Table 3.
Effect of delayed freezing of serum stored at 11°C for up to 14 d on serum folate concentrations1
| Analyte | Serum folate concentration2 | Relative change3 | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Reference | 2 d | 7 d | 10 d | 14 d | 2 d | 7 d | 10 d | 14 d | |
| nmol/L | % | ||||||||
| tFOL | 49.5 (40.8, 60.1) | 48.8 (40.2, 59.3) | 47.2 (38.9, 57.3) | 47.2 (38.9, 57.2) | 44.4 (36.6, 53.8) | −1.33 (−3.23, 0.61) | −4.61** (−6.45, −2.74) | −4.70** (−6.45, −2.82) | −10.4** (−12.1, −8.59) |
| 5-MethylTHF | 40.3 (34.5, 47.1) | 39.6 (34.0, 46.3) | 36.9 (31.6, 43.1) | 34.6 (29.6, 40.4) | 28.7 (24.6, 33.5) | −1.70 (−5.00, 1.70) | −8.43** (−11.5, −5.26) | −14.2** (−17.1, −11.2) | −28.9** (−31.3, −26.5) |
| Folic acid | 2.21 (1.11, 4.39) | 2.12 (1.06, 4.21) | 2.04 (1.02, 4.05) | 2.09 (1.05, 4.16) | 2.11 (1.06, 4.20) | −4.08* (−7.13, −0.94) | −7.70** (−10.6, −4.68) | −5.27* (−8.27, −2.17) | −4.25* (−7.28, −1.11) |
| MeFox | 2.07 (1.68, 2.55) | 2.45 (2.00, 3.02) | 3.89 (3.16, 4.78) | 5.57 (4.53, 6.85) | 8.69 (7.07, 10.7) | 18.5* (4.70, 34.2) | 87.8** (65.8, 113) | 169** (138, 205) | 320** (271, 375) |
1
Serum from promptly processed whole blood frozen at −70°C was used as reference; statistical analysis by 1-way ANOVA. 5-methylTHF, 5-methyltetrahydrofolate; MeFox, pyrazino-s-triazine derivative of 4α-hydroxy-5-methyltetrahydrofolate; tFOL, total folate.
2
Values are geometric means (95% CI), n = 21
3
Values are percent change (95% Cl) compared to reference
*
0.0001 ≥ P < 0.05;
**
P <0.0001