We tested 32 human serum samples from DEQAS with prototype Lumipulse 25(OH)D reagents to assess correlations with LC-MS/MS and [sup.125]I RIA.

The program recently began quantitating DEQAS materials with real values assigned by NIST, and is also working on standardizing measurements for 25(OH)D2 and D3, the C-3 epimer of 25(OH)D2 and D3, and 24,25(OH)2D, he said.

The DEQAS also showed that bias of results may be concentration-dependent, and four out of five immunoassays compared had a positive association between bias and 25-OH Vitamin D concentration (2) (Table 1, Figure 1, Figure 2).

Unpublished data from 6 recent cycles of DEQAS were used to test the bias of the most commonly used immunoassays in the scheme relative to the target serum 25(OH)D values as measured by NIST with and without adjustment for measured 24,25[(OH).sub.2][D.sub.3] concentration.

Skorupa, and P Pludowski, "Comparison of two automated serum 25(OH)D assays--experience of pediatric hospital laboratory participating in DEQAS proficiency testing," Postepy Nauk Medycznych, vol.

Inquiring about the DEQAS results and reference standard used will provide meaningful information that they will need before making clinical decisions.

A recent DEQAS investigation (9) has confirmed manufacturers' assertions that 3-epi-25-OH[D.sub.3] is not detected by any of the widely used immunoassays, including the ones used in the Farrell et al.

The International Vitamin D External Quality Assessment Scheme (DEQAS) in the UK has been established for about 20 years with the goal of ensuring the analytical reliability of vitamin D assays.

The College of American Pathologists (CAP) and the UK-based DEQAS (Vitamin D external quality assessment scheme) surveys provide independent approaches to monitor the performance of laboratories that use various methods for testing of 25-OH-D.

In the U.K., an external proficiency-testing scheme for vitamin-D analysis -- termed DEQAS, for vitamin D external quality-assurance scheme -- is available.

Our laboratory has continued to use the calf-thymus receptor method, and is 1 of the last 2 laboratories reporting data with the method to the Vitamin D External Quality Assurance Scheme (DEQAS).

The UK-based Vitamin D Quality Assessment Scheme (DEQAS) has been monitoring the performance of 25(OH)D assays since 1989 and consists of approximately 400 participating laboratories worldwide.