Table 5.
Effect of repeated freeze/thawing of open vials on serum folate concentrations1
| Analyte | Serum folate concentration2 | Relative change3 | |||||
|---|---|---|---|---|---|---|---|
| Reference | 1 F/T | 2 F/T | 3 F/T | 1 F/T | 2 F/T | 3 F/T | |
| nmol/L | % | ||||||
| tFOL | 42.9 (38.6, 47.7) | 42.2 (37.9, 46.9) | 42.6 (38.3, 47.4) | 41.5 (37.3, 46.2) | −1.77* (−2.98, −0.54) | −0.83 (−2.05, 0.41) | −3.32** (−4.52, −2.12) |
| 5-MethylTHF | 37.9 (33.6, 42.6) | 37.0 (32.8, 41.7) | 37.0 (32.8, 41.6) | 36.4 (32.3, 41.0) | −2.31* (−3.50, −1.10) | −2.41* (−3.60, −1.20) | −3.94** (−5.12, −2.76) |
| Folic acid | 0.95 (0.77, 1.16) | 0.96 (0.78, 1.17) | 0.99 (0.81, 1.22) | 0.88 (0.72, 1.08) | 1.09 (−2.45, 4.77) | 5.05* (1.37, 8.87) | −7.03* (−10.3, −3.65) |
| MeFox | 1.90 (1.49, 2.43) | 2.06 (1.61, 2.63) | 2.22 (1.74, 2.84) | 2.01 (1.57, 2.57) | 8.05** (4.69, 11.5) | 16.7** (13.1, 20.5) | 5.59* (2.30, 8.98) |
1
Pooled serum samples were subjected to 3 freeze/thawing cycles (2 h/cycle at 22°C) beyond the first thawing to produce a total of 4 results; first result was used as reference; statistical analysis by 1-way repeated measures ANOVA. 5-methylTHF, 5-methyltetrahydrofolate; F/T, freeze/thawing; MeFox, pyrazino-s-triazine derivative of 4α-hydroxy-5-methyltetrahydrofolate; tFOL, total folate.
2
Values are geometric means (95% CI), n = 30
3
Values are percent change (95% Cl) compared to reference
*
0.0001 ≥ P < 0.05;
**
P <0.0001