Siemens Immulite Homocysteine 2000 User Manual page 2

IMMULITE
English
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.
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.
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.
patients exhibit arterial thromboembolism,
mental retardation and early
1
arteriosclerosis. Less severe genetic
2
®
2000 Homocysteine
1,2,3
Homocystinuria
defects are also associated with moderate
levels of Hcy.
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.
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.
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.
3-
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.
1,2
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
IMMULITE 2000 Homocysteine (PIL2KHO-14, 2007-11-20)
3,4,5
7
In addition,
1,2,3