Red Cell Folate Testing

Laboratory Diagnosis of Folate Deficiency

November 2010

Suspicion of folate deficiency may originate if patient history reveals any clinical conditions previously mentioned and/or from results from a routine complete blood count, where a low hemoglobin and high MCV are observed. Use of the MCV alone is a nonspecific indicator when used by itself, as patients with concurrent iron and folate deficiency will not have the characteristic macrocytosis seen in folate deficiency alone. Laboratory diagnosis of folate deficiency further includes measurement of serum folate, and less often red blood cell (RBC) folate, also called erythrocyte folate. In blood 95% of folate is within the erythrocytes. Folate is taken up only by the developing erythrocyte; therefore RBC folate has historically been regarded as the better indicator of long-term folate storage. Serum folate concentrations reflect recent dietary intake of folate, but measurements need to be conducted after the patient fasts. Thus, theoretically, while RBC folate is less susceptible to rapid changes in dietary intake, analytically, the assays are plagued with imprecision issues. As mentioned previously, homocysteine and methylmalonic acid may also be utilized to distinguish between folate and B12 deficiency.

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Laboratory Diagnosis of Folate Deficiency

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Jump to section:

• Introduction
• Folate
• Folate
• Selected Food Sources of Folate and Folic Acid*
• Causes of Folate Deficiency
• Laboratory Diagnosis of Folate Deficiency
• Folate and Vitamin B12 Deficiency
• Quantitation of Folate: Methods
• Differences Between Folate Immunoassays
• Analytical Imprecision: RBC Folate (CAP Surveys)
• Equivalence of Serum and RBC Folate
• Modern Folate Deficiency is Rare
• Mayo RBC/Serum Folate Orders 1999-2009
• Conclusions
• Questions?