Figure 4. Influence of temperature and freeze/thaw cycles on S-ASM activity in CSF.

A: S-ASM activity of CSF samples stored for up to three weeks at different temperatures (average of three samples). B: Increased S-ASM activity following prolonged storage of CSF samples at −20°C for two months, less change in S-ASM activity following storage at 4°C and decreased S-ASM activity after room temperature storage (average of 12 samples). C: Reduced S-ASM activity by up to 20% following three or more cycles of freezing at −80°C and short thawing at room temperature (average values of six samples). D: Heat-sensitivity of S-ASM in CSF stored at various temperatures as aliquot alone vs. preserved activity in acidic reaction buffer prior to the addition of substrate.