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Background
The Casoni Test is an intradermal diagnostic test, described in 1912 by Italian physician Tommaso Casoni for the identification of hydatid disease (echinococcosis), a parasitic infection caused by tapeworm species Echinococcus granulosus and/or E. multilocularis. This disease causes the formation of cysts in humans usually located in visceral organs, especially liver and lungs secondary to egg ingestion by Echinococcus from an infected animal such as dogs.
The Casoni test is performed by injecting a small sample of sterilized hydatid fluid, coming from hytadids cysts, into the skin and detecting an allergic reaction as proof if sensitization to Echinococcus antigen. This test is performed on Type I hypersensitivity reactions elicited by one of the body’s responses to a foreign substance, leading to redness and swelling (and possibly delayed symptoms) at the site where an antigen was introduced.
As was criticized for its poor accuracy (low predictive value) of the Casoni test in 20th century indeed it has high rate of false positive and negative tests. Consequently, it has been largely replaced by serology (ELISA, immunoblotting) and more modern imaging techniques — like ultrasound or CT-scans which are far more sensitive and specific.
Indications/Applications
The Casoni test was used to detect hydatid disease, especially in patients with various histories of exposure.
During the trial at a particular place, patients with cysts in their organs originated from neighbouring countries like Iraq and Syria were all given Casoni tests.
The Casoni test can be used to confirm whether or not a patient has hydatid disease in various stages of illness.
A patient with symptoms such as abdominal pain, jaundice and cough, or Casoni-positive, is likely to have acute or subacute hydatid disease. The disease need not be severe per se but is nonetheless defined as “acute” once it has demonstrated itself in some form.
The Casoni test was used to differentiate hydatid cysts from other cystic conditions, such as tumors and abscesses, in patients who had been exposed to Echinococcus.
Due to its disadvantages, the Test is now rarely used and has been replaced by more sophisticated methods to diagnose Echinococcosis.
Reference Range
Casoni test: There is no definite quantitative reference range for Casoni test. Rather, it is a visual qualitative test in which an immediate or delayed skin reaction (reddish bumpy area) at the point where antigen was injected into your arm will be seen.
Positive Reaction:
A positive reaction is indicated by the appearance of a red, raised wheal (swelling) at the injection site within 20 to 30 minutes and suggests that someone may be sensitized to Echinococcus antigens.
And in 24–48 h, erythema and swelling may emerge which represents a delayed hypersensitivity.
Negative Reaction:
Imagine a negative result The vaccine was clear and the skin at the injection site did not respond_FATAL
Because of the low specificity and sensitivity, a positive result should therefore be seen in the context with other diagnostic results.
Interpretation
Interpretation of the Casoni test results is based on a reaction to the injection of hydatid fluid antigen into skin:
Positive Test:
Indicates a positive result:
Positive (immediate reaction): A wheal and flare appears within 20–30 minutes of the injection, which reveals the humeral antibodies against Echinococcus antigens.
Delayed reaction: erythema and induration may develop after 24–48 hours, consistent with a possible delayed immune response.
But the Casoni test is of little use as a confirmatory study, since false positives are frequent and many uninfected individuals will respond positively on this assay. Diseases such as other parasitic infections or more general reactions to allergenic can have the same affect.
Negative Test:
Negative: No significant skin response to antigen injection. But a negative result does not eliminate the risk, as this test has false negatives which could be normalized in early infection or activated ARS reactions.
The main reason is that a positive or negative result of laboratory tests has limited diagnostic value regarding the presence or absence of hydatid disease. Diagnostic tools in modern day are much more accurate.
Collection And Panels
Sample type:
Antigen: Hydatid fluid which is extracted from the hydatid cysts in filtered and sterilized condition
Administration:
Control injection: Saline or non-reactive fluid is injected on the other site of the arm as a negative control.
Intradermal injection: A 0.1 mL of hydatid fluid is injected into the skin of the forearm.
Observations: Assess for any immediate reaction in 20 to 30 minutes of the injection. Any delayed reaction will be assessed after the 24 to 48 hours of the injection.
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