|Folate in serum||Lit.|
|Method(s): Microbiological assay, using a chloramphenicol resistant strain of Lactobacillus casei. The assay has been adopted to a microtiter plate format and is carried out by a robotic workstation.|
What is measured: Biologically active folate species in serum/plasma. The prevailing folate form in serum/plasma is 5-methyltetrahydrofolate.
|What is measured on the same platform, click here.|
|Performance of the assay|
|Sensitivity, 2 nmol/L; within-day CV (at population median), 4 %; between-day CV, 5 %.|
|Specimen, collection and processing|
|Patient/subject: Serum folate increases after at folate rich meal, and the concentration reflects (in contrast to erythrocyte folate) short-term folate status. Some antibiotics may inhibit growth of Lactobacillus casei, and may cause artificial, low folate levels.|
|Matrix: Serum is preferred because the measured concentration is (about 50 %) lower in EDTA plasma.|
|Volume: Minimum volume is 20 µL, but 120 µL is optimal and allows sample handling and reanalysis.|
|Preparation: The serum concentration of mTHF increases markedly in hemolytic samples, which is explained by release of high amounts of cellular folate into the serum/plasma fraction. Optimal procedure for sample handling involves addition of ascorbic acid and rapid freezing at 80 oC.|
|Folate in serum/plasma is degraded at room temperature, but also in samples frozen at 20 oC. At room temperature and in the absence of ascorbic acid, folate is substantially degraded within days, a process that proceeds faster in EDTA plasma than in serum. In samples stored at 20 oC, there seems to be a decline in concentration (to about 70 %) during the first year, and the concentration is relatively stable thereafter. In some samples stored frozen for years, folate is not detected.
Since mTHF is the prevailing folate species in serum/plasma, the kinetics of the degradation follow that of mTHF, as described for this folate species.
|Transportation; for general instruction on transportation, click here.|
|Frozen, on dry ice.|
|Reference values, interpretation|
|Reference values > 7.5 nmol/L.|