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Coagulation

Coagulation laboratory tests

Homocysteine assay


Reviewer: Jeremy Parsons, M.D. (see Reviewers page)
Revised: 10 February 2013, last major update November 2012
Copyright: (c) 2002-2013, PathologyOutlines.com, Inc.

General
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● Suspected risk factor for arerial or venous thrombosis, although evidence is weak (Arch Pathol Lab Med 2002;126:1367)
● 70% of homocysteine is bound to albumin, 30% is oxidized to disulfides, 2% is free
● Reference range is 5-15 micromolar (reflects free, non-bound form)
● Gender and local population specific reference ranges are strongly recommended, because levels are affected by dietary intake of methionine and vitamins, gender and age (lower in premenopausal women)
● High levels may also be due to vitamin B12 deficiency, post-myocardial infarction or stroke
● Usually recommended to measure after 10 hour fast, although this may not be necessary
● Increase test specificity by measuring 3-6 hours after methionine load of 0.1 g of L-methionine/kg
● Must put specimen on ice if plasma separation cannot be performed within 30 minutes, because homocysteine is produced and exported by red blood cells and levels rise after collection in EDTA-anticoagulated tubes
● Alternatively can use acid citrate tubes and hold for up to 6 hours

Methodology
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Reduce all forms of homocysteine to free homocysteine, then quantify using either:
● High performance liquid chromatography is standard (Am J Clin Pathol 2008;130:969)
● Fluorescence based immunoassay (Abbott’s IMx analyzer) - reduce using dithiothreitol, then convert to S-adenosyl-L-homocysteine (SAH) via SAH hydrolase; SAH is measured with monoclonal antibody and fluorescent tracer
● Conventional amino acid analyzer with separation column (slow, but can also detect related amino acids, such as methionine, cystathionine and cysteine)

End of Coagulation > Coagulation laboratory tests > Homocysteine assay


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