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Intended Use: For in vitro diagnostic use with the IMMULITE 2000 Analyzer — for the quantitative determination of L-homocysteine in human plasma or serum. This device can assist in the diagnosis and treatment of patients suspected of having hyperhomocysteinemia or homocystinuria.
Catalog Number: L2KHO2 (200 tests)
Test Code: HCY Color: Dark Gray
Warning: Specimens from patients who are on drug therapy involving S-adenosyl-methionine may show falsely elevated levels of homocysteine.
Results on specimens obtained from patients taking methotrexate, carbamazepine, phenytoin, nitrous oxide, anti-convulsants, or
6-azauridine triacetate should be interpreted with caution as these substances interfere with homocysteine determination.
Summary and Explanation
Total homocysteine (tHcy) has emerged as an important risk factor in the assessment of cardiovascular disease.3- 7,12 Hcy, a thiol-containing amino acid, is produced by the intracellular demethylation of methionine. Hcy thereby serves as a pool that can be later scavenged for use in the remanufacture of either methionine through the action of the folate-dependent enzyme methionine synthase or cysteine using the B6 dependent transsulphuration pathway.1,2 Hcy in plasma is found primarily in a protein bound form but free, oxidized and disulfide forms are also present.
Highly elevated levels of tHcy are found in patients with homocystinuria, a rare genetic disorder of the enzymes involved in Hcy metabolism.1,2,3 Homocystinuria patients exhibit arterial thromboembolism, mental retardation and early arteriosclerosis.1 Less severe genetic
defects are also associated with moderate levels of Hcy.3,4,5
Homocysteine has been identified as a indicator of cardiovascular disease. A meta-analysis of 27 epidemiological studies has suggested that a 5 µmol/L increase in tHcy could be associated with an odds ratio for coronary artery disease (CAD) of 1.6 for men and 1.8 for women, the same increase in risk as a 0.5 mmol/L increase in cholesterol.7 In addition, patients with chronic renal disease complicated by arteriosclerotic cardiovascular disease show elevated
tHcy due to the inability of the kidney to remove Hcy from the blood.1,2,3
Principle of the Procedure
Competitive Immunoassay.
The IMMULITE 2000 performs an on-line one-cycle sample pretreatment of patient plasma or serum with S-adenosyl-L- homocysteine (SAH) hydrolase and dithiothreitol (DTT) solution in a reaction tube containing no bead. After a 30-minute incubation, the treated sample is transferred to a second reaction tube containing a SAH-coated polystyrene bead and an alkaline phosphatase-labeled antibody specific for SAH. During a 30- minute incubation, the converted SAH from the sample pretreatment competes with immobilized SAH for binding alkaline phosphatase-labeled anti-SAH antibody. Unbound enzyme conjugate is removed by centrifugal wash. Substrate is added and the procedure continues as described for typical immunoassays in the Operator's Manual.
Incubation Cycles: 2 × 30 minutes. 2 test
positions per assay: 1 sample treatment cup; 1 immunoreaction cup.
Cycle 1: Release of bound homocysteine and conversion to SAH.
Cycle 2: Immunoreaction.
Specimen Collection
Heparinized and EDTA plasma are the samples of choice, but serum is also suitable for use. It is important to separate the plasma or serum from the cells as soon as possible after collection, as
