Performance Verification Program for the Folate Microbiologic Assay

The performance verification program for the folate microbiologic assay assesses the performance and continued proficiency of regional resource laboratories engaged in public health work. The program uses 40 serum and/or whole blood samples analyzed over the course of one year.

Target participants:

Laboratories engaged in public health work assessing folate status in populations.

Program goals:

Maintain the quality of folate measurements and document continued laboratory proficiency in performing the folate microbiologic assay through an annual performance report.

Featured analytes:

  • Whole blood folate only
  • Serum and whole blood folate

Participant requirements:

  • Receive 40 samples per year and 8 quality control (QC) samples per year
  • Analyze 10 samples and 2 QC samples per quarter in duplicate and return data to CDC after each of the four (4) challenges
  • Receive a brief summary report after each challenge and a comprehensive annual performance report showing the measurement imprecision and the percent difference compared to the CDC CLIA-approved folate microbiologic assay; the annual performance report is valid for one year
  • Alternatively, analyze all 40 samples in duplicate over a shorter period of time for a one-time assessment of method comparability to CDC

About the Folate Performance Verification Program

CDC’s Nutritional Biomarkers Branch (NBB) established the folate performance verification program in 2019. The program provides an independent assessment of analytical performance for laboratories working to determine population folate status. The program complements a larger collaborative project between CDC, the CDC Foundation, the Nutrition International Folate Task Team, and the Bill and Melinda Gates Foundation to develop regional laboratory capacity for the measurement of blood folate levels (Pfeiffer et al., 2018).

The folate microbiologic assay used in the folate performance verification program was selected based on a WHO recommendation (WHO, 2015). It produces comparable data across laboratories when the laboratories use the same key reagents, such as the calibrator and microorganism (Zhang et al., 2018). To facilitate the use of common key reagents, CDC offers assay materials containing common key reagents for epidemiologic use in population surveys.

The performance verification program follows the CLSI EP9-A2 guideline (Clinical Laboratory Standards Institute, 2002) and provides 40 samples per matrix to allow a comprehensive method comparison to the CDC CLIA-approved microbiologic assay. The program assesses the mean difference between the test and the CDC method, as well as the relationship between the two (2) methods across the concentration range. It also provides eight (8) quality control samples to assess multi-day method imprecision. Some of the program materials are pooled serum, while others are single-donor materials.

The performance verification program is voluntary and non-regulatory and does not provide laboratory accreditation. Participation can either be on a one-time basis to assess method performance (e.g., upcoming survey) or on a continuous basis, where the 40 samples are analyzed over the course of one year (e.g., 10 samples per quarter). The program uses objective quality goals based on biologic variation to assess the acceptability of method performance (Fraser et al., 1997).

Shipping and Reporting Schedule

Participating laboratories must be able to receive frozen samples packed in dry ice, retrieve samples from customs at the airport, and pay for any costs required by customs.

Costs of the Folate Performance Verification Program

Participants pay a user fee to cover CDC’s costs for developing program materials. Participants also pay for material shipping costs.

Enrolling in the Folate Performance Verification Program

For additional program and enrollment information, contact Please include the country and/or laboratory name and “Folate MBA performance verification program” in the subject line.


Clinical Laboratory Standards Institute. Method Comparison and Bias Estimation Using Patient Samples (CLSI document EP9-A1). Wayne, PA: Clinical Laboratory Standards Institute. 2002.

Fraser CG, Hyltoft PP, Libeer JC, Ricos C. Proposals for setting generally applicable quality goals solely based on biology. Ann Clin Biochem 1997;34:8–12.

Pfeiffer CM, Zhang M, Jabbar S. Framework for laboratory harmonization of folate measurements in low- and middle-income countries and regions. Ann N Y Acad Sci 2018; 1414:96–108.

World Health Organization. Guideline: optimal serum and red blood cell folate concentrations in women of reproductive age for prevention of neural tube defect. Geneva, Switzerland: World Health Organization, 2015.

Zhang M, Sternberg MR, Pfeiffer CM. 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. J Nutr 2018; 807–17.

Page last reviewed: September 17, 2019