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The loss of 5-methyltetrahydrofolate in human serum under suboptimal preanalytical conditions can only partially be recovered by an oxidation product1,2,3
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Sep 17 2014
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Source: J Nutr. 144(11):1873-1879.
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Alternative Title:J Nutr
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Description:Background
Maintaining folate stability during sample handling is important, yet challenging.
Objective
We investigated the effects of suboptimal preanalytical conditions on serum folate stability.
Design
Using an HPLC-tandem MS method we measured folates [5-methyltetrahydrofolate (5-methylTHF), folic acid, and MeFox (5-methylTHF oxidation product), minor forms at or below limit of detection] in human serum exposed to suboptimal conditions.
Results
Whole blood samples (n = 21) stored at 32°C for ≤3 d (experiment 1 – delayed processing) showed significant decreases in serum total folate [(tFOL; sum of folate forms) 11–32%, 5.5–15.9 nmol/L] and 5-methylTHF (36–62%, 14.5–25.1 nmol/L) and a significant increase in MeFox (346–415%, 7.17–8.63 nmol/L). Serum samples (n = 21) stored at 11°C for 7–14 d (experiment 2 – delayed freezing) also showed significant decreases in tFOL (4.6–10.4%, 2.3–5.1 nmol/L) and 5-methylTHF (8.4–29%, 3.4–11.6 nmol/L) and significant increases in MeFox (88–320%, 1.82–6.62 nmol/L). The molar loss in 5-methylTHF exceeded the gain in MeFox in these 2 experiments. When we exposed 3 serum pools (tFOL 16.7–58.3 nmol/L) for 24 h to 37°C elevated temperature (experiment 3), the significant decrease in 5-methylTHF (33% on average) was compensated by an equimolar gain in MeFox. Repeated freeze/thawing (≤3 cycles) of serum [closed (experiment 4) and open (experiment 5) vials] showed generally stable folates with small (<1 nmol/L) changes. Long-term (≤12 mo) exposure of 3 serum pools (tFOL 17.5–63.7 nmol/L) to suboptimal (−20°C) freezing temperature (experiment 6) showed significant decreases in tFOL (5% on average) already after 3 mo. The molar loss in 5-methylTHF exceeded the gain in MeFox. Folic acid generally showed good stability.
Conclusions
To avoid folate losses, unprocessed whole blood should be protected from elevated temperature and serum should not be refrigerated for >2 d or long-term stored at −20°C.
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Pubmed ID:25332487
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Pubmed Central ID:PMC5332148
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