Purpose
The sections below provide responses to the frequently asked questions.
Frequently asked questions for Vitamin D Standardization-Certification Program
Why is the certification process important?
The certification process ensures that the method in question is accurate over time. Many clinical laboratories rely on test manufacturers to maintain certified methods.
What is involved in the certification process?
A manufacturer or clinical laboratory that wants to be involved in the certification process should contact CDC's VDSCP and obtain the protocol.
What materials are used in the CDC standardization programs?
Reference materials used in the programs are prepared from unaltered single-donor human serum, in accordance with CLSI guideline C37-A (Preparation and validation of commutable frozen human serum pools as secondary reference materials for cholesterol measurement procedures; approved guideline).
VDSCP reference materials are stored and maintained frozen, at or below -70°C. Shipments of samples to regions that do not accept dry ice can be arranged. On arrival, the frozen reference material must be immediately transferred to a freezer for storage at -70°C.
Can more than one test be certified with the same set of samples?
To be certified, each test must be enrolled separately and receive its own set of samples.
How long will the certification process take from sending samples to receiving certification?
After meeting acceptance analytical performance for four consecutive quarters, a participant is certified. The certification is valid for one year. After four consecutive quarters, participants are evaluated quarterly for certification.
What are the certification criteria?
The criteria can be found here: Procedures.
When does the certificate expire?
After meeting acceptance analytical performance for four consecutive quarters, a participant is certified. The certification is valid for one year. After four consecutive quarters, participants are evaluated quarterly for certification.
The certificate expires 1 quarter after the date that the laboratory data were compiled and statistically analyzed by VDSCP.
Does VDSCP have a protocol for recertification?
Yes. Participants are encouraged to re-enroll in the program upon receiving certification to prevent gaps in certification status. See program protocol for further information.
Can a clinical laboratory or manufacturer recertify before the previous certificate expires?
A list of certified procedures is updated quarterly, and continuous enrollment is encouraged to remain listed on the website after certificate expiration. To remain on the list and to prevent any gaps between certifications, a participant should plan to re-enroll once certified.
What is the best way to verify that my analytical system has low bias before embarking on a full certification effort?
The best way to verify low bias in an assessment is to perform a comparison with the Vitamin D Reference Laboratory using the 40 patient samples provided in Phase 1 of the program. Phase 1 can be used to assess bias and recalibrate methods as necessary before beginning Phase 2. A more detailed description of Phases 1 and 2 can be found here. Another way is to analyze National Institute of Standards and Technology reference material SRM 972a (Vitamin D metabolites in frozen human serum) that was prepared using Clinical and Laboratory Standards Institute (CLSI) protocol C37-A to minimize matrix effects.
Should my laboratory send in standards or calibrators to be analyzed by the reference method first?
Reference measurement services are offered through VDSCP, but sending standards to be analyzed by the reference method before enrolling it is not necessary. For more information on reference measurement services, contact Standardization@cdc.gov.
If my laboratory has "out-of-control" runs during analysis of certification samples, or if the samples analyzed include "out-of-control" values, can I choose not to report the unusual values?
Laboratories should apply their rules and policies for reporting results. If you have "out-of-control" runs during the certification process, you should investigate the reasons for these deviations before you re-analyze certification samples.