Axis-Shield LS2 Reagent Enzymatic Homocysteine Assay
FHRWR100/200/1000, FHRWAU100/200/1000

Axis-Shield Homocysteine Control Kit
FHCY200

Homocysteine (Hcy) is a thiol-containing amino acid produced by the intracellular demethylation of methionine. Hcy is exported into plasma where it circulates mostly in its oxidized form bound to plasma proteins as a protein-Hcy mixed disulphide with albumin. Smaller amounts of reduced homocysteine and the disulphide homocystine (Hcy-SS-Hcy) are present. Total homocysteine represents the sum of all Hcy species found in plasma and serum (free plus protein bound).

Hcy is either metabolized to cysteine or to methionine. In the vitamin B6 dependent trans-sulphuration pathway Hcy is irreversibly catabolized to cysteine. A major part of Hcy is remethylated to methionine, mainly by the folate and cobalamin-dependent enzyme methionine synthase. Hcy accumulates and is excreted into the blood when these reactions are impaired.

Severely elevated concentrations of Hcy are found in subjects with homocystinuria, a rare genetic disorder of the enzymes involved in the metabolism of Hcy. Patients with homocystinuria exhibit mental retardation, early arteriosclerosis and arterial and venous thromboembolism. Hcy-reducing therapy improves the prognosis for this disease. Other less severe genetic defects that lead to moderately elevated levels of Hcy are also found.

Epidemiological studies have investigated the relationship between elevated Hcy concentrations and cardiovascular disease (CVD). A meta-analysis of 27 of these studies, including more than 4,000 patients, estimated that a 5 mmol/L increase in Hcy was associated with an odds ratio of 1.7 for cardiovascular disease or the same as that associated with 0.5 mmol/L (20 mg/dL) increase in cholesterol. Peripheral arterial disease also showed a strong association.

Certain patient groups with anemia and/or asthenia also demonstrate increased levels of plasma- or serum Hcy.

Patients with chronic renal disease experience an excess morbidity and mortality due to arteriosclerotic CVD. Elevated concentration of Hcy is a frequently observed finding in the blood of these patients. Although such patients may lack some of the vitamins involved in the metabolism of Hcy, the increased levels of Hcy are mainly due to impaired removal of Hcy from the blood by the kidney.

The following drugs; methotrexate, carbamazepine, phenytoin, nitrous oxide and 6-azauridine triacetate, may give elevated levels of homocysteine. The mechanism of action affects different parts of the metabolic pathway of homocysteine.

The Liquid Stable (LS) 2-Part  Enzymatic Homocysteine assay is intended for in vitro quantitative determination of total homocysteine in human serum and plasma.

In the Axis-Shield Enzymatic Homocysteine assay, bound or dimerised homocysteine (oxidised form) is reduced to free homocysteine, which then reacts with serine catalysed by cystathionine beta-synthase (CBS) to form L-cystathionine. Cystathionine in turn is broken down by cystathionine beta-lyase (CBL) to form homocysteine, pyruvate and ammonia. Pyruvate is then converted by lactate dehydrogenase (LDH) to lactate with NADH as coenzyme. The rate of NADH conversion to NAD is directly proportional to the concentration of homocysteine.

Features:
Instrument: Multiple platforms available (Roche, BCI, Siemens and others)
Method: Enzymatic assay
Sample type: Serum and EDTA or heparinized plasma
Sample volume 24µL
Lower limit of detection: 0.8 µmol/L
Assay Range: 1-46 µmol/L
Calibrators: 0 & 27 µmol/L
Curve Stability: 4 weeks
Time to first result: 12 minutes (calibrated Instrument)
Throughput: 36 test per hour (calibrated Instrument)
Reagents: Ready to use

Precision (1)

1) Human EDTA plasma samples were run in duplicate on 40 runs spread over 20 days according to NCCLS EP-5-A2.

The new Liquid Stable 2 reagent enzymatic homocysteine assay has  been made available as a convenience to users, with applications for use on popular clinical chemistry platforms.  Performance data are available under 'related papers' below.

*Products may not be approved for sale in all countries. Please contact your local distributor for further details.