For Registry, EHR, and QCDR providers must have a minimum of one eligible Medicare Part B Patient (regardless of how many Measures you Report) in order to utilize that Reporting Option. There should be one Medicare patient in the denominator of at least one measure (out of the required six). The Medicare patient does not have to be in the numerator (e.g. met the measure).
Example: If one reports 6 measures via EHR, Registry, or QCDR -- one only needs "1" eligible Medicare patient total in order to meet the minimum requirements for the 2018 MIPS Program.
Note: Providers should only choose and report on measures where they have at least one eligible Medicare case that qualifies for the measure. That patient/case does not have to be included in the report for that measure however (as long as you have at least 1 Medicare patient in 1 of your Quality measure reports).
For PY 2018, data completeness criteria is to report on at least 60% of all eligible cases (meet the denominator criteria) for a measure regardless of payer.