Siemens Immulite Homocysteine 2000 User Manual page 5

The assay is traceable to an internal
standard manufactured using qualified
materials and measurement procedures.
Analytical Sensitivity: 0.5 µmol/L
Precision: Samples were repeatedly
assayed in quadruplicate over the course
of several days, for a total of 20 runs and
80 replicates. (See "Precision" table.)
Linearity: Samples were assayed under
various dilutions. (See "Linearity" table for
representative data.)
Recovery: Samples spiked 1 to 19 with
three homocysteine solutions (125, 250,
500 µmol/L), were assayed. (See
"Recovery" table for representative data.)
Specificity: The antibody is highly specific
for homocysteine. (See "Specificity" table.)
Bilirubin: Presence of conjugated and
unconjugated bilirubin in concentrations
up to 200 mg/L has no effect on results,
within the precision of the assay.
Hemolysis: Presence of hemoglobin in
concentrations up to 512 mg/dL has no
effect on results, within the precision of the
assay.
Lipemia: Presence of triglycerides in
concentrations up to 3,000 mg/dL has no
effect on results, within the precision of the
assay.
Alternate Sample Type: To determine
whether serum can be used in the
IMMULITE 2000 Homocysteine
procedure, blood was collected on ice
from 34 laboratory volunteers into
heparinized, EDTA and plain vacutainer
tubes. Samples were separated from the
cells, and matched samples were spiked
with homocysteine and then assayed by
the IMMULITE 2000 Homocysteine
procedure, with the following results.
(EDTA) = 0.98 (Heparin) + 0.85 µmol/L
r = 0.954
(Serum) = 1.02 (Heparin) – 0.53 µmol/L
r = 0.975
Means:
20.2 µmol/L (Heparin)
20.7 µmol/L (EDTA)
20.1 µmol/L (Serum)
To assess the effect of storage
temperature, heparinized, EDTA and plain
vacutainer tubes were collected from five
volunteers for each tube type. Some tubes
were stored at room temperature, while
other tubes were kept on ice for various
IMMULITE 2000 Homocysteine (PIL2KHO-14, 2007-11-20)
time periods prior to separation. The
graphs below show the effect of storage
time and temperature for heparin, EDTA
and serum. (See graphs 1-3).
Method Comparison 1: The assay was
compared to a commercially available
manual enzyme immunoassay (Kit A) on
168 plasma samples (Concentration
range: approximately 4 to 43 µmol/L. See
"Method Comparison 1" graph.) By linear
regression:
(IML 2000) = 1.0 (Kit A) + 0.24 µmol/L
r = 0.966
Means:
12.9 µmol/L (IMMULITE 2000)
12.7 µmol/L (Kit A)
Method Comparison 2: The assay was
also compared to an in-house HPLC
method in use at a reference laboratory in
the United States on 95 heparinized
plasma samples (Concentration range:
approximately 4 to 44 µmol/L. See
"Method Comparison 2" graph.) By linear
regression:
(IML 2000) = 0.97 (HPLC) + 0.71 µmol/L
r = 0.974
Means:
13.4 µmol/L (IMMULITE 2000)
13.2 µmol/L (HPLC)
Method Comparison 3: The assay was
compared to another commercially
available immunoassay (Kit B) on 113
plasma samples (Concentration range:
approximately 4 to 23 µmol/L. See
"Method Comparison 3" graph.) By linear
regression:
(IML 2000) = 0.90 (Kit B) – 0.02 µmol/L
r = 0.925
Means:
8.7 µmol/L (IMMULITE 2000)
9.6 µmol/L (Kit B)
References
1) Selhub J, Miller JW. The pathogenesis of
homocysteinemia: interruption of the coordinate
regulation by s-adenosylmethionine of the
remethylation and transsulfuration of
homocysteine. Am J Clin Nutr 1992;55:131-8. 2)
Jacques PF, Bostom AG, Williams RR, et al.
Relation between folate status, a common
mutation in methylenetetrahydrofolate reductase
and plasma homocysteine concentrations.
Circulation 1996;93:7-9. 3) Malinow MR. Plasma
homocysteine and arterial occlusive diseases: A
mini review. Clin Chem. 1995;40:173-76. 4)
Clarke R, Daly L, Robinson K, Naughten E, et al.
Hyperhomocysteinemia: An independent risk
5