pTau217 testing - variations depending on lab?
I have been using pTau217 in serum increasingly this year, for patients presenting with mild cognitive impairment. My understanding is that test has a much better sensitivity / specificity profile than previous serum biomarkers for AD. It's much easier to perform a serum test than do LP / PET on every patient. Consequently I am picking up a lot more mild AD than I was in years past.
It has recently come to my attention that there are a few different labs performing the pTau217 assay. Thusfar I've been asking patients to get their serum drawn by our local hospital lab, which sends referral labs to Mayo. I've been assuming the Mayo lab is accurate and reliable, but my impression is only based on Mayo's reputation. One recent patient's serum was sent to Labcorp, and their cutoff for abnormal is 0.18pg/mL. The report includes the disclaimer "Test 484391 p-tau217 was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration."
My question for the cognitive neurologists out there is: Is there variable reliability with pTau217 testing depending on which lab performs the test? Are Labcorp results as reliable as Mayo's?
Also, are you following up abnormal results with additional confirmatory testing (CSF / PET) when considering anti-amyloid therapies, or is a positive pTau217 in serum enough to justify AAT for MCI patients?