Homocysteine

Description
Homocysteine is an amino acid measured in plasma that is related to a higher risk of coronary heart disease, stroke and peripheral vascular disease (http://www.americanheart.org/presenter.jhtml?identifier=535). Homocysteine may have an effect on atherosclerosis by damaging the inner lining of arteries and promoting blood clots.

Approximately one third of those older than 65 years have elevated homocysteine levels (>14 mol/L) (Selhub et al., 1993). Although the prevalence may have declined since dietary fortification with folate began in 1996 (Jacques et al, 1999; Crimmins et al., forthcoming). Homocysteine levels are related to vitamin intake particularly B6 and B12 (Mudd et al., 1985; Jacques et al., 1999). Because of this evidence, several randomized trials are under way to test whether vitamin supplementation decreases cardiovascular events (Hankey and Eikelboom, 1999).

Significance of Measurement
Homocysteine has garnered recent attention because of its importance in predicting many of the major health outcomes common in aging populations such as cardiovascular disease, peripheral vascular disease, and poorer cognitive function (Arnesen et al., 1995; Jacques and Riggs, 1995; Riggs et al., 1996; Verhoef et al., 1996).

Experimental evidence suggests that elevated plasma homocysteine levels may cause toxicity by a variety of mechanisms, including oxidative damage, which has been linked to an increased rate of aging (Loscalzo, 1996; Hensley and. Floyd, 2002).

Methods of Measurement
The method used by the laboratory at Quest Diagnostics requires 1 mL (0.2 mL minimum) room temperature serum, heparin plasma, or EDTA plasma. A >8-hour fast prior to sample collection is recommended.

Homocysteine levels increase ~10% for every hour the serum/plasma is not separated from the red blood cells using a centrifuge at room temperature. Once separated, serum/plasma is stable for: 4-7 days at room temperature; 2 weeks at 2-8C; and several years at -20C (http://www.questdiagnostics.com/hcp/intguide/jsp/showintguidepage.jsp?fn=TS_Homocysteine.htm)

References
· American Heart Association. (2005). What is homocysteine? Retrieved March 28, 2005, from http://www.americanheart.org/presenter.jhtml?identifier=535
· Arnesen, E., Refsum, H., Bonaa, K.H., Ueland, P.M., Forde, O.H., & Bnordrehaug, J.E. (1995). Serum total homocysteine and coronary heart disease. International Journal of Epidemiology, 24(4), 704-409.
· Crimmins, E., Alley, D., Reynolds, S., Johnston, M., Karlamangla, A., & Seeman, T. Changes in biological markers of health: Older Americans in the 1990s. Journal of Gerontology: Medical Sciences, forthcoming.
· Hankey, G.J., & Eikelboom, J.W. (1999). Homocysteine and vascular disease. Lancet, 354, 407–413.
· Hensley, K., & Floyd, R.A. (2002). Reactive oxygen species and protein oxidation in aging: A look back, a look ahead. Archives of Biochemistry and Biophysics, 397, 377–383.
· Jacques, P., & Riggs, K. (1995). Vitamins as risk factors for age-related diseases. In I.H. Rosenberg (Ed.), Nutritional Assessment of Elderly Population: Measure and Function. New York: Raven Press.
· Jacques, P.F., Selhub, J., Bostom, A.G., Wilson, P.W.F., & Rosenberg, I.H. (1999). The effect of folic acid fortification on plasma folate and total homocysteine concentrations. The New England Journal of Medicine, 340, 1449–1454.
· Loscalzo, J. (1996). The oxidant stress of hyperhomocysteinemia. Journal of Clinical Investigation, 98, 5–7.
· Mudd, S.H., Mudd, F., Skovby, H.L., Pettigrew, K.D., Wilcken, B., Pyeritz, R.E., et al. (1985). The natural history of homocystinuria due to cystathionine beta-synthase deficiency. American Journal of Human Genetics, 37, 1–31.
· Questdiagnostics. (2002). Homocysteine: Test summary. Retrieved March 28, 2005, from http://www.questdiagnostics.com/hcp/intguide/jsp/showintguidepage.jsp?fn=TS_Homocysteine.htm
· Riggs, K.M., Spiro, A., Tucker, K., & Rush, D. (1996). Relations of vitamin B-12, vitamin B-6, folate and homocysteine to cognitive performance in the Normative Aging Study. American Journal of Clinical Nutrition, 63, 306-314.
· Selhub, J., Jacques, P.F., Wilson, P.W., Rush, D., & Rosenberg, I.H. (1993). Vitamin status and intake as primary determinants of homocysteinemia in an elderly population. Journal of the American Medical Association, 270, 2693–2698.
· Verhoef, P., Stampfer, M., Buring, J., Gaziano, J., Allen, R., Stabler, S., et al. (1996). Homocysteine metabolism and risk of myocardial infarction: Relation with vitamins B6, B12, and folate. American Journal of Epidemiology, 143, 845-859.