incompatible with life let alone "normal range".

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ELI-PGY5 t1_iu5ei09 wrote

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.

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