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Question

Question Posted 08/23/20:
Dear ADNI Team,
I have two questions:
1) I'm working the file UPENNBIOMK10 and wondering what cut-offs you are using for all biomarkers (Elecsys assay, pTau and tTau) I've only have found ABETA42 as 980 pg/ml.
2) is there any file with ABETA42/40 ratio or can I just calculate it by myself? I also can't find the cut-off value for the Abeta42/40 ratio.
I would be very thankful for your help.
Response posted 09/10/20 by Michal Figurski, PhD:
Hello,

In response to your questions:

1. For the Elecsys assay the cut-offs can be established using "mixture modeling" method for Abeta42, or "ROC analysis" for Abeta42, Tau and PTau. For ROC, the endpoints could be:
- CDRsob change to "1" - for the EMCI+MCI group
- study ARM at baseline - between "AD" and "Normal" groups
- Florbetapir >1.11 at baseline
- and so on
2. The ratio is a derived measure, therefore it is not present in the "raw data" files (not part of the instrument output). Please calculate by yourself. The cut-off value for the ratio can be established using the same methods as for Abeta42.

Naturally, you would receive a somewhat different cut-off value using each of the methods. At this time in the Biomarker Core Lab we are using the following cut-off values:
- Abeta42: 980 pg/mL
- Tau: 266 pg/mL
- PTau: 24 pg/mL
- Abeta42/40 ratio: 0.133

Best regards!
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