1. General
Parenteral Drug Products should be inspected visually for particulate matter
and discoloration prior to administration, whenever solution and container
permit.
2. Scratch, Prick or Puncture Testing Methods
There are two general methods of skin testing. (1) The skin is scarified first,
and the extract is then applied. (2) A drop of extract is put onto the skin,
and a prick or puncture is made through the drop. Avoid touching tip of dropper
to skin. Either method is satisfactory, but the second requires that the
instrument be cleansed between tests or that separate needles be used.
The extracts for scratch, prick or puncture testing are supplied
in dropper vials and should be kept in a rack or box in rows of 10 vials
corresponding to the rows of tests to be applied to the skin.
All skin tests should be validated by appropriate positive
control tests (e.g., histamine) and negative control tests (e.g., Glycerin,
Albumin Saline with Phenol (0.4%), or Buffered Saline with Phenol). The
negative control test should be the same material as is used as a diluting
fluid in the tested extracts. Diluting fluid is used in the same way as an
active test extract.
Test sites should be examined at 15 and 30 minutes. To prevent
excessive absorption, wipe off antigens producing large reactions as soon as
the wheal appears. Record the size of the reaction. Delayed reactions may
rarely occur from tests, so it may be helpful to examine the test sites in 24
hours.
Use of Scarifiers and Spacing. Make
scarifications at least 2.5 cm apart. Use more space between pollen tests to
prevent smearing into adjacent sites. Hold the scarifier between the thumb and
index finger, press the sharp edge of the instrument against the skin and twirl
instrument rapidly. The scratch should disrupt only the outer layers of
epidermis but should not produce immediate oozing of blood. The amount of
pressure needed to produce a satisfactory scratch will vary between patients
according to the thickness or fragility of their skin. Experience will indicate
the proper amount of pressure to exert in making the scratch. If the scarifier
is kept sharp and the scratch made quickly, discomfort to the patient is
minimized.
Use of Prick Test Needles. The skin is
cleaned and single drops of each extract applied to the properly identified
test sites. A small, sterile disposable needle, such as a 1/2-inch 26 gauge
needle (with the bevel up), a bifurcated vaccinating needle, or a Prick
Lancetter™ is inserted through the drop superficially into the skin, the skin lifted
slightly and the needle withdrawn. No bleeding should be produced. After about 1
minute the extract may be wiped away.
3. Most Satisfactory Sites for Testing
Prior to testing, clean the skin area to be tested with ether or alcohol and
allow to dry. Use a sterile instrument for each patient. The back or the volar
surface of the arms are the most satisfactory sites for testing. Skin of the
posterior thighs or abdomen may be used if necessary. Avoid very hairy areas
where possible, since the reactions will be smaller and more difficult to
interpret. The most satisfactory areas of the back are from the posterior
axillary fold to 2.5 cm from the spinal column, and from the top of the scapula
to the lower rib margins. The best areas of the arms are the volar surfaces
from the axilla to 2.5 or 5 cm above the wrist, skipping the anti-cubital
space.
4. Use of Antigen Mixes
The use of complicated mixes of unrelated pollens for testing is not
recommended since in the case of a positive reaction, it does not indicate
which pollen(s) are responsible, and, in the case of a negative reaction, it
fails to indicate whether the individual pollens at full concentration would
give a positive reaction.
5. Reading Skin Test Reactions
A positive reaction consists of an urticarial wheal with surrounding erythema
(resembling somewhat a mosquito bite reaction) larger than the control site.
The smallest reaction considered positive is erythema with a central papule at
least 5 mm in diameter. In some instances with no reaction at the control site,
erythema may be considered an indication of sensitivity. In general, the size
of wheal and erythema response correlates directly with the patient’s
sensitivity to that allergen.
Standardized Products
(a) Mites:
The skin test concentration of 30,000 AU/mL in dropper vials is used for
scratch, prick or puncture testing. Puncture tests performed on 12 highly
sensitive subjects showed the following:
Species
| Mean Sum of Wheal ± Std. Dev. (mm)
| Mean Sum of Erythema ± Std. Dev. (mm)
|
|---|
D. farinae
| 22.4 ± 10.7
| 82.2 ± 21.7
|
D. pteronyssinus
| 24.0 ± 9.9
| 89.3 ± 24.5 |
The sum of a skin response is the sum of the longest diameter and
the mid-point orthogonal diameter.
(b) Cat Hair and Cat Pelt: The skin test concentration of 10,000
BAU/mL (10-19.9 Fel d 1 Units/mL) in dropper vials is used for prick or
puncture testing. Puncture tests performed on 15 highly sensitive subjects
showed the following:
Product
| Mean Sum of Wheal ± Std. Dev (mm)
| Mean Sum of Erythema ± Std. Dev (mm)
|
|---|
Standardized Cat Hair
| 15.1 ± 3.8
| 73.3 ± 14.3
|
Standardized Cat Pelt
| 13.9 ± 4.3
| 67.3 ± 13.3 |
The sum of a skin response is the sum of the longest diameter
and the mid-point orthogonal diameter.
(c) Ragweed pollen (Short Ragweed or Giant and Short Ragweed
Mixture) Antigen E Assayed: Short Ragweed extract at 1:20 w/v in 50% glycerin
containing approximately 100 to 300 units of Amb a 1/mL or Giant and Short
Ragweed Mix at 1:20 w/v in 50% glycerin containing approximately 50 to 150
units of Amb a 1/mL are usually used for scratch, prick or puncture testing.
Refer to the following table to determine the skin test sensitivity
grade. The corresponding ∑E (sum of the longest diameter and the mid-point
orthogonal diameters of erythema) is also presented.
Grade
| Erythema mm
| Papule or Wheal mm
| Corresponding mm ∑E
|
0
| <5
| <5
| <10
|
| ± | 5-10
| 5-10
| 10-20
|
1+
| 11-20
| 5-10
| 20-40
|
2+
| 21-30
| 5-10
| 40-60
|
3+
| 31-40
| 10-15 (a)
| 60-80
|
4+
| >40
| >15 (b)
| >80
|
(a) or with pseudopods (b) or with many pseudopods
A positive skin reaction to any allergen must be interpreted in
light of the patient’s history of symptoms, time of the year, and known exposures.
THE SKIN TESTS ARE IN NO WAY A SUBSTITUTE FOR A CAREFUL ALLERGIC HISTORY. THEY
SERVE AS ADDITIONAL INFORMATION TO AID IN IDENTIFYING CAUSATIVE ALLERGENS IN
PATIENTS WITH ALLERGIC DISORDERS.