Normally most people don't fast for homocysteine although they really should
as  foods high in Methionine. The specimen of choice is also EDTA unclotted
blood rather than serum.

http://www.nutritiondata.com/foods-000084000000000000000.html

Using any of the standard analytical methods, values between 5 and 15 mmol/L
are generally considered normal in the fasting state, albeit not optimal
(<10 mmol/L).6,7  Kang and coworkers have classified hyperhomocysteinemia as
moderate (15 to 30 mmol/L), intermediate (>30 to 100 mmol/L) and severe
(>100 mmol/L) on the basis of concentrations measured during fasting.8
Levels tend to increase with age.

8  Kang SS, Wong PW, Malinow MR. Ann Rev Nutr 1992; 12: 279-298.

http://www.itxm.org/tmu2003/issue2003-6.htm

For Methionine Load Test, the reference values for homocysteine 4 hours
after an oral methionine load of 100 mg per kilogram body weight is 5.0 to
20.0 umol/L.

http://www.dlslab.com/dls/page_server/1E87D4B4DA5AD497E16E2D675D