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Serum folate forms are stable during repeated analysis in the presence of ascorbic acid and during frozen sample storage
  • Published Date:
    October 12 2018
  • Source:
    J Appl Lab Med. 3(6):993-1002
  • Language:
Filetype[PDF-864.12 KB]

  • Alternative Title:
    J Appl Lab Med
  • Description:

    Serum folate forms and particularly tetrahydrofolate are sensitive to oxidation.


    Using a repeated measures design, we investigated the stability of folate forms in convenience samples with added ascorbic acid (AA, 5 g/L) analyzed initially and after variable (~1–33 weeks) storage time at -70°C. We examined the recovery of tetrahydrofolate added at different spiking levels to serum with and without AA (5 g/L). We also assessed the long-term frozen storage stability of folate forms.


    Repeat analysis produced consistent results with the initial analysis; the mean relative change (95% CI; Lin’s concordance correlation between initial and repeat result; sample size) was 0.08% (-0.24% to 0.39%; rc=0.999; n=301) for 5-methyltetrahydrofolate; 4.23% (2.44% to 6.05%; rc =0.984; n=211) for pyrazino-s-triazine derivative of 4α-hydroxy-5-methyltetrahydrofolate (MeFox); -0.22% (-1.90% to 1.49%; rc =0.986; n=214) for folic acid; and 1.49% (-2.71% to 5.88%; rc =0.889; n=81) for tetrahydrofolate. Linear regression testing for a time trend indicated an estimated average percent change of <±5% for samples retested after 4 months: 5-methyltetrahydrofolate Ptrend=0.0007, folic acid Ptrend <0.0001, MeFox Ptrend =0.38, and tetrahydrofolate Ptrend =0.0256. The mean±SD tetrahydrofolate spiking recovery was 96.7%±9.4% for serum with added AA, but <50% for serum without added AA. We observed ≤10% loss for most serum folate forms during 4 years of storage at -70°C.


    Serum containing added AA showed acceptable stability of folate forms during repeat analysis from the same vial within 4 months, complete spiking recovery of tetrahydrofolate during sample processing, and long-term frozen storage stability of folate forms.

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