Ratio of reported red-cell folate to lower limit over time. A. Ratio red-cell folate to reference minimum. B. Ratio red-cell folate to laboratory minimum. The reference minimum, dotted line, in panel A is the red-cell folate normal lower limit according to Bates and Lewis (2012). The laboratory minimum, dotted line, in panel B is the low end of the reference range, or a minimum cut-off value, quoted by each laboratory.