CDC's Vitamin A Laboratory-External Quality Assessment Program Shows Little Change in Laboratory Performance for Multiple Nutritional Biomarkers over a 10-Year Period (2008-2017)

Background: The Vitamin A Laboratory-External Quality Assessment (VITAL-EQA) program operated by the CDC provides analytical performance assessment to low-resource laboratories conducting serum vitamins A (VIA), D (VID), B-12 (B12), and folate (FOL), as well as ferritin (FER) and CRP measurements for public health studies.

Objectives: We aimed to describe the long-term performance of VITAL-EQA participants from 2008 to 2017.

Methods: Participating laboratories received 3 blinded serum samples biannually for duplicate analysis over 3 d. We assessed results (n = 6) for relative difference (%) from the CDC target value and imprecision (% CV) and conducted descriptive statistics on the aggregate 10-year and round-by-round data. Performance criteria were based on biologic variation and deemed acceptable (optimal, desirable, or minimal performance) or unacceptable (less than minimal performance).

Results: Thirty-five countries reported VIA, VID, B12, FOL, FER, and CRP results from 2008-2017. The proportion of laboratories with acceptable performance ranged widely by round: VIA 48%-79% (for difference) and 65%-93% (for imprecision), VID 19%-63% and 33%-100%, B12 0%-92% and 73%-100%, FOL 33%-89% and 78%-100%, FER 69%-100% and 73%-100%, and CRP 57%-92% and 87%-100%. On aggregate, ≥60% of laboratories achieved acceptable differences for VIA, B12, FOL, FER, and CRP (only 44% for VID), and over 75% of laboratories achieved acceptable imprecision for all 6 analytes. Laboratories participating continuously in 4 rounds (2016-2017) showed generally similar performance compared to laboratories participating occasionally.

Conclusions: Although we observed little change in laboratory performance over time, on aggregate, >50% of the participating laboratories achieved acceptable performance, with acceptable imprecision being achieved more often than acceptable difference. The VITAL-EQA program is a valuable tool for low-resource laboratories to observe the state of the field and track their own performance over time. However, the small number of samples per round and the constant changes in laboratory participants make it difficult to identify long-term improvements.