Dosage:
Soluprick SQ Grass Pollen 10 HEP is recommended as the optimal biological potency of the allergen when taking into account the meaning of high sensitivity related to high specificity. The potency is expressed in HEP (Histamine Equivalent in Prick testing) which is related to the allergenic activity of the allergen product in the skin of the allergic patient.
ALK Positive control (histamine dihydrochloride 10 mg/ml) is used as reference and ALK Negative control (Saline solution) is used to evaluate unspecific reactions.
When performing a SPT the amount of solution introduced into the superficial layer of the skin is extremely low, approximately 3 x 10
-3 µ l. (S. Dreborg, Allergy no. 10, Vol 44, 1989)
Paediatric population
Prick testing in children is already possible after the first year of life depending on the child's constitution, but in general should not be performed before the age of 4.
Skin prick test technique
- The SPT is preferably performed on the volar side of the forearm. Alternatively the test can be performed on the back of the patient.
- The skin must be dry and clean and may be disinfected with 70% alcohol.
- Each test preparation and the controls are applied in droplets on the skin in an appropriate distance from each other (a numbered tape can be used).
- The superficial layer of the skin is pierced with an ALK Lancet perpendicular to the skin through the droplet. Hold it for 1 second and draw back the lancet. For each test preparation and control a new sterile, disposable ALK Lancet is used.
The positive control is applied last.
- The droplets are wiped off with a tissue. Do not mix the preparations by sweeping!
- Start to read the reaction of the preparations after 15 minutes beginning with the positive control. A positive reaction is a pale wheal (oedema) with a red flare (erythema). To record the wheal in the patient's report: mark the contour of the wheal with a pen, stick transparent tape over the wheal. Press and transfer the tape to the report. The flare can be recorded likewise.
Size of the wheal
The mean wheal diameter of the allergen product (D
a) and of the histamine control (D
h) is calculated as D = (D
l + d
p )/2, where D
l is the longest diameter and d
p is the diameter mid-ortogonal to D
l.
Interpretation of results
- Reactions of the allergen product can be graded in relation to the histamine control reaction. This relation is called the skin index (SI).
SI = Da/Dh 0 | : negative reaction |
+ | : SI < 0.5 |
++ | : 0.5 < SI < 1.0 |
+++ | : 1.0 < SI < 2.0 |
++++ | : 2.0 < SI |
- By use of a biological standardised allergen product a mean wheal diameter ≥ 3 mm indicates that the patient is sensitized to the respective allergen source.