Comparison of three different plasma homocysteine assays with gas chromatography-mass spectrometry.
BACKGROUND
Various methods are available to measure plasma total homocyst(e)ine (tHcy) concentrations, but whether plasma tHcy assays may be used interchangeably is not known.


METHODS
Results from three different methods [HPLC with fluorescence detection, enzyme immunoassay (EIA), and fluorescence polarization immunoassay (FPIA)] to determine fasting (n = 163) and post-methionine load (n = 80) plasma tHcy concentrations were compared with those obtained by gas chromatography-mass spectrometry (GC-MS). Difference plots on non-transformed and log-transformed data were used to assess the agreement between HPLC and GC-MS, EIA and GC-MS, and FPIA and GC-MS.


RESULTS
The closest agreement between methods was observed between GC-MS and FPIA for fasting tHcy concentrations, with 95% of the FPIA values between 19% above and 24% below the corresponding GC-MS results. Post-methionine load tHcy concentrations measured by EIA showed the least agreement with GC-MS, with 95% of values measured by EIA ranging between 52% above and 16% below the GC-MS values. With respect to GC-MS, the above-mentioned methods showed a negative bias for fasting tHcy concentrations, but a positive bias for both immunoassays for post-methionine load tHcy concentrations.


CONCLUSIONS
The agreement among methods is insufficient to allow them to be used interchangeably. The intermethod differences emphasize the need for standardization of plasma tHcy assays.
Ubbink
J B
JB
Department of Chemical Pathology, University of Pretoria, P.O. Box 2034, Pretoria 0001, South Africa. jubbink@medic.up.ac.za
Delport
R
R
Riezler
R
R
Vermaak
W J
WJ
D016231:Fluorescence Polarization Immunoassay; D005456:Fluorescent Dyes; D005464:Fluorobenzenes; D008401:Gas Chromatography-Mass Spectrometry; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D007124:Immunoenzyme Techniques; D011933:Reagent Kits, Diagnostic
D005456:Fluorescent Dyes; D005464:Fluorobenzenes; D011933:Reagent Kits, Diagnostic; D006710:Homocysteine; C037802:7-fluorobenzo-2-oxa-1,3-diazole-4-sulfonate