Robustness of the CDC Folate Microbiologic Assay Kit During Simulated Delayed Shipping

Abstract

ObjectivesThe WHO has recommended the accurate and practical microbiologic assay (MBA) to assess population folate status. To help laboratories in low-resource countries conduct folate measurements, the CDC developed a folate MBA kit containing critical reagents: calibrator, microorganism, quality control (QC), and reagent stock solutions to prepare culture medium. Shipping frozen kits internationally is complex and sometimes delayed, potentially causing materials to thaw. We investigated whether refrigerated or ambient kit temperatures affect folate results.MethodsWe conditioned 5-methyltetrahydrofolate calibrator stock solution, L. rhamnosus microorganism inoculation, serum and whole blood lysate (WBL) QC samples, and reagent stock solutions (ascorbic acid, chloramphenicol, and manganese sulfate) at 6°C ≤ 3 d and 20°C ≤ 2 d protected from light; we then compared conditioned vs. optimally stored materials (-70°C) by analyzing serum and/or WBL samples (≥3 runs).ResultsThe conditioned calibrator showed a mean folate difference (range from 3 runs for 43 WBL samples) of −0.3% (−4.0 to 4.1%) at 6°C/3 d and 0.9% (−1.6% to 2.7%) at 20°C/2 d. Similarly, the conditioned microorganism showed a mean difference of 4.3% (0.7% to 8.3%) at 6°C/3 d and 0.6% (−3.5% to 4.9%) at 20°C/2 d. The conditioned reagents showed a mean difference (range from 3 runs for 5 serum and 5 WBL samples) of 0.3% (−7.4% to 9.0%) at 6°C/3 d and 3.6% (0.1% to 9.0%) at 20°C/2 d. The 2 conditioned serum QC samples (∼13 and ∼40 nmol/L) showed a mean difference (range from 6 runs) of −0.6% (−6.0% to 2.3%) at 6°C/1 d, but higher differences of −5.8%, −5.9%, and −20.7% at 6°C/3 d, 20°C/1 d, and 20°C/2 d, respectively. The conditioned low WBL QC sample (∼300 nmol/L) showed small mean differences (−1.5%, −2.4%, −1.7%, and −0.3% at 6°C/1 d, 6°C/3 d, 20°C/1 d, and 20°C/2 d, respectively), while the conditioned high WBL QC sample (∼600 nmol/L) showed higher mean differences (−3.1%, −12.4%, −6.9%, and −23.7%, respectively).ConclusionsAll kit components except for the QC materials demonstrated adequate stability (<5% change) at 6°C ≤ 3 d or at 20°C ≤ 2 d. The QC materials should not be exposed to 6°C for > 1 d to ensure stability. These findings provide important and practical information for kit shipment management.Funding SourcesNone.