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A substrate for the enzyme is applied, and catalysis by the enzyme leads to a change in color or fluorescence. ELISA results are reported as a number; the most controversial aspect of this test is determining the "cut-off" point between a positive and a negative result. A cut-off point may be determined by comparing it with a known standard.
A value of greater than 1.5 units relative to a control serum is considered a positive ELISA test for the anti-histone antibodies. Patients with drug-induced lupus erythematosus typically have positive tests for anti-histone antibodies but do not have indications for anti-dsDNA antibodies. Patients with idiopathic systemic lupus erythematosus ...
Sometimes, retesting the donor in several months will produce a negative ELISA antibody test. This is why a confirmatory western blot is always used before reporting a "positive" HIV test result. [citation needed] Rare false positive results due to factors unrelated to HIV exposure are found more often with the ELISA test than with the western ...
It is conventionally expressed as the inverse of the greatest dilution level that still gives a positive result on some test. ELISA is a common means of determining antibody titers. For example, the indirect Coombs test detects the presence of anti-Rh antibodies in a pregnant woman's blood serum. A patient might be reported to have an "indirect ...
Most people who take a drug test take a presumptive test, cheaper and faster than other methods of testing. However, it is less accurate and can render false results. The FDA recommends for confirmatory testing to be conducted and the placing of a warning label on the presumptive drug test: "This assay provides only a preliminary result.
In performing a test, laboratory clinicians will mix a patient's cerebrospinal fluid, serum or urine with the coated latex particles in serial dilutions with normal saline (important to avoid the prozone effect) and observe for agglutination (clumping). Agglutination of the beads in any of the dilutions is considered a positive result ...
In an agglutination test, a person's serum (which contains antibodies) is added to a test tube, which contains a particular antigen. If the antibodies interact with the antigen to form immune complexes , called agglutination, then the test is interpreted as positive.
When skin not exposed to the sun is tested, a positive direct IF (the so-called Lupus band test) is an evidence of systemic lupus erythematosus. [2] Direct fluorescent antibody can also be used to detect parasitic infections, as was pioneered by Sadun, et al. (1960).