42 CFR § 493.1236 - Standard: Evaluation of proficiency testing performance.
(b) The laboratory must verify the accuracy of the following:
(2) Any analyte, specialty or subspecialty assigned a proficiency testing score that does not reflect laboratory test performance (that is, when the proficiency testing program does not obtain the agreement required for scoring as specified in subpart I of this part, or the laboratory receives a zero score for nonparticipation, or late return of results).
(c) At least twice annually, the laboratory must verify the accuracy of the following:
(1) Any test or procedure it performs that is not included in subpart I of this part.
(d) All proficiency testing evaluation and verification activities must be documented.