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MORROW BROWN® Allergy Diagnostics
Division Of Alkaline Corp.
P.O. Box 306
Oakhurst, NJ 07755-0306 USA
HOW TO GRADE SKIN TESTS
using THE MORROW BROWN® ALLERGY DIAGNOSTIC NEEDLE
We have inquiries from some users asking us to recommend a method of reading and grading skin test results when using the Morrow Brown® Skin Testing Needle. We are recommending the grading system developed by Standardization Committee of the Northern Society of Allergy (Scandinavia) which was first described by Aas and Belin in Acta Allergologica (Copenhagen) 27:439 (1972):
RATIONALE: Direct comparison of wheal diameters between different patients cannot be made because of differences in skin test reactivity. This is why arbitrary grading methods are a source of confusion. Therefore, a whealing reaction to a test extract must be compared to a positive standard of 5mg/ml glycerinated histamine phosphate (equivalent to 1.8mg histamine base), and a negative Standard (glycerinated diluent) in each patient.
METHOD: A wheal reaction the same size as the prick histamine control is graded +++ (3 plus) and a reaction the same size as the negative (diluent) control is indicated by - or 0. The gradings + and ++ are used for reactions between - and +++. In general, + is 1/3 the size of the histamine control and ++ is 2/3 the size. For reactions larger than +++ another plus is added for each doubling of the average diameter of the wheal. This system is precise enough for most research purposes. In the clinic the reading can be further simplified by calling any reaction larger than the positive control ++++ (4 plus), and/or measuring the diameter of unusually large reactions and noting this on the test report. Skin reactions using the Morrow Brown® Needle are often slightly smaller than those obtained with more traumatic, less consistent techniques. This means greater patient comfort and easier reading of test results when the correct grading method is used.
ALLERGEN TESTING: Actual allergy tests with antigen should be carried out with 1:10 or 1:20 W/V glycerinated extracts. DO NOT use the intradermal dilutions for prick testing.
SUMMARY: The grading method described above is simple and effective. It controls for differences in reactivity between patients and in the same patient at different times of testing. A simple millimeter rule is all that is needed to measure reactions. For the most rapid, precise reading, we recommend the Morrow Brown® Circular Millimeter Caliper which we supply to our customers upon request. Please call if you have questions regarding the use of histamine as positive control.
Contact us if you have any questions.
1-732-531-7830
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732-531-7830
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