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Paediatric Laboratory Medicine

Homocysteine, Blood

Clinical Significance

Homocysteine (HCY) is a thiol-containing amino acid produced by the intracellular demethylation of methionine. Homocysteine accumulates and is excreted into the blood when these reactions are impaired. Impaired homocysteine metabolism results in hyperhomocysteinemia (increased levels of homocysteine in plasma or serum) or homocystinuria (high plasma levels cause homocysteine to be excreted in urine). Hyperhomocysteinemia is caused by nutritional and genetic deficiencies. The majority of elevated homocysteine cases (two-thirds) in the general population are due to deficiency of folic acid, vitamin B6 and vitamin B12. Severely elevated concentrations of total homocysteine are found in subjects with homocystinuria, a rare genetic disorder of the enzymes involved in the metabolism of homocysteine. Studies have investigated the relationship between elevated homocysteine concentrations and cardiovascular disease (CVD), indicating homocysteine as an important marker for risk assessment

Test Name

Homocysteine, Blood

Test Code



Biochemistry - Biochemistry



External Proficiency Testing


Specimen Type

Serum, Lithium Heparin / K-EDTA plasma

Minimum Specimen Requirements

300 uL

Approval is not required

CPT Codes


Shipping and Contact Information

The Hospital for Sick Children
Rapid Response Laboratory
170 Elizabeth Street, Room 3642
Toronto, ON
M5G 2G3
Phone: 416-813-7200
Phone: 1-855-381-3212

Reference Range

<5y : 0.5-11.0 µmol/L
6-12y : 5.0-12.0 µmol/L
13-59y : 5.0-15.0 µmol/L
>60y : 5.0-20.0 µmol/L