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Question Posted 09/18/23:
The DX_bl variable in ADNIMERGE provides the screening diagnosis for ADNI subjects; however, this dataset excludes subjects who were screened out. Is there a table that gives a consistent diagnosis for subjects in ADNI and also includes screened-out subjects?

Thank you for your help!

Response posted 09/19/23 by Adam Diaz:
The diagnostic summary table (DXSUM_PDXCONV_ADNIALL) available on the IDA contains comprehensive diagnostic information, but getting it out of the table isn't the most straightforward process.

Diagnosis has been recorded in three different fields across the ADNI phases:


The coding is straightforward in ADNI1 and ADNI3:

1 = CN
2 = MCI
3 = Dementia

For ADNIGO and ADNI2, the DXCHANGE variable records diagnostic progression relative to the previous visit, so it needs to be re-coded to be consistent with the other fields. As it stands, the variable is coded as follows:

1=Stable: NL; 2=Stable: MCI; 3=Stable: Dementia; 4=Conversion: NL to MCI; 5=Conversion: MCI to Dementia; 6=Conversion: NL to Dementia; 7=Reversion: MCI to NL; 8=Reversion: Dementia to MCI; 9=Reversion: Dementia to NL

To harmonize this with the other diagnostic status variables, it can be re-coded as follows:

{1,7,9} = CN
{2,4,8} = MCI
{3,5,6} = Dementia

You may also want to distinguish between participants who were screened out, and participants who were lost to follow-up between screening and their initial visit. In this case, screen fail status and reason for exclusion can generally be found in the INCLUSION and EXCLUSION tables. For some edge cases, this information may be scattered across various enrollment-related tables such as additional comments or the protocol deviations log.

If you are interested specifically in diagnostic status, then you may want to exclude participants who were screened out for particular reasons - for instance, the presence of non-AD dementia - which is indicated in INCLUSION/EXCLUSION, as well as in the diagnostic summary table.

Thanks for your question, and please feel free to reach back out if anything is unclear or if you have any other questions.
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