Available Assays

Acceptable assays for plasma homocyst(e)ine include HPLC and immunoassay.28 Each laboratory should determine its own gender- and local population-specific reference ranges. The basal plasma homocysteine level should be determined first, and if elevated, further investigation regarding the potential cause as well as therapeutic intervention should be considered. It is unclear whether plasma homocysteine levels should be tested after an overnight fast. Because plasma homocysteine levels can be elevated for several months after myocardial infarction or stroke, testing should be delayed accordingly. In addition to vitamin deficiency, impaired renal function and hypothyroidism are other common causes of hyperhomo-cyst(e)inemia. Vitamin B12 deficiency should be excluded prior to beginning therapy since high-dose folic-acid therapy can precipitate acute B12 neuropathy. If the basal homocysteine level is normal,methionine loading (0.1 g/kg body weight or 3.8gm/m2 body surface area with measurement of plasma homocysteine 4 to 6 hours after the load) should be considered since 25% to 40% of symptomatic patients develop hyperhomocyst(e)inemia only after methionine loading. Therapy includes folic acid (0.5 to 1.0mg/day), vitamin B12 (400 to 1000 pg/day), and/or vitamin B6 (20 to 50mg/day).30

Acknowledgments

Funded, in part, by grants from the National Institutes of Health (HL66216), the Centers for Disease Control and Prevention (TS306), U.S. Public Health Service; the Doris Duke Charitable Foundation Innovation in Clinical Research; and Mayo Foundation.

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Section II

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