What is serum folate
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Understanding Serum Folate: Composition, Measurement, and Clinical Relevance
What is Serum Folate?
Serum folate refers to the concentration of folate compounds present in the blood serum. Folate, also known as vitamin B9, is essential for numerous bodily functions, including DNA synthesis, repair, and methylation, as well as amino acid metabolism. The primary form of folate found in human serum is 5-methyltetrahydrofolate (5MeTHF), which is crucial for methionine biosynthesis 12.
Composition of Serum Folate
Folate Compounds in Serum
Human serum contains various forms of folate, including 5MeTHF, 5-formyltetrahydrofolate (5FoTHF), and folic acid (FA). The predominant form is 5MeTHF, which constitutes approximately 85.8% of the total folate in healthy individuals . Other forms, such as 5FoTHF and FA, are present in smaller quantities 24. Additionally, folate catabolites like p-aminobenzoylglutamate (pABG) and p-acetamidobenzoylglutamate (apABG) are also found in serum, especially in patients with renal failure .
Stability and Degradation
Folate stability in serum can be affected by storage conditions. Long-term storage at -25°C leads to a gradual degradation of 5MeTHF, with a decrease of about 3.2% per year. However, a significant portion of folate can be recovered as pABG equivalents even after decades of storage .
Measurement of Serum Folate
Analytical Methods
Several methods are used to measure serum folate levels, each with its advantages and limitations:
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Microbiological Assays: These assays use microorganisms like Lactobacillus casei to measure folate activity. They are sensitive but can be influenced by the presence of different folate forms 15.
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Radioassays: These involve the use of radioactively labeled folate and folate-binding proteins to quantify serum folate. Radioassays are quick and can provide results within hours, making them useful in clinical settings 710.
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Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS): This advanced method allows for the precise quantification of various folate forms and their catabolites. It is considered a reference method due to its high accuracy and ability to measure multiple folate species simultaneously 469.
Standardization and Variability
The measurement of serum folate can show significant variability across different methods and laboratories. The establishment of an International Standard (IS) for serum folate, such as IS 03/178, has helped reduce this variability. This standardization ensures more consistent and reliable results across different testing platforms .
Clinical Relevance of Serum Folate
Health Implications
Folate status is linked to several health conditions. Deficiency in folate can lead to neural tube defects, certain cancers, cardiovascular diseases, and cognitive impairments . Conversely, elevated serum folate levels can be indicative of certain diseases or conditions, such as liver disease or excessive dietary intake .
Diagnostic and Therapeutic Use
Accurate measurement of serum folate is crucial for diagnosing folate deficiency and monitoring the effectiveness of supplementation therapy. For instance, patients with folate deficiency often show significantly lower serum folate levels, which can be rapidly assessed using radioassays or LC-MS/MS methods 710.
Conclusion
Serum folate is a critical biomarker for assessing folate status in the body. It comprises various forms, with 5MeTHF being the most abundant. Accurate measurement of serum folate is essential for diagnosing deficiencies and monitoring treatment. Advanced methods like LC-MS/MS provide precise quantification, while standardization efforts have improved consistency across different laboratories. Understanding serum folate's composition and measurement is vital for its effective clinical application.
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Most relevant research papers on this topic
International Standard for serum vitamin B12 and serum folate: international collaborative study to evaluate a batch of lyophilised serum for B12 and folate content
The use of International Standard 03/178 for serum vitamin B12 and folate assays significantly reduced inter-laboratory variability and demonstrated satisfactory long-term stability.
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