The MTHFR C677T, APOE, and PON55 gene polymorphisms show relevant interactions with cardiovascular risk factors.

tion in nmol/L and x is the year of collection). In the autoclaved cards, 17-OHP concentrations were 27.3% lower than in the native cards: median (25th–75th percentiles), 5.6 (3.6–8.9) nmol/L vs 7.7 (5.3–11.1) nmol/L; P 0.001. Thus, 17-OHP in dried blood spots on autoclaved or native filter-paper cards decreased 2–3% annually, and the decrease was significant on native cards but not on autoclaved cards. However, given an interassay CV of 8%, this small decrease may be unimportant for interpretation of samples stored for a few years. If samples are kept for a decade or more, however, it may be wise to correct for the loss, certainly at the expense of an increase in the error of estimate. Thus, in a moderate climate such as in Middle Europe, 17-OHP is basically stable in native or autoclaved filter-paper cards stored at room temperature over a prolonged period. The stability of 17-OHP on filter paper for up to 1 year has been ascertained in previous studies (5, 12). Similarly, progesterone has been shown to be stable in filter paper for 15 weeks at 25 °C and for 9 weeks at 37 °C (13 ). Steroids are known to be stable in serum stored at 25 °C for up to a decade (14 ). We conclude that 17-OHP estimates in dried blood on native or autoclaved filter papers stored for more than a decade can reliably be used for retrospective examinations and population studies.