ImmunoCard H. pylori
A rapid Enzyme Immunoassay for the Detection of IgG
to Helicobacter pylori in Human Serum, Plasma and Whole Blood.
INTRODUCTION:
The laboratory will be performing
in-house testing for qualitative IgG to Helicobacter pylori using the Immunocard
H. pylori assay.
INTENDED USE:
The ImunoCard H. pylori enzyme immunoassay (EIA) is an
in vitro qualitative procedure for the detection of IgG to Helicobacter
pylori in human serum, plasma or whole blood. Test results are
intended to aid in the diagnosis of H. pylori infection.
EXPLANATION:
The importance of Helicobacter pylori in gastrointestinal diseases
has increased greatly since Marshall and Warren described the presence of
campylobacter-like organisms in the antral mucosa of patients with histological
evidence of antrum gastritis and peptic ulcers especially duodenal ulcers.
Though a causative relationship has not yet been fully established, the strong
correlation between the presence of H. pylori and histologically
confirmed gastritis, PUD and gastric carcinoma can no longer be debated.
The ecological niche in humans appears to be restricted to the stomach and
duodenum. Patients who harbor the organism are divided into two basic groups.
The first are those who are said to be "colonized". These patients
have the organism, yet have no signs of the disease. Those with symptoms are
considered to be infected. The process by which a colonized individual becomes
infected remains unclear. The process by which patients become colonized is also
still under investigation.
The diagnostic strategies for the determination of H. pylori have
developed along two lines. The first, a gastric biopsy, involves the direct
detection of the organism and is invasive. This strategy has the advantage of
being able to detect active infections while being highly specific with a very
high positive predictive value. The difficulties associated with this approach
is that there is a risk and discomfort to the patient. In addition, H. pylori tends to colonize in patches and may be missed totally in the biopsy. The
second, a noninvasive approach, involves the detection of the organism's urease
or the detection of antibodies made to H. pylori, which is the most
common noninvasive approach. Through an indirect approach, the correlation
between histological gastritis, the presence of H. pylori, and
seropositivity is extremely strong. The disadvantages of these tests are that
most require instruction to be interpreted and many have a lower specificity due
to cross reactions from other organisms. Their major advantage is that they are
rapid and offer high sensitivity.
PERFORMANCE CHARACTERISTICS:
ImmnoCard/Biopsy Urease Test
Sensitivity 98.2%
Specificity 81.1%
Agreement 86.4%
ImmunoCard/Competitor's EIA
Sensitivity 97.0%
Specificity 98.1%
Agreement 97.6%
LIMITATIONS OF THE PROCEDURE:
- ImmunoCard H. pylori test should
be used in conjunction with information from the patient clinical evaluation
and other diagnostic procedures.
- This test should only be used on
patients who present symptoms suggestive of gastrointestinal disease. The
ImmunoCard test is not intended for use with asymptomatic patients.
- A positive test result does not
distinguish between an active infection and colonization by H. pylori.
- ImmunoCard is a qualitative test that
only
- A negative test result indicates the
absence of IgG antibody to H. pylori or that the IgG level is below
that which can be detected by this test.
- ImmunoCard has not been tested in pediatric
populations. Therefore, no performance characteristics have been established
for this group.
EXPECTED VALUES:
Studies on the epidemiology of H. pylori have shown that this
organism is present worldwide. Gastritis caused by H. pylori has been
shown to correlate with age, ethnic background, family size and socioeconomic
status. It is not uncommon to see 50% positivity in those who are 60 years or
older. The frequency of positivity in duodenal ulcers is about 80%. The
positivity rates clearly depend on the sample population and how the
population is defined.
The ImmunoCard test detects the presence of IgG antibodies to
H. pylori in
serum, plasma, and whole blood. Sera from 43.2% of a general symptomatic
population were antibody positive by the ImmunoCard. There was a 99.1%
correlation of whole blood and serum results in a general population of
symptomatic and asymptomatic individuals.
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