Assay

Immunoglobulin E (Specific)

Key Words

Specific immunoglobulin E, RAST, SIGE

Specimen Collection

Serum (brown)

Turnaround time

7 days

Test indications

IgE against specific allergens (‘specific IgE’) tests used to be called ‘RAST tests’ but a different type of assay is now used. A very wide range of allergens are available including most inhalant allergens, foodstuffs, venoms and drugs. Therefore, the choice of allergen for SIgE test MUST be based on specific substance or substances though to be the cause of acute or chronic allergy-like symptoms in the patient. The allergens to be tested must be written on the request form; general screening tests are not available, and if not quoted or indecipherable the sample will be stored for up to two weeks pending clarification.

The concentration of sIgE may not correlate with the severity of the allergy.  Sensitisation to an allergen can occur without overt clinical allergy symptoms and some patients can outgrow their allergy but remain SIGE positive. Following anaphylaxis, specific IgE testing should be delayed for approximately 6 weeks, thus skin prick testing may be required. It is essential that all SIGE results are interpreted alongside a full allergic history and any tests that have been performed, such as skin prick tests 

Specific IgE testing to drugs is very insensitive, so a positive result is helpful, but a negative result does not exclude allergy.

Please refer to Allergy interpretation section for more information and component testing. 

Methodology

Enzyme immunoassay

Interferences

Very high levels of total IgE (e.g. >1000 KUa/L) may cause false positive specific IgE results. 

Reference Range

Grade 0=<0.35 KUa/L

Grade 1= 0.35-0.70 KUa/L

Grade 2= 0.70 - 3.5 KUa/L

Grade 3= 3.5 - 17.5 KUa/L

Grade 4= 17.50 - 50.0 KUa/L

Grade 5= 50.0 - 100.0 KUa/L

Grade 6= >100.0 KUa/L

Analytical error

Reference change value

N/A