Folate (Folic Acid) - Medscape Reference

Most commercial laboratories offer the quantitative determination of folate in human serum, plasma, and RBCs using the ARCHITECT chemiluminescent microparticle immunoassay (Abbott) [16] or electrochemiluminescence technology with flexible assay protocols (Roche). Other analytic tools are also available, such as the Immulite immunoassay (Siemens), [17] the Quantaphase II folate/vitamin B12 radioassay kit (Bio-Rad), [18] and the microbiological method. [19] Another analytic technique, using a competitive binding receptor assay (the access folate assay) is available at Mayo Clinic Laboratories. [20]

Specifics of the ARCHITECT and the Immulite systems are listed below.

ARCHITECT folate assay — serum folate level

Specifics for this assay include the following [16] :

• Specimen type: Venous blood
• Container: Serum (glass or plastic tube), serum separator tube, lithium heparin plasma separator tube; do not use plasma in ethylenediaminetetraacetic acid (EDTA) tubes for folate; protect specimen from light; hemolyzed specimens will give falsely elevated levels.
• Collection method: Venipuncture
• Specimen volume: 3 mL
• Collection instructions: Test should be performed after an 8-h fast; avoid vitamin B12 injection, folate-rich diet, or alcoholic drinks before the test. [10]
• Other instructions: Do not use specimens that have been heat inactivated, pooled, hemolyzed, or have obvious bacterial contamination

The following lead to inaccurate results:

• The use of human anti-mouse antibodies
• Routine exposure to animals/animal serum products that have heterophilic antibodies in their serum and can react with reagent immunoglobulins
• The use of methotrexate, aminopterin, or folinic acid (leucovorin)

If testing is not being performed immediately, specimens may be stored at 2-8° C for 7 days or at −10° C for 30 days.

Immulite 2000 folic acid test — RBC folate level

Specifics for this assay include the following [17] :

• Specimen type: Venous blood; calculation of RBC folate requires simultaneous testing of the patient's hematocrit and serum folate level
• Container: Fresh heparinized or EDTA whole blood (EDTA plasma should not be used)
• Collection method: Venipuncture
• Specimen volume: 100 μL fresh heparinized or EDTA whole blood for RBC folate, 50 μL serum/heparinized plasma for serum folate
• Collection instructions: Test should be performed after an 8-h fast; avoid vitamin B12 injection before test
• Other instructions: To clear a lipemic sample, ultracentrifuge use is recommended; ensure complete clot formation prior to centrifugation.

If testing will not be performed immediately, specimens may be stored at 2-8° C for 8 h or at −20° C for 6-8 weeks.