Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

SRW
82667
colonies when cultured on sorbitol MacConkey (SMAC) agar, but the majority of non-O157:H7 Shiga
toxin-producing Escherichia coli strains ferment sorbitol and, therefore, are undetectable by this method.
The Vero cell line is susceptible to the Shiga toxin, but the assay can take up to 48 hours and is
nonspecific. Commercial enzyme-linked immunosorbent assay (ELISA) antigen detection kits have a
sensitivity of 90% when compared to culture, but an overnight enrichment step is necessary for adequate
sensitivity. PCR detection of stx, the gene encoding Shiga toxin, directly from stool specimens is a
sensitive and specific technique, providing same-day results. PCR assay identifies non-O157:H7 Shiga
toxin-producing bacteria, extending the utility beyond strains identifiable on SMAC agar.
Useful For: Sensitive, specific, and rapid detection of the presence of Shiga toxin-producing
organisms such as Escherichia coli O157:H7 and Shigella dysenteriae type 1 in stool
Interpretation: A positive PCR result indicates the likely presence of Shiga toxin-producing
Escherichia coli in the specimen. Although Shigella dysenteriae serotype 1 may produce a positive
result, it is extremely rare in the United States. A negative result indicates the absence of detectable
Shiga toxin DNA in the specimen, but does not rule out the presence of Shiga toxin-producing
Escherichia coli, as false-negative results may occur due to inhibition of PCR, sequence variability
underlying the primers and probes, or the presence of the Shiga toxin gene in quantities less than the
limit of detection of the assay. Shiga toxins are encoded on mobile genetic elements and can
theoretically be lost by their bacterial host.
Reference Values:
Not applicable
Clinical References: 1. Gould LH, Bopp C: Recommendations for diagnosis of Shiga
toxin-producing Escherichia coli infection by clinical laboratories. MMWR Morb Mortal Wkly Rep
2009 Oct; 16:v58 2. Grys TE, Sloan LM, Rosenblatt JE, Patel R: Rapid and sensitive detection of Shiga
toxin-producing Escherichia coli from nonenriched stool specimens by real-time PCR in comparison to
enzyme immunoassay and culture. J Clin Microbiol 2009;47:2008-2012 3. Grys TE, Patel R: Update on
Shiga toxin-producing Escherichia coli. Mayo Clinic, Mayo Medical Laboratories Communique 4. Nyre
LM, Kiemele DL, Zomok CD, et al: Clinical experience with rapid PCR for detection of Shiga toxin in
stool. Abstract of the Annual Meeting of the American Society for Microbiology, 2010 General
Meeting, San Diego, CA, May 23-27, 2010
Short Ragweed, IgE
Clinical Information: Clinical manifestations of immediate hypersensitivity (allergic) diseases are
caused by the release of proinflammatory mediators (histamine, leukotrienes, and prostaglandins) from
immunoglobulin E (IgE)-sensitized effector cells (mast cells and basophils) when cell-bound IgE
antibodies interact with allergen. In vitro serum testing for IgE antibodies provides an indication of the
immune response to allergen(s) that may be associated with allergic disease. The allergens chosen for
testing often depend upon the age of the patient, history of allergen exposure, season of the year, and
clinical manifestations. In individuals predisposed to develop allergic disease(s), the sequence of
sensitization and clinical manifestations proceed as follows: eczema and respiratory disease (rhinitis and
bronchospasm) in infants and children less than 5 years due to food sensitivity (milk, egg, soy, and
wheat proteins) followed by respiratory disease (rhinitis and asthma) in older children and adults due to
sensitivity to inhalant allergens (dust mite, mold, and pollen inhalants).
Useful For: Testing for IgE antibodies may be useful to establish the diagnosis of an allergic disease
and to define the allergens responsible for eliciting signs and symptoms. Testing also may be useful to
identify allergens which may be responsible for allergic disease and/or anaphylactic episode, to confirm
sensitization to particular allergens prior to beginning immunotherapy, and to investigate the specificity
of allergic reactions to insect venom allergens, drugs, or chemical allergens.
Interpretation: Detection of IgE antibodies in serum (Class 1 or greater) indicates an increased
likelihood of allergic disease as opposed to other etiologies and defines the allergens that may be
responsible for eliciting signs and symptoms. The level of IgE antibodies in serum varies directly with
the concentration of IgE antibodies expressed as a class score or kU/L.
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