Homocysteine is an amino acid. It is elevated in vitamins B6, B9 (folate) and B12 deficiencies. Elevated homocysteine level is now considered an independent risk factor for heart disease, stroke and recurrent miscarriage.
A homocysteine test is often done alongside an MMA test. Several genetic factors can result in irregular homocysteine levels, both high and low.
Read more about the homocysteine blood test