Harmonizing the Calibrator and Microorganism Used in the Folate Microbiological Assay Increases the Comparability of Serum and Whole-Blood Folate Results in a CDC Round-Robin Study. Issue 5 (2nd May 2018)

• Record Type: Journal Article
• Authors: Zhang, Ming; Sternberg, Maya R; Pfeiffer, Christine M
• Is Part Of: Journal of nutrition. Volume 148:Issue 5(2018)
• Page Start: 807
• Page End: 817
• Publication Date: 2018-05-02
• Subjects: Lactobacillus rhamnosus -- 5-methyltetrahytrofolate -- folic acid; Nutrition -- Periodicals; Diet -- Periodicals; 613.205
• DOI: 10.1093/jn/nxy030
• Languages: English
• ISSNs: 0022-3166

Abstract

Abstract: Background: Harmonizing critical reagents for the folate microbiological assay (MBA) may improve among-laboratory comparability. Objective: We assessed the comparability of the MBA for serum folate (S-FOL) and whole-blood folate (WB-FOL) in an international comparison study. Methods: Eight laboratories obtained a kit containing CDC microorganism inoculum (chloramphenicol-resistant Lactobacillus rhamnosus ), CDC calibrator (5-methyltetrahydrofolate), and 23 serum and WB hemolysate samples each. Laboratories analyzed the samples in single measurement over 2 d using 4 conditions: in-house microorganism and in-house calibrator (IH-MO & IH-CAL), in-house microorganism and CDC calibrator (IH-MO & CDC-CAL), CDC microorganism and in-house calibrator (CDC-MO & IH-CAL), and CDC microorganism and CDC calibrator (CDC-MO & CDC-CAL). We calculated geometric mean concentrations for each laboratory and condition and compared data to the CDC MBA (target). Results: The among-laboratory arithmetic mean S-FOL concentrations for the 4 conditions were 30.2, 28.1, 30.0, and 29.9 (group 1, 5-methyltetrahydrofolate IH-CAL) compared with 35.3, 33.3, 33.6, and 30.7 nmol/L (group 2, folic acid IH-CAL), respectively; and 428, 405, 398, and 393 (group 1) compared with 469, 423, 477, and 418 nmol/L (group 2), respectively, for WB-FOL. Differences to the CDC MBA target values were smaller for group 1 (range across conditions; S-FOL: 9.9–21%; WB-FOL: 9.0–18%) compared with group 2 laboratories (S-FOL: 13–30%; WB-FOL: 16–32%) and smaller when CDC reagents were used compared with in-house reagents (S-FOL: 12% compared with 22%; WB-FOL: 13% compared with 25%). A linear mixed model estimated a small microorganism effect (S-FOL: 2.3%; WB-FOL: 2.3%) and a larger mean calibrator effect; folic acid compared with 5-methyltetrahydrofolate calibrator produced 12% higher S-FOL and 15% higher WB-FOL results. When laboratories used CDC reagents, the estimated among-laboratory variability was ∼10% for S-FOL and WB-FOL. Conclusion: Harmonizing the calibrator and microorganism for the folate MBA has the potential to improve the among-laboratory comparability in future surveys.