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January 2011 Clinical Laboratory News: Commercial Assays for Folate


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January 2011: Volume 37, Number 1


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Table 2
Commercial Assays for Folate

Instrument
Method
Type
Immobilization (I) 
Folate Conjugate (FC)
Detection
Calibrator
LOD
Diluent
Sample
Type
Volume
Abbott Diagnostics
Architect NC
HET		 I: FBP immobilized to paramagenetic particles
FC: Pteroic acid labeled with acridinium		 CL PGA in HSA 
Standardized to NIBS IS 03/178		 0.8 ng/mL 1:11 diluted with 0.4% AA and GuHCl; 1:2 dilution with citric acid and GuHCl S
P-HEP
WB		 150 μL
AxSYM NC
HET		 I: FBP immobilized through capture
FC: Pteroic acid conjugated to ALP		 CL PGA in HSA 0.9 ng/mL 1:11 diluted with folate lysis reagent, then 1:2 diluted with protein diluent S
P-EDTA
WB		 105 μL
Beckman Coulter
Access 2
UniCel DxI		 C
HET		 I: Secondary anti-FBP antibody coupled to paramagnetic particles
FC: Folic acid conjugated to ALP		 CL PGA in buffered matrix 0.5 ng/mL 1:21 diluted with 0.15% AA S
P-HEP
WB		 55 μL
Ortho Clinical Diagnostics
VITROS C
HET		 I: Biotinylated FBP coupled to streptavidin-coated well
FC: Folate conjugated to HRP		 CL PGA in buffer 0.2 ng/mL 1:41 diluted with red cell folate reagent S
P
WB		 53 μL
Elecsys 2010
E170
Cobas e411
Cobas e601		 C
HET		 I: Ruthenium-labeled FBP-folate biotin complex coupled to streptavidin-coated microparticles
FC: Biotin-labeled folate		 CL   0.6 ng/mL 1:31 diluted with 0.2% AA S
WB		 25 μL
Siemens Healthcare Diagnostics
Dimension
Vista		 C
HOM		 I: Biotinylated FBP streptavidin complex containing photosensitive dye; not immobilized
FC: Folic acid derivative containing chemiluminescent dye		 CL PGA 0.5 ng/mL   S
P-HEP		 10 μL
ACS:180 C
HET		 I: Biotinylated FBP avidin complex coupled to paramagnetic particles
FC: Acridium ester-labeled folate		 CL 5MTHF in buffer with HSA 0.25 ng/mL 1:21 diluted with 1% AA S
WB		 130 μL
ADVIA Centaur C
HET		 I: Biotinylated FBP avidin complex coupled to paramagnetic particles
FC: Acridium ester-labeled folate		 CL 5MTHF in buffer with HSA 0.35 ng/mL 1:21 diluted with 1% AA S
WB		 150 μL
Immulite 1000 C
HET		 I: Secondary anti-FBP antibody coupled to microbead
FC: Ligand-labeled folate		 CL Traceable to an IS 0.8 ng/mL 1:21 diluted with 1% AA
Requires a boil step		 S
P-HEP
WB		 200 μL
Immulite 2000 or 2500 C
P-HEP		 I: Microbead with anti-FBP antibody
FC: Ligand-labeled folate and ALP labeled antiligand		 CL Traceable to an IS 0.8 ng/mL 1:26 diluted with 0.5% AA S
P-HEP
WB		 50 μL

Adapted from Table 21.2 in Folate in Health and Disease, edited by Lynn Bailey. Boca Raton, Fla. CRC Press, 2010.

AA, ascorbic acid; ALP, alkaline phosphatase; C, competitive; CL, chemiluminescence; FL, fluorescence; FL-TR, time-resolved fluorescence; FBP, folate-binding protein; GuHCl, guanidine HCl; HET, heterogeneous; HRP, horseradish peroxidase; HSA, human serum albumin; IS, international standard; LOD, limit of detection; 5MTHF, 5-methyltetrahydrofolate; NC, noncompetitive; P, plasma; P-EDTA, EDTA plasma; PGA, pterolyglutamic acid; P-HEP, heparin plasma; S, serum, WB, whole blood