Report of Japan Committee for Vitamin Laboratory Standards Proposed Standard for Total Ascorbic Acid Values in Human Plasma

HPLC Procedure as a Reference Method

Abstract

Standard reference ranges for all laboratory test values are mandatory. This study was designed to establish a reference standard for vitamin C (ascorbic acid) levels in human plasma, since the normal range has not been determined in the Japanese population. We standardized plasma ascorbic acid levels and compared three different reference methods: HPLC/EC, HPLC/UV, and the ascorbate oxidase procedure. The reference range was obtained in 54 healthy volunteers (female university students) given a diet containing 200mg of vitamin C per day for three days. Total ascorbic acid levels (ascorbic acid plus dehydroascorbic acid) in plasma were determined before and after administration of the test meal for three days by three laboratories using the above procedures. Although no significant differences were observed in mean ascorbic acid levels among the three laboratories, the standard deviations converged after diet control for three days. In subjects who had lower plasma ascorbic acid levels before the test, the levels increased to more than 0.62mg/dL after intake of 200mg ascorbic acid per day for three days. Since plasma ascorbic acid levels exhibit a Gaussian distribution, the mean±2SD ranges for plasma ascorbic acid levels were standardized from 0.70 to 1.38mg/dL by the HPLC/ECD procedure. There were high correlations in the values obtained by the three different methods. The lower reference levels coincided with the value (i.e., more than 0.7mg/dL) cited in the Recommended Dietary Allowances (DRIs) for vitamin C in the Japanese population.