Dataset Information

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.

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.

SUBMITTER: Zhang M

PROVIDER: S-EPMC8479687 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background: Serum folate methods produce different results. The comparability of HPLC-mass spectrometry (MS)/MS methods is not well documented.Objective: We conducted an international "round-robin" investigation to assess the comparability, precision, and accuracy of serum folate HPLC-MS/MS methods.Methods: The CDC laboratory, 7 laboratories with independently developed methods (group 1), and 6 laboratories with an adapted CDC method (group 2) analyzed folate forms in 6 serum pools and 6 calibrators from the CDC (duplicate analysis over 2 d) and in two 3-level reference materials (duplicate analysis).Results: All laboratories measured 5-methyltetrahydrofolate (5-methylTHF) and folic acid; some measured additional folate forms. The geometric mean (range) concentrations (nanomoles per liter) for 5-methylTHF in the 6 serum pools were 18.3 nmol/L (CDC), 13.8-28.9 nmol/L (group 1), and 16.8-18.6 nmol/L (group 2); for folic acid the concentrations were 3.42 nmol/L (CDC), 1.09-4.74 nmol/L (group 1), and 1.74-2.90 nmol/L (group 2). The median imprecision (CV) for 5-methylTHF was 4.1% (CDC), 4.6-11% (group 1), and 1.7-6.0% (group 2); for folic acid it was 6.9% (CDC), 4.9-20% (group 1), and 3.9-23% (group 2). The mean ± SD (range) recovery of 5-methylTHF spiked into serum was 98% ± 27% (59-138%) for group 1 and 98% ± 10% (82-111%) for group 2; for folic acid it was 93% ± 29% (67-198%) for group 1 and 81% ± 16% (64-102%) for group 2. The mean relative bias for 5-methylTHF compared with the reference material certificate value was 12% (CDC), -24% to 30% (group 1), and -0.6% to 16% (group 2); for folic acid it was 73% (CDC), -47% to 578% (group 1), and -3.3% to 67% (group 2).Conclusions: For 5-methylTHF, group 2 laboratories demonstrated better agreement and precision, less variable spiking recovery, and less bias by using a reference material. Laboratory performance for folic acid was highly variable and needs improvement. Certified reference materials for serum folate forms and total folate are needed to improve method accuracy.