42 CFR §493.1281

1. (a)If a laboratory performs the same test using different methodologies or instruments, or performs the same test at multiple testing sites, the laboratory must have a system that twice a year evaluates and defines the relationship between test results using the different methodologies, instruments, or testing sites.
2. (b)The laboratory must have a system to identify and assess patient test results that appear inconsistent with the following relevant criteria, when available:
   1. (1)Patient age.
   2. (2)Sex.
   3. (3)Diagnosis or pertinent clinical data.
   4. (4)Distribution of patient test results.
   5. (5)Relationship with other test parameters.
3. (c)The laboratory must document all test result comparison activities.