Do you use PTH levels to help differentiate CKD from AKI in patients who are being evaluated for an elevated creatinine level and who lack long term lab data?  

Never, sounds like a possible tool, but the problem is you may have AKI on CKD. I cannot imagine it is sensitive or specific enough.

Not typically. Might be of some help but not aware that its utility has been examined. I suppose if very high with high Phos and low Ca might be helpful but would not put much weight on it.

Distinguishing between AKI and CKD in the absence of previous labs can sometimes be challenging. Although PTH levels tend to be higher in CKD than AKI patients, PTH levels can increase quickly in AKI, and a substantial portion (25-50%) of AKI patients will have a high PTH level. So, while it may be ...

I do not. I don't believe it is a good differentiating factor. A very elevated PTH likely indicates the presence of CKD for a number of years but it does not exclude the possibility of additional AKI.