[Stability of alpha-tocopherol: pre-analytical conditions in its determination in blood samples]

Incomplete and controversial data exist concerning vitamin E or alpha-tocopherol stability in biological samples. Recent clinical interest in the protective function of alpha-tocopherol provided another reason for the setting-up of a multicenter study by the Sociéte Française de Biologie Clinique. Our purpose was to examine the effects on alpha-tocopherol stability, firstly, of collection and transportation of blood samples, and, secondly, of the temperature (-20 degrees C and -80 degrees C) and period of storage of serum or plasma. alpha-tocopherol was determined in serum or plasma by isocratic liquid chromatography with UV detection at 292 nm. Our results established that alpha-tocopherol was extremely stable in blood, serum or plasma over 8 hours without special handling conditions (light, temperature). Pools of serum or plasma were stable for at least 3 months at -20 degrees C and -80 degrees C. They are suitable for use in the quality control of alpha-tocopherol. On the other hand, in some samples, we observed great variability in the rate of alpha-tocopherol degradation. However, there was lesser degradation when these plasma samples were stored at -80 degrees C instead of -20 degrees C. We therefore do not advise storing serum or plasma for more than 1 month at -20 degrees C for more than 3 months at -80 degrees C. This latter temperature is recommended in epidemiological studies.