VDSCP: FAQs

Why is the certification process important?

The certification process ensures that the method in question is accurate and reliable. Ongoing certification also assures end users that the product stays accurate and reliable. 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 pdf icon[PDF – 661 KB].

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 the certificate?

The time needed to complete the certification process depends on several factors:

  • How long it takes participants to receive their samples
  • How long it takes to complete the analytical runs
  • How long it takes to meet analytical performance criteria for four consecutive quarters

Given the variables involved, the entire process would take 1 year in the best-case scenario.

What are the certification criteria?

The criteria can be found here: Procedures

When does the certificate expire?

The certificate expires 1 year 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 once certified to prevent gaps in certification. See the program protocol pdf icon[PDF – 661 KB] 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 972aexternal icon (Vitamin D metabolites in frozen human serum) that was prepared using Clinical and Laboratory Standards Institute (CLSI)external icon 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. However sending standards to be analyzed by the reference method before enrolling it is not necessary. For more information on reference measurement services, contact us at Standardization@cdc.gov.

Can CDC’s VDSCP assign values to samples provided by my laboratory?

We work on meeting these requests, but such services are subject to availability of resources. For more information on reference measurement services, contact us at 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?

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 (if volume allows). Laboratories are encouraged to test CDC’s samples in duplicate over 2 days, for a total of four measurements per patient sample, to minimize imprecision.

What materials are used in the CDC standardization programs?

Reference materials used in the programs are prepared from unaltered single-donor human serum according to 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. All such materials are shipped to domestic participating laboratories by air mail. They are shipped in special insulated containers with sufficient dry ice to last at least 48 hours. Additional dry ice is added, as permitted, for delivery to international participants. Shipment of samples to countries 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.

Page last reviewed: July 6, 2017